FORECAST Research and Development

Adams, J. L., D. J. Stensrud, 2005: Impact of tropical easterly waves on gulf surges during the North American Monsoon. Sixth Conference on Coastal Meteorology, San Diego, CA, USA, American Meteorological Society, 5.7.

Adams, J. L., D. J. Stensrud, 2007: Impact of tropical easterly waves on the North American monsoon. Journal of Climate, 20, 1219-1238.

The North American monsoon (NAM) is a prominent summertime feature over northwestern Mexico and the southwestern United States. It is characterized by a distinct shift in midlevel winds from westerly to easterly as well as a sharp, marked increase in rainfall. This maximum in rainfall accounts for 60%–80% of the annual precipitation in northwestern Mexico and nearly 40% of the yearly rainfall over the southwestern United States. Gulf surges, or coastally trapped disturbances that occur over the Gulf of California, are important mechanisms in supplying the necessary moisture for the monsoon and are hypothesized in previous studies to be initiated by the passage of a tropical easterly wave (TEW). Since the actual number of TEWs varies from year to year, it is possible that TEWs are responsible for producing some of the interannual variability in the moisture flux and rainfall seen in the NAM.

To explore the impact of TEWs on the NAM, four 1-month periods are chosen for study that represent a reasonable variability in TEW activity. Two continuous month-long simulations are produced for each of the selected months using the Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model. One simulation is a control run that uses the complete boundary condition data, whereas a harmonic analysis is used to remove TEWs with periods of approximately 3.5 to 7.5 days from the model boundary conditions in the second simulation. These simulations with and without TEWs in the boundary conditions are compared to determine the impact of the waves on the NAM. Fields such as meridional moisture flux, rainfall totals, and surge occurrences are examined to define similarities and differences between the model runs. Results suggest that the removal of TEWs not only reduces the strength of gulf surges, but also rearranges rainfall over the monsoon region. Results further suggest that TEWs influence rainfall over the Southern Plains of the United States, with TEWs leading to less rainfall in this region. While these results are only suggestive, since rainfall is the most difficult model forecast parameter, it may be that TEWs alone can explain part of the inverse relationship between NAM and Southern Plains rainfall.

Adhikari, P., Y. Hong, K. R. Douglas, D. B. Kirschbaum, J. J. Gourley, R. F. Adler, G. R. Brakenridge, 2010: A digitized global flood inventory (1998-2008): Compilation and preliminary results. J. Natural Hazards, 55, 405-422.

Anabor, V., D. J. Stensrud, O. L. L. De Moraes, 2008: Serial upstream-propagating mesoscale convective system events over southeastern South America. Monthly Weather Review, 136, 3087-3105.

Serial mesoscale convective system (MCS) events with lifetimes over 18 h and up to nearly 70 h are routinely observed over southeastern South America from infrared satellite imagery during the spring and summer. These events begin over the southern La Plata River basin, with individual convective systems generally moving eastward with the cloud-layer mean wind. However, an important and common subset of these serial MCS events shows individual MCSs moving to the east or southeast, yet the region of convective development as a whole shifts upstream to the north or northwest. Analyses of the composite mean environments from 10 of these upstream-propagating serial MCS events using NCEP/NCAR reanalysis data events indicates that the synoptic conditions resemble those found in mesoscale convective complex environments over the United States. The serial MCS events form within an environment of strong low-level warm advection and strong moisture advection between the surface and 700 hPa from the Amazon region southward. One feature that appears to particularly influence the low-level flow pattern at early times is a strong surface anticyclone located just off the coast of Brazil. At upper-levels, the MCSs develop on the anticyclonic side of the entrance region to an upper-level jet. Mean soundings show that the atmosphere is moist from the surface to near 500 hPa, with values of convective available potential energy above 1200 J kg-1 at the time of system initiation. System dissipation and continued upstream propagation to the north and northwest occurs in tandem with a surface high pressure system that crosses the Andes Mountains from the west.

Anabor, V., D. J. Stensrud, O. L. De Moraes, 2009: Simulation of a serial upstream-propagating mesoscale convective system event over southeastern South America. Monthly Weather Review, 137, 2144-2163.

Serial upstream-propagating mesoscale convective system (MCS) events over southeastern South America are important contributors to the local hydrologic cycle as they can provide roughly half of the total monthly summer precipitation. However, the mechanisms of upstream propagation for these events have not been explored. To remedy this situation, a numerical simulation of the composite environmental conditions from 10 observed serial MCS events is conducted. Results indicate that the 3-day simulation from the composite yields a reasonable evolution of the large-scale environment and produces a large region of organized convection in the warm sector over an extended period as seen in observations. Upstream propagation of the convective region is produced and is tied initially to the development and evolution of untrapped internal gravity waves. However, as convective downdrafts develop and begin to merge and form a surface cold pool in the simulation, the cold pool and its interaction with the environmental low-level flow also begins to play a role in convective evolution. While the internal gravity waves and cold pool interact over a several hour period to control the convective development, the cold pool eventually dominates and determines the propagation of the convective region by the end of the simulation. This upstream propagation of a South American convective region resembles the southward burst convective events described over the United States and highlights the complex interactions and feedbacks that challenge accurate forecasts of convective system evolution.

Anderson, C. J., R. W. Arritt, J. S. Kain, 2007: An alternative mass flux profile in the Kain-Fritsch convective parameterization and its effect on seasonal precipitation.. J. Hydrometeor, 8, 1128-1140.

Baldwin, M. E., S. Lakshmivarahan, J. S. Kain, 2005: Development of an automated classification procedure for rainfall systems. Monthly Weather Review, 133, 844-862.

Baldwin, M. E., J. S. Kain, 2006: Sensitivity of Several Performance Measures to Displacement Error, Bias, and Event Frequency. Weather and Forecasting, 21, 636-648.

The sensitivity of various accuracy measures to displacement error, bias, and event frequency is analyzed for a simple hypothetical forecasting situation. Each measure is found to be sensitive to displacement error and bias, but probability of detection and threat score do not change as a function of event frequency. On the other hand, equitable threat score, true skill statistic, and odds ratio skill score behave differently with changing event frequency. A newly devised measure, here called the bias-adjusted threat score, does not change with varying event frequency and is reletively insensitive to bias. Numerous plots are presented to allow users of these accuracy measures to make quantitative estimates of sensitivities that are relevant to their particular application.

Available online at http://available soon from AMS.

Beida, R., M. W. Douglas, 2010: Developing high spatial resolution daytime cloud climatologies for Africa. Extended Abstracts, 29th Conference on Hurricanes and Tropical Meteorology, Tucson, AZ, USA, American Meteorological Society, P2.23.

MODIS visible imagery has been used to develop a short-period climatology of cloudiness for the African continent at approximately 250m spatial resolution. The MODIS imagery, from satellite overpasses at ~ 1030 and 1330 Local Time, are used to produce frequencies of visible clouds that provide a good estimate of mid-day cloudiness. Though our means fields are based on only about 5 years of data, they depict strong mesoscale controls on the mean cloudiness. Over much of Africa these controls are independent of season and are evident in the monthly means of any year. Most patterns can be explained as the effects of diurnally-driven circulations associated with sloping topography or land-water contrasts. Some regions with frequent cloudiness reflect the interaction of the prevailing winds with topography. This cloud climatology should be of value to all forecasters in Africa who wish to understand better their regional and local climatology.

Available online at http://ams.confex.com/ams/29Hurricanes/techprogram/MEETING.HTM.

Biggerstaff, M., L. Wicker, J. Guynes, C. Ziegler, J. Straka, E. Rasmussen, A. Doggett IV, L. Carey, J. Schroeder, C. Weiss, 2005: The Shared Mobile Atmospheric Research and Teaching Radar: A collaboration to enhance research and teaching. Bulletin of the American Meteorological Society, 86, .

Biggerstaff, M. I., D. R. MacGorman, W. D. Rust, C. Ziegler, J. M. Straka, T. J. Schuur, G. Carrie, K. Kuhlman, E. Rasmussen, P. Krehbiel, W. Rison, T. Hamlin, 2005: The role of storm dynamics on cloud electrification: The 29 May 2004 Tornadic Supercell Observed During TELEX. Preprints, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, 15R.1.

Biggerstaff, M. I., D. W. Burgess, G. D. Carrie, E. R. Mansell, L. J. Wicker, C. L. Ziegler, 2008: Storm-Scale Sampling Strategies for the Mobile C-Band Doppler Radars during VORTEX2. Extended Abstracts, 24th Conference on Severe Local Storms, Savannah, GA, USA, American Meteorological Society, 5.2.

Biggerstaff, M. I., D. P. Betten, C. L. Ziegler, D. R. McGorman, L. J. Wicker, D. W. Burgess, E. R. Mansell, 2010: Rear-flank downdraft dynamics in tornadic and non-tornadic supercell thunderstorms. Extended Abstracts, 25th Conference on Severe Local Storms, Denver, CO, USA, AMS, 8A.1.

Bodine, D., R. D. Palmer, C. Ziegler, P. L. Heinselman, 2010: High-resolution radar analysis during tornadogenesis from OU-PRIME on 10 May 2010. Extended Abstracts, 25th Conference on Severe Local Storms, Denver, CO, USA, Amer. Meteor. Soc., 15.4.

High-resolution polarimetric radar measurements in numerous supercells and tornadoes were obtained by the Polarimetric Radar for Innovations in Meteorology and Engineering (OU-PRIME) during the 10 May 2010 tornado outbreak. These observations include a supercell that produced an EF-4 tornado that developed near Moore, Oklahoma, only 10–15 km from OU-PRIME. The supercell's reflectivity appendage developed cyclonic curvature 15 min prior to the first tornado observations, coincident with an increase in low-level mesocyclone intensity and a protrusion of the rear-flank downdraft into the inflow region. Numerous cyclonic and anticyclonic flares were observed along the rear-flank downdraft (RFD) with cyclonic and anticyclonic rotation below 100 m, indicative of possible tornadoes or gustnadoes. As the RFD gust front extended further into the inflow region, vortices developed along the RFD gust front after a significant increase in near-surface convergence along the RFD gust front. In general, the vortex diameter and the spatial concentration both decreased as height increased.

To analyze the evolution of low-level rotation during tornadogenesis, single-radar approximations of vorticity and convergence in the RFD region are computed. Vorticity and convergence are computed using radial velocity differences between two gates over a fixed number of gates. The possible role of vorticity along the RFD gust front in tornadogenesis will be discussed, along with other vorticity sources identified in the analysis.

Available online at http://ams.confex.com/ams/25SLS/techprogram/paper_175834.htm.

Brooks, H. E., 2006: A global view of severe thunderstorms: Estimating the current distribution and possible future changes. Preprints, Symposium on the Challenges of Severe Convective Storms, Atlanta, GA, USA, American Meteorological Society, CD-ROM, J4.2.

Brooks, H. E., A. R. Anderson, K. Riemann, I. Ebbers, H. Flachs, 2007: Climatological aspects of convective parameters from the NCAR/NCEP reanalysis. Atmospheric Research, 83, 294-305.

Annual cycles of convectively important atmospheric parameters have been computed for a variety of from the National Center for Atmospheric Research (NCAR)/National Centers for Environmental Prediction (NCEP) global reanalysis, using 7 years of reanalysis data. Regions in the central United States show stronger seasonality in combinations of thermodynamic parameters than found elsewhere in North America or Europe. As a result, there is a period of time in spring and early summer when climatological mean conditions are supportive of severe thunderstorms.
The annual cycles help in understanding the large-scale processes that lead to the combination of atmospheric ingredients necessary for strong convection. This, in turn, lays groundwork for possible changes in distribution of the environments associated with possible global climate change.

Available online at http://www.nssl.noaa.gov/users/brooks/public_html/papers/ECSS2004.pdf.

Brooks, H. E., 2007: Development and use of climatologies of convective weather. Atmospheic Convection: Research and Operational Forecasting Aspects, D. B. Gaiotti, R. Steinacker, F. Stel, Ed(s)., SpringerWienNew York, 123-132.

Estimates of the occurrence (“climatologies”) of convective phenomena in time, space, and intensity can be useful in a variety of contexts. They provide background for forecasters, and the risk management and meteorological research communities. In part, because of the different needs of those user groups, caution must be applied when developing and using climatologies, especially if the intended application is outside of the original intent of the developers.

Brooks, H. E., 2007: Environmental conditions associated with convective phenomena: Proximity soundings. Atmospheic Convection: Research and Operational Forecasting Aspects, D. B. Gaiotti, R. Steinacker, F. Stel, Ed(s)., SpringerWeinNewYork, 113-122.

An important tool in understanding the relationship between environments and observed severe thunderstorm events are vertical profiles of environmental conditions collected in the vicinity of the storms. These relationships can help in the future forecasting of weather. In this paper, the use and cautions associated with these so-called proximity soundings are discussed.

Brooks, H. E., 2007: Ingredients-based forecasting. Atmospheric Convection: Research and Operational Forecasting Aspects, D. B. Gaiotti, R. Steinacker, Ed(s)., SpringerWienNew York, 133-140.

Forecasting the weather can be thought of as a problem in extracting a small signal from a noisy background field. Much information is available to the forecaster, but, frequently, only a small amount of that information is of importance for solving the forecast problem(s) of the day. As a result, an approach to forecasting must maximize the efficiency of the process. An effective way, particularly for hazardous weather, is to identify the ingredients required to produce a particular weather event and then to focus on the processes that can affect the presence of those ingredients. This allows the forecaster to narrow the range of aspects of the observations and model guidance that are considered during the forecast shift and, it is hoped, identify crucial developments as they occur.

Brooks, H. E., 2007: Practical Aspects of Forecasting Severe Convection in the United States: Environmental Conditions and Initiation. Atmospheic Convection: Research and Operational Forecasting Aspects, D. B. Gaiotti, R. Steinacker, F. Stel, Ed(s)., SpringerWienNew York, 141-148.

The first stage of forecasting convective weather involves forecasting the evolution of conditions that are favorable for the development of storms and their probable initiation. The scale of the forecasts are typically on the order of 100 km or larger and the lead time between the forecast and storms is 1-48 hours. In the United States, procedures have evolved so that the Storm Prediction Center of the National Weather Service has the responsibility for issuing these forecasts for the contiguous 48 states (the part of the US excluding Alaska and Hawaii.)

Brooks, H. E., 2007: Practical Aspects of Forecasting Severe Convection in the United States: Storm Evolution and Warning. Atmospheic Convection: Research and Operational Forecasting Aspects, D. B. Gaiotti, R. Steinacker, F. Stel, Ed(s)., SpringerWienNew York, 149-156.

In order to protect life and property, forecasts of severe convection are critical on short time and space scales (on the order of 1 hour or less and a few 10s of km or less). Accurate assessment of the environment and monitoring of high-resolution observational data, frequently focusing on radar-observed evolution, are essential in this process. In the United States, these short-term time and space scale forecasts are referred to as warnings and are prepared by local forecast offices of the National Weather Service, who have responsibility for forecasters on the order of 100,000 km2.

Brooks, H. E., C. A. Doswell III, D. Sutter, 2008: Low-Level Winds in Tornadoes and Potential Catastrophic Tornado Impacts in Urban Areas. Bulletin of the American Meteorological Society, 89, 87-90.

Brooks, H. E., N. Dotzek, 2008: The spatial distribution of severe convective storms and an analysis of their secular changes. Climate Extremes and Society, H. F. Diaz, Ed(s)., Cambridge University Press, 35-54.

Severe convective storms are responsible for billions of US dollars in damage each year around the world. They form an important part of the climate system by redistributing heat, moisture, and trace gases, as well as producing large quantities of precipitation.

Reporting of severe convection varies from country to country, however, so that determining their distribution from the reports alone is difficult, at best. Evidence does exist that the intensity of some events, particularly tornadoes, follows similar distributions in different locations, making it possible to build statistical models of occurrence. Remotely-sensed observations provide some insight, but the relationship between the observable parameters and the actual events of interest limits the quality of the estimate. Another approach is to use observations of the larger-scale environments.

As has been stated, the relationship between the observation and the event limits the estimate, but global coverage is possible. Time series of the favorable environments can also be developed from such data. In order to improve the estimates, the most pressing need is better observational data of events. Very few countries have formal systems for collection of severe thunderstorm reports. A new effort from a consortium of researchers in Europe to develop a continental-wide database offers the possibility of a significant improvement in data in that part of the world.

Brooks, H. E., 2008: Extreme Weather: Understanding the Science of Hurricanes, Tornadoes, Floods, Heat Waves, Snow Storms, Global Warming and Other Atmospheric Disturbances. EOS, Transactions American Geophysical Union, 89, 258-258.

Extreme weather is of importance because of the threats it makes to life and property. At the same time, extreme weather is a great fascination for meteorologists as well as for the general public. The conditions and processes that lead to extreme weather—although governed by the same physical principles as “ordinary” weather—frequently are far from the average state of the atmosphere. Thus, explaining them in simple terms can be difficult. This book represents an effort to explain the development of extreme weather to the public.

Brooks, H. E., 2009: Proximity soundings for severe convection for Europe and the United States from reanalysis data. Atmospheric Research, 93, 546-553.

Proximity soundings from reanalysis data have been created for significant severe thunderstorms in the United States and Europe, along with corresponding soundings not associated with severe thunderstorms. The probability of a combination of convective available potential energy (CAPE) and deep tropospheric wind shear being associated with significant severe thunderstorms has been calculated for both areas. Probabilities of significant severe storms are higher for high CAPE and shear in Europe, but those large scale environmental conditions are experienced much more frequently in the US, so that the overall number of events is much higher in the US. Probabilities of significant storms are approximately constant for constant values of CAPElow asteriskShear for each of the datasets. High values of 0–1 km wind shear and low lifted condensation levels are associated with higher probabilities that significant severe thunderstorms will be associated with significant tornadoes.

A subset of the US data, taken from the southeastern US in the cool season, produces probabilities that are much closer to the European values than the overall US data. The environments also are closer to European values with relatively low CAPE and low lifted condensation levels. From the southeastern US data, it is shown that the probability of severe convection occurring with moderate values of CAPElow asteriskShear is much higher in the cool season than in the warm season. It is suggested that the higher probabilities result from stronger synoptic forcing and stronger and more frequent boundaries to initiate convection.

Brooks, H. E., P. T. Marsh, A. M. Kowaleski, P. Groenemeijer, T. E. Thompson, C. S. Schwartz, C. M. Shafer, A. Kolodziej, N. Dahl, D. Buckey, 2011: Evaluation of European Storm Forecast Experiment (ESTOFEX) forecasts. Atmospheric Research, 100, 538-546.

Three years of forecasts of lightning and severe thunderstorms from the European Storm Forecast Experiment (ESTOFEX) have been evaluated. The forecasts exhibit higher quality in summer than in winter and there is some evidence that they have improved over the course of the evaluation. Five individual forecasters made the majority of the forecasts and differences in their forecasts are on the order of the overall variability of the forecast quality. As a result, the forecasts appear to come from a single unit, rather than from a group of individuals.
The graphical description of the probability of detection and frequency of hits recently developed by Roebber is a valuable tool for displaying the time series of lightning forecast performance. It also appears that, even though they are not intended for that purpose, using the lightning forecasts as a low-end forecast of severe thunderstorms is potentially useful for decision makers.

Available online at http://www.nssl.noaa.gov/users/brooks/public_html/papers/brooksetalestofex2011.pdf.

Brotzge, J., S. Erickson, H. Brooks, 2011: A five-year climatology of tornado false alarms. Weather and Forecasting, 26, 534-544.

During 2008 approximately 75% of tornado warnings issued by the National Weather Service (NWS) were false alarms. This study investigates some of the climatological trends in the issuance of false alarms and highlights several factors that impact false alarm ratio (FAR) statistics. All tornadoes and tornado warnings issued across the continental U.S. between 2000 and 2004 were analyzed, and the data were sorted by hour of the day, month of the year, geographical region and weather forecast office (WFO), the number of tornadoes observed on a day in which a false alarm was issued, distance of the warned area from the nearest NWS radar, county population density and county area.

Analysis of the tornado false alarm data identified six specific trends. First, the FAR was highest during non-peak storm periods, such as during the night and during the winter and late summer. Second, the FAR was strongly tied to the number of tornadoes warned per day. Nearly one-third of all false alarms were issued on days when no tornadoes were confirmed within the WFO’s county warning area. Third, the FAR varied with distance from radar, with significantly low estimates found beyond 150 km from radar. Fourth, the FAR varied with population density. For warnings within 50 km of a NWS radar, FAR increased with population density; however, for warnings beyond 150 km from radar, FAR decreased regardless of population density. Fifth, the FAR also varied as a function of county size. The FAR was generally highest for the smallest counties; the FAR was ~80% for all counties < 1000 km2 regardless of distance from radar. Finally, the combined effects of distance from radar, population density, and county size led to significant variability across geographic regions.

Brown, R. A., B. A. Flickinger, E. Forren, D. M. Schultz, D. Sirmans, P. L. Spencer, V. T. Wood, C. L. Ziegler, 2005: Improved detection of severe storms using experimental fine-resolution WSR-88D measurements. Weather and Forecasting, 20, 3-14.

NSSL Outstanding Scientific Paper Award

Doppler velocity and reflectivity measurements from WSR-88D (Weather Surveillance Radar - 1988 Doppler) radars provide important input to forecasters as they prepare to issue short-term severe storm and tornado warnings. Current-resolution data collected by the radars have an azimuthal spacing of 1.0° and range spacing of 1.0 km for reflectivity and 0.25 km for Doppler velocity and spectrum width. To test the feasibility of improving data resolution, National Severe Storms Laboratory's test-bed WSR-88D (KOUN) collected data in severe thunderstorms using 0.5° azimuthal spacing and 0.25 km range spacing,resulting in eight times the resolution for reflectivity and twice the resolution for Doppler velocity and spectrum width. Displays of current-resolution WSR-88D Doppler velocity and reflectivity signatures in severe storms were compared with displays showing finer-resolution signatures. At all ranges, fine-resolution data provided better depiction of severe storm characteristics. Eighty-five percent of mean rotational velocities derived from fine-resolution mesocyclone signatures were stronger than velocities derived from current-resolution signatures. Likewise, about 85% of Doppler velocity differences across tornado and tornadic vortex signatures were stronger than values derived from current-resolution data. In addition, low-altitude boundaries were more readily detected using fine-resolution reflectivity data. At ranges greater than 100 km, fine-resolution reflectivity displays revealed severe storm signatures, such as bounded weak echo regions and hook echoes, which were not readily apparent on current-resolution displays. Thus, the primary advantage of fine-resolution measurements over current-resolution measurements is the ability to detect stronger reflectivity and Doppler velocity signatures at greater ranges from a WSR-88D.

Brown, R. A., J. M. Lewis, 2005: Path to NEXRAD: Doppler radar development at the National Severe Storms Laboratory. Bulletin of the American Meteorological Society, 86, 1459-1470.

In this historical paper, we trace the scientific- and engineering-based steps at the National Severe Storms Laboratory (NSSL) and in the larger weather radar community that led to the development of NSSL's first 10-cm wavelength pulsed Doppler radar. This radar was the prototype for the current NEXRAD (NEXt generation weather RADar) or WSR-88D (Weather Surveillance Radar-1988 Doppler) Network.

We track events, both political and scientific, that led to the establishment of NSSL in 1964. The vision of NSSL's first director, Edwin Kessler, is reconstructed through access to historical documents and oral history. This vision included the development of Doppler radar where research was to be meshed with the operational needs of the U.S. Weather Bureau and its successor the National Weather Service.

Realization of the vision came through steps that were often fitful, where complications arose due to personnel concerns, and where there were always financial concerns. The historical research indicates that: (1) the engineering prowess and mentorship of Roger Lhermitte was at the heart of Doppler radar development at NSSL; (2) key decisions by Kessler in the wake of Lhermitte's sudden departure in 1967 proved crucial to the ultimate success of the project; (3) research results indicated that Doppler velocity signatures of mesocyclones are a precursor of damaging thunderstorms and tornadoes; and (4) results from field testing of the Doppler-derived products during the 1977-1979 Joint Doppler Operational Project -- especially the noticeable increase in the verification of tornado warnings and an associated marked decrease in false alarms -- led to the government decision to establish the NEXRAD network.

Buban, M. S., C. L. Ziegler, E. N. Rasmussen, Y. P. Richardson, 2007: The Dryline on 22 May 2002 during IHOP: Ground-Radar and In Situ Data Analyses of the Dryline and Boundary Layer Evolution. Monthly Weather Review, 135, 2473-2505.

On the afternoon and evening of 22 May 2002, high-resolution observations of the boundary layer (BL) and a dryline were obtained in the eastern Oklahoma and Texas panhandles during the International H2O Project. Using overdetermined multiple-Doppler radar syntheses in concert with a Lagrangian analysis of water vapor and temperature fields, the 3D kinematic and thermodynamic structure of the dryline and surrounding BL have been analyzed over a nearly 2-h period. The dryline is resolved as a strong (2–4 g/kg/km) gradient of water vapor mixing ratio that resides in a nearly north–south-oriented zone of convergence. Maintained through frontogenesis, the dryline is also located within a gradient of virtual potential temperature, which induces a persistent, solenoidally forced secondary circulation. Initially quasi-stationary, the dryline retrogrades to the west during early evening and displays complicated substructures including small wavelike perturbations that travel from south to north at nearly the speed of the mean BL flow. A second, minor dryline has similar characteristics to the first, but has weaker gradients and circulations. The BL adjacent to the dryline exhibits complicated structures, consisting of combinations of open cells, horizontal convective rolls, and transverse rolls. Strong convergence and vertical motion at the dryline act to lift moisture, and high-based cumulus clouds are observed in the analysis domain. Although the top of the analysis domain is below the lifted condensation level height, vertical extrapolation of the moisture fields generally agrees with cloud locations. Mesoscale vortices that move along the dryline induce a transient eastward dryline motion due to the eastward advection of dry air following misocyclone passage. Refractivity-based moisture and differential reflectivity analyses are used to help interpret the Lagrangian analyses.

Buban, M., C. L. Ziegler, E. N. Rasmussen, Y. Richardson, 2005: The structure and evolution of the dryline and surrounding boundary layer on 22 May 2002 during IHOP. Preprints, 11th Conference on Mesoscale Processes, Albuquerque, NM, USA, AMS, J6J.3.

Buban, M., C. Ziegler, Y. Richardson, 2008: Numerical simulations of the dryline and surrounding boundary layer on 22 May 2002 during IHOP. Extended Abstracts, 24th Conference on Severe Local Storms, Savannah, GA, USA, AMS, 18.4.

On the afternoon and evening of 22 May 2002, high-resolution data of the dryline and surrounding boundary layer (BL) were collected in the Oklahoma and Texas panhandles as part of the International H2O Project. Using over-determined multiple Doppler radar syntheses in concert with an innovative Lagrangian analysis technique, the 3-D kinematic and thermodynamic structure of the dryline and surrounding BL have been obtained over nearly a 2-hour period. A past study utilizing these analysis tools has delineated the 22 May dryline as a strong gradient of water vapor mixing ratio embedded in a zone of multi-Doppler radar-derived convergence. Misocyclones are observed to propagate from south to north along the dryline. The BL on both sides of the dryline exhibits complicated structures such as horizontal convective rolls, transverse rolls, and open convective cells.

In the present study, the time-varying radar and Lagrangian analyses have been used as initial and time-dependent lateral inflow boundary conditions to run high-resolution simulations of the dryline and BL. Simulations are conducted with the COllaborative Model for Multiscale Atmospheric Simulation (COMMAS), a 3-dimensional non-hydrostatic community cloud model which includes both short- and long-wave radiation, a force-restore surface physics parameterization, and a cloud microphysics parameterization. The simulations reproduce a nearly north-south oriented dryline with horizontal moisture and temperature gradients similar to observed values, as well as misocyclones, horizontal convective rolls, transverse rolls, and open convective cells. These simulated BL features are similar to analogous structures manifested in the observations and the Lagrangian analyses, although the modeled features are typically of higher spatial and temporal resolutions and may have larger amplitudes than the equivalent observed features. The simulated BL features are internally consistent with the model dynamics, with the high spatial and temporal resolution potentially permitting a better understanding of their evolution processes.

A feature of special interest are the misocyclones which develop and propagate northward along the dryline. Apparently forced in the simulations via longer wavelength undulations in the momentum and thermodynamic fields that are introduced at the lateral inflow boundaries, these perturbations collapse in scale and amplify into intense misovortices as they move downstream. The misocyclones act to modulate the moisture fields along the dryline, bringing larger moisture values westward ahead of and drier air eastward behind the misocyclone relative to its motion. The vertical motion within the deeper moist layer north of the misocyclone enhances simulated cumulus formation along and north of the axis of rotation.

The model simulations are compared to observations to qualitatively evaluate the strengths and weaknesses of the Lagrangian analyses. Aspects of the dryline circulation and other BL features are discussed along with their potential role in the convection initiation process.

Bukovsky, M. S., J. S. Kain, M. E. Baldwin, 2005: Bowing convective systems in a popular operational model: Are they for real. Preprints, 21st Conference on Weather Analysis and Forecasting/17th Conference on Numerical Weather Prediction, Washington, DC, USA, American Meteorological Society, 2A.1.

Bukovsky, M. S., J. S. Kain, M. E. Baldwin, 2006: Bowing Convective Systems in a Popular Operational Model: Are They for Real?. Weather and Forecasting, 21, 307-324.

Bowing, propagating precipitation features that sometimes appear in NCEP's North American Mesoscale model (NAM; formerly called the Eta Model) forecasts are examined. These features are shown to be associated with an unusual convective heating profile generated by the Betts–Miller–Janji convective parameterization in certain environments. A key component of this profile is a deep layer of cooling in the lower to middle troposphere. This strong cooling tendency induces circulations that favor expansion of parameterized convective activity into nearby grid columns, which can lead to growing, self-perpetuating mesoscale systems under certain conditions. The propagation characteristics of these systems are examined and three contributing mechanisms of propagation are identified. These include a mesoscale downdraft induced by the deep lower-to-middle tropospheric cooling, a convectively induced buoyancy bore, and a boundary layer cold pool that is indirectly produced by the convective scheme in this environment. Each of these mechanisms destabilizes the adjacent atmosphere and decreases convective inhibition in nearby grid columns, promoting new convective development, expansion, and propagation of the larger system. These systems appear to show a poor correspondence with observations of bow echoes on time and space scales that are relevant for regional weather prediction, but they may provide important clues about the propagation mechanisms of real convective systems.

Cao, J., Q. Xu, 2011: Computing Rossby potential vorticity in terrain-following coordinates. Monthly Weather Review, 139, 2955-2961.

Cao, J., Q. Xu, 2011: Computing streamfunction and velocity potential in a limited domain. Part II: Numerical methods and test experiments. Adv. Atmos. Sci., 28, 1445-1458.

Built on the integral formulas in Part I, numerical methods are developed for computing velocity potential and streamfunction in a limited domain. When there is no inner boundary (around a data hole) inside the domain, the total solution is the sum of the internally and externally induced parts. For the internally induced part, three numerical schemes (grid-staggering, local-nesting and piecewise continuous integration) are designed to deal with the singularity of the Green's function encountered in numerical calculations. For the externally induced part, by setting the velocity potential (or streamfunction) component to zero, the other component of the solution can be computed in two ways: (1) Solve for the density function from its boundary integral equation and then construct the solution from the boundary integral of the density function. (2) Use the Cauchy integral to construct the solution directly. The boundary integral can be discretized on a uniform grid along the boundary. By using local-nesting (or piecewise continuous integration), the scheme is refined to enhance the discretization accuracy of the boundary integral around each corner point (or along the entire boundary). When the domain is not free of data holes, the total solution contains a data-hole--induced part, and the Cauchy integral method is extended to construct the externally induced solution with irregular external and internal boundaries. An automated algorithm is designed to facilitate the integrations along the irregular external and internal boundaries. Numerical experiments are performed to evaluate the accuracy and efficiency of each scheme relative to others.

Case, J. L., S. R. Dembek, J. S. Kain, S. V. Kumar, T. Matsui, J. J. Shi, W. M. LaPenta, W. K. Tao, 2008: A sensitivity study of the operational NSSL WRF using unique NASA assets. Preprints, 9th Annual WRF Users' Workshop, Boulder, CO, USA, NCAR, P9.4.

Available online at http://www.mmm.ucar.edu/wrf/users/workshops/WS2008/abstracts/P9-04.pdf.

Clark, A. J., W. A. Gallus, M. Xue, F. Kong, 2010: Convection-allowing and Convection-parameterizing ensemble forecasts of a mesoscale convective vortex and associated severe weather environment. Weather and Forecasting, 25, 1052-1081.

Clark, A. J., W. A. Gallus, M. L. Weisman, 2010: Neighborhood-based verification of precipitation forecasts from convection-allowing NCAR WRF Model simulations and the operational NAM. Weather and Forecasting, 25, 1495-1509.

Clark, A. J., J. S. Kain, D. J. Stensrud, M. Xue, F. Kong, M. C. Coniglio, K. W. Thomas, Y. Wang, K. Brewster, J. Gao, X. Wang, S. J. Weiss, J. Du, 2011: Probabilistic precipitation forecast skill as a function of ensemble size and spatial scale in a convection-allowing ensemble. Monthly Weather Review, 139, 1410-1418.

Available online at http://journals.ametsoc.org/doi/pdf/10.1175/2010MWR3624.1.

Clark, A. J., S. J. Weiss, J. S. Kain, I. L. Jirak, M. C. Coniglio, C. J. Melick, C. Siewert, R. A. Sobash, P. T. Marsh, A. R. Dean, M. Xue, F. Kong, K. W. Thomas, Y. Wang, K. Brewster, J. Gao, X. Wang, J. Du, D. R. Novak, F. E. Barthold, M. J. Bodner, J. J. Levit, C. B. Entwistle, T. L. Jensen, J. C. Correia, 2012: An Overview of the 2010 Hazardous Weather Testbed Experimental Forecast Program Spring Experiment. Bulletin of the American Meteorological Society, 139, 55-74.

The NOAA Hazardous Weather Testbed (HWT) conducts annual spring forecasting experiments organized by the Storm Prediction Center and National Severe Storms Laboratory to test and evaluate emerging scientific concepts and technologies for improved analysis and prediction of hazardous mesoscale weather. A primary goal is to accelerate the transfer of promising new scientific concepts and tools from research to operations through the use of intensive real-time experimental forecasting and evaluation activities conducted during the spring and early summer convective storm period. The 2010 NOAA/HWT Spring Forecasting Experiment (SE2010), conducted 17 May through 18 June, had a broad focus, with emphases on heavy rainfall and aviation weather, through collaboration with the Hydrometeorological Prediction Center (HPC) and the Aviation Weather Center (AWC), respectively. In addition, using the computing resources of the National Institute for Computational Sciences at the University of Tennessee, the Center for Analysis and Prediction of Storms at the University of Oklahoma provided unprecedented real-time conterminous United States (CONUS) forecasts from a multimodel Storm-Scale Ensemble Forecast (SSEF) system with 4-km grid spacing and 26 members and from a 1-km grid spacing configuration of the Weather Research and Forecasting model. Several other organizations provided additional experimental high-resolution model output. This article summarizes the activities, insights, and preliminary findings from SE2010, emphasizing the use of the SSEF system and the successful collaboration with the HPC and AWC.

Cohen, A. E., M. C. Coniglio, S. F. Corfidi, S. J. Corfidi, 2006: Discrimination among non-severe, severe, and derecho-producing mesoscale convective system environments. Extended Abstracts, Severe Local Storms Symposium, 86th Amer. Meteor. Soc. Annual Meeting, Atlanta, GA, USA, American Meteorological Society, CD-ROM, P1.15. [Available from National Weather Center, 120 David L. Boren Blvd, Norman, OK, USA, 73071.]

Available online at http://ams.confex.com/ams/pdfpapers/103614.pdf.

Cohen, A. E., M. C. Coniglio, S. F. Corfidi, S. J. Corfidi, 2007: Discrimination of Mesoscale Convective System Environments Using Sounding Observations. Weather and Forecasting, 22, 1045-1062.

Cohn, S. J., J. Hallett, J. M. Lewis, 2006: Teaching graduate atmospheric measurement. Bulletin of the American Meteorological Society, 87, 1673-1678.

Coniglio, M. C., H. E. Brooks, S. J. Weiss, 2005: Use of proximity sounding parameters to improve the prediction of MCS speed and demise. 21st Conference on Weather Analysis and Forecasting, Washington, DC, USA, American Meteorological Society, 3.3.

Coniglio, M. C., D. J. Stensrud, L. J. Wicker, 2006: Effects of upper-level shear on the structure and maintenance of strong quasi-linear mesoscale convective systems. Journal of the Atmospheric Sciences, 63, 1231-1252.

Recent observational studies have shown that strong midlatitude mesoscale convective systems (MCSs) tend to decay as they move into environments with less instability and smaller deep-layer vertical wind shear. These observed shear profiles that contain significant upper-level shear are often different from the shear profiles considered to be the most favorable for the maintenance of strong, long-lived convective systems in some past idealized simulations. Thus, to explore the role of upper-level shear in strong MCS environments, a set of two-dimensional (2D) simulations of density currents within a dry, statically neutral environment is used to quantify the dependence of lifting along an idealized cold pool on the upper-level shear. A set of three-dimensional (3D) simulations of MCSs is produced to gauge the effects of the upper-level shear in a more realistic framework.

Results from the 2D experiments show that the addition of upper-level shear to a wind profile with weak to moderate low-level shear increases the vertical displacement of parcels despite a decrease in the vertical velocity along the cold pool interface. Parcels that are elevated above the surface (1–2 km) overturn and are responsible for the deep lifting in the deep-shear environments, while the surface-based parcels typically are lifted through the cold pool region in a rearward-sloping path. This deep overturning helps to maintain the leading convection and greatly increases the size and total precipitation output of the convective systems in more complex 3D simulations, even in the presence of 3D structures. These results show that the shear profile throughout the entire troposphere must be considered to gain a more complete understanding of the structure and maintenance of strong midlatitude MCSs.

Coniglio, M. C., S. F. Corfidi, 2006: Forecasting the speed and maintenance of severe mesoscale convective systems. Extended Abstracts, Severe Local Storms Symposium at the 86th AMS annual meeting, Atlanta, GA, USA, American Meteorological Society, CD-ROM, P1.30. [Available from National Weather Center, 120 David L. Boren Blvd, Norman, OK, USA, 73071.]

Available online at http://ams.confex.com/ams/pdfpapers/104815.pdf.

Coniglio, M. C., H. E. Brooks, S. F. Corfidi, S. J. Weiss, 2007: Forecasting the Maintenance of Quasi-Linear Mesoscale Convective Systems. Weather and Forecasting, 22, 556-570.

The problem of forecasting the maintenance of mesoscale convective systems (MCSs) is investigated through an examination of observed proximity soundings. Furthermore, environmental variables that are statistically different between mature and weakening MCSs are input into a logistic regression procedure to develop probabilistic guidance on MCS maintenance, focusing on warm-season quasi-linear systems that persist for several hours.
Between the mature and weakening MCSs, shear vector magnitudes over very deep layers are the best discriminators among hundreds of kinematic and thermodynamic variables. An analysis of the shear profiles reveals that the shear component perpendicular to MCS motion (usually parallel to the leading line) accounts for much of this difference in low levels and the shear component parallel to MCS motion accounts for much of this difference in mid-to-upper levels. The lapse rates over a significant portion of the convective cloud layer, the convective available potential energy, and the deep-layer mean wind speed are also very good discriminators and collectively provide a high level of discrimination between the mature and dissipation soundings as revealed by linear discriminant analysis. Probabilistic equations developed from these variables used with short-term numerical model output show utility in forecasting the transition of an MCS with a solid line of 50+ dbZ echoes to a more disorganized system with unsteady changes in structure and propagation. This study shows that empirical forecast tools based on environmental relationships still have the potential to provide forecasters with improved information on the qualitative characteristics of MCS structure and longevity. This is especially important since the current and near-term value added by explicit numerical forecasts of convection is still uncertain.

Coniglio, M. C., D. C. Dowell, L. J. Wicker, 2007: Ensemble Kalman filter assimilation of Doppler radar data: Analyses of a developing MCS. Extended Abstracts, 22nd Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, American Meteorlogical Society, 3B.3. [Available from Michael Coniglio, NSSL/FRDD, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Recent efforts at the National Severe Storms Laboratory and the University of Oklahoma/Center for Analysis and Prediction of Storms have shown the positive impact of assimilating real Doppler velocity and reflectivity observations using an Ensemble Kalman Filter (EnKF) technique for the storm-scale analysis of supercell thunderstorms. Recently, the utility of this technique to other convective modes with multiple updrafts and more complex evolutions has been shown with analyses of the 16-17 June 2005 severe bow echo MCS across Oklahoma. It is well known that an accurate depiction of convective system cold pools is a prerequisite for the accurate short-term (1-12 h) prediction of MCSs by high-resolution numerical models. One of the most promising aspects of the analysis is the detailed and accurate depiction of the cold convective outflow and the robustness of the analyses to changes in the experimental design (although the well-known sensitivity to microphysics is still apparent). This talk will highlight the successful analysis of this event and discuss the mechanics of the EnKF procedure applied to a real and complex convective situation. In addition, the relative merits of 1-h forecasts produced from the EnKF analyses and the many outstanding issues that need to be addressed before these techniques can be applied in real time will be discussed.

Available online at http://ams.confex.com/ams/pdfpapers/124285.pdf.

Coniglio, M. C., J. S. Kain, S. J. Weiss, M. Xue, M. L. Weisman, Z. I. Janjic, 2007: Evaluating storm-scale model output for severe-weather forecasting: The 2007 NOAA HWT Spring Experiment.. Preprints, 4th European Conference on Severe Storms, Trieste, Italy, International Centre for Theoretical Physics, CD-ROM, 03.11.

Coniglio, M. C., A. E. Cohen, S. F. Corfidi, S. J. Corfidi, 2007: Discrimination of MCS environments using sounding observations. Weather and Forecasting, 22, 1045-1062.

The prediction of the strength of mesoscale convective systems (MCSs) is a major concern to operational meteorologists and the public. To address this forecast problem, this study examines meteorological variables derived from sounding observations taken in the environment of quasi-linear MCSs. A set of 186 soundings that sampled the beginning and mature stages of the MCSs are categorized by their production of severe surface winds into weak, severe, and derecho-producing MCSs. Differences in the variables among these three MCS categories are identified and discussed. Mean low- to upper-level wind speeds and deep-layer vertical wind shear, especially the component perpendicular to the convective line, are excellent discriminators among all three categories. Low-level inflow relative to the system is found to be an excellent discriminator, largely because of the strong relationship of system severity to system speed. Examination of the mean wind and shear vectors relative to MCS motion suggests that cell propagation along the direction of cell advection is a trait that separates severe, long-lived MCSs from the slower-moving, nonsevere variety and that this is favored when both the deep-layer shear vector and the mean deep-layer wind are large and nearly parallel. Midlevel environmental lapse rates are found to be very good discriminators among all three MCS categories, while vertical differences in equivalent potential temperature and CAPE only discriminate well between weak and severe/derecho MCS environments. Knowledge of these variables and their distribution among the different categories of MCS intensity can be used to improve forecasts and convective watches for organized convective wind events.

Coniglio, M. C., J. S. Kain, S. J. Weiss, D. R. Bright, J. J. Levit, M. Xue, M. L. Weisman, Z. I. Janjic, M. Pyle, J. Du, D. J. Stensrud, 2007: Evaluating WRF model output for severe-weather forecasting: The 2007 NOAA HWT Spring Experiment.. Extended Abstracts, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, American Meteorological Society, CD-ROM, 11A.2.

Coniglio, M. C., M. Bardon, K. Virts, S. J. Weiss, 2006: Forecasting the maintenance of mesoscale convective systems.. Extended Abstracts, 23rd Conf. on Severe Local Storms, St. Louis, MO, USA, American Meteorological Society, CD-ROM, 2.3.

Coniglio, M. C., J. S. Kain, S. J. Weiss, D. R. Bright, J. J. Levit, G. W. Carbin, K. W. Thomas, F. Kong, M. Xue, M. L. Weisman, M. E. Pyle, K. L. Elmore, 2008: Evaluation of WRF model output for severe-weather forecasting from the 2008 NOAA Hazardous Weather Testbed Spring Experiment. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., CD-ROM, 12.4. [Available from Michael C. Coniglio, NSSL, 120 David L. Boren Blvd., Norman, OK, USA, 73072.]

Available online at http://ams.confex.com/ams/24SLS/techprogram/paper_142060.htm.

Coniglio, M. C., K. L. Elmore, J. S. Kain, S. J. Weiss, M. Xue, M. L. Weisman, 2010: Evaluation of WRF model output for severe weather forecasting from the 2008 NOAA Hazardous Weather Testbed Spring Experiment. Weather and Forecasting, 25, 408-427.

This study assesses forecasts of the preconvective and near-storm environments from the convectionallowing
models run for the 2008 National Oceanic and Atmospheric Administration (NOAA) Hazardous
Weather Testbed (HWT) spring experiment. Evaluating the performance of convection-allowing models
(CAMs) is important for encouraging their appropriate use and development for both research and operations.
Systematic errors in theCAMforecasts included a cold bias in mean 2-m and 850-hPa temperatures over most
of the United States and smaller than observed vertical wind shear and 850-hPa moisture over the high plains.
The placement of airmass boundaries was similar in forecasts from the CAMs and the operational North
American Mesoscale (NAM) model that provided the initial and boundary conditions. This correspondence
contributed to similar characteristics for spatial and temporalmean error patterns. However, substantial errors
were found in the CAM forecasts away from airmass boundaries. The result is that the deterministic CAMs
do not predict the environment as well as the NAM. It is suggested that parameterized processes used at
convection-allowing grid lengths, particularly in the boundary layer, may be contributing to these errors.
It is also shown that mean forecasts from an ensemble of CAMs were substantially more accurate than
forecasts from deterministic CAMs. If the improvement seen in the CAM forecasts when going from a deterministic
framework to an ensemble framework is comparable to improvements in mesoscale model forecasts
when going from a deterministic to an ensemble framework, then an ensemble of mesoscale model
forecasts could predict the environment even better than an ensemble of CAMs. Therefore, it is suggested that
the combination of mesoscale (convection parameterizing) andCAMconfigurations is an appropriate avenue
to explore for optimizing the use of limited computer resources for severe weather forecasting applications.

Coniglio, M. C., J. Y. Hwang, D. J. Stensrud, 2010: Environmental Factors in the Upscale Growth and Longevity of MCSs Derived from Rapid Update Cycle Analyses. Monthly Weather Review, 138, 3514-3539.

Composite environments of mesoscale convective systems (MCSs) are produced from Rapid Update Cycle (RUC) analyses to explore the differences between rapidly- and slowly-developing MCSs as well as the differences ahead of long-lived and short-lived MCSs. The composite analyses capture the synoptic-scale features known to be associated with MCSs and depict the inertial oscillation of the nocturnal low-level jet (LLJ), which remains strong but tends to veer away from decaying MCSs. The composite first-storms environment for the rapidly-developing MCSs contains a stronger LLJ located closer to the first storms region, much more conditional instability, potential instability, and energy available for downdrafts, smaller 3 – 10 km vertical wind shear, and smaller geostrophic potential vorticity in the upper troposphere, when compared to the environment for the slowly-developing MCSs. The weaker shear above 3 km for the rapidly-developing MCSs is consistent with supercell or discrete cell modes being less likely in weaker deep layer shear and the greater potential for a cold pool to trigger convection when the shear is confined to lower levels. Furthermore, these results suggest that low values of upper-level potential vorticity may signal a rapid transition to an MCS. The composite environment ahead of the genesis of long-lived MCSs contains a broader LLJ, a better-defined frontal zone, stronger low-level frontogenesis, deeper moisture and stronger wind shear above 2 km, when compared to short-lived MCSs. The larger shear above 2 km for the long-lived MCSs is consistent with the importance of shear elevated above the ground to help organize and maintain convection that feeds on the elevated unstable parcels after dark and is indicative of the enhanced baroclinicity ahead of the MCSs.

Coniglio, M. C., S. F. Corfidi, J. S. Kain, 2011: Environment and Early Evolution of the 8 May 2009 Derecho-Producing Convective System. Monthly Weather Review, 139, 1083-1102.

This study documents the complex environment and early evolution of the remarkable derecho that traversed portions of the central United States on 8 May 2009. Central to this study is the comparison of the 8 May 2009 derecho environment to that of other mesoscale convective systems (MCSs) that occurred in the central United States during a similar time of year. Synoptic-scale forcing was weak and thermodynamic instability was limited during the development of the initial convection, but several mesoscale features of the environment appeared to contribute to initiation and upscale growth, including a mountain wave, a midlevel jet streak, a weak midlevel vorticity maximum, a “Denver cyclone,” and a region of upper-tropospheric inertial instability.

The subsequent MCS developed in an environment with an unusually strong and deep low-level jet (LLJ), which transported exceptionally high amounts of low-level moisture northward very rapidly, destabilized the lower troposphere, and enhanced frontogenetical circulations that appeared to aid convective development. The thermodynamic environment ahead of the developing MCS contained unusually high precipitable water (PW) and very large midtropospheric lapse rates, compared to other central plains MCSs. Values of downdraft convective available potential energy (DCAPE), mean winds, and 0–6-km vertical wind shear were not as anomalously large as the PW, lapse rates, and LLJ. In fact, the DCAPE values were lower than the mean values in the comparison dataset. These results suggest that the factors contributing to updraft strength over a relatively confined area played a significant role in generating the strong outflow winds at the surface, by providing a large volume of hydrometeors to drive the downdrafts.

Coniglio, M. C., J. Y. Hwang, D. J. Stensrud, 2011: CORRIGENDUM. Monthly Weather Review, 139, 2686-2688.

Coniglio, M. C., S. F. Corfidi, J. S. Kain, 2012: Views on Applying RKW Theory: An Illustration Using the 8 May 2009 Derecho-Producing Convective System. Monthly Weather Review, 140, 1023-1043.

This work presents an analysis of the vertical wind shear during the early stages of the remarkable 8 May 2009 central U.S. derecho-producing convective system. Comments on applying Rotunno–Klemp–Weisman (RKW) theory to mesoscale convective systems (MCSs) of this type also are provided. During the formative stages of the MCS, the near-surface-based shear vectors ahead of the leading convective line varied with time, location, and depth, but the line-normal component of the shear in any layer below 3 km ahead of where the strong bow echo developed was relatively small (6–9 m s−1). Concurrently, the midlevel (3–6 km) line-normal shear component had magnitudes mostly >10 m s−1 throughout.

In a previous companion paper, it was hypothesized that an unusually strong and expansive low-level jet led to dramatic changes in instability, shear, and forced ascent over mesoscale areas. These mesoscale effects may have overwhelmed the interactions between the cold pool and low-level shear that modulate system structure in less complex environments. If cold pool–shear interactions were critical to producing such a strong system, then the extension of the line-normal shear above 3 km also appeared to be critical. It is suggested that RKW theory be applied with much caution, and that examining the shear above 3 km is important, if one wishes to explain the formation and maintenance of intense long-lived convective systems, particularly complex nocturnal systems like the one that occurred on 8 May 2009.

Corfidi, S. F., S. J. Weiss, J. S. Kain, S. J. Corfidi, R. M. Rabin, J. L. Levit, 2010: Revisiting the 3-4 April 1974 super outbreak of tornadoes. Weather and Forecasting, 25, .

The Super Outbreak of tornadoes over the central and eastern United States on 3–4 April 1974 remains the most outstanding severe convective weather episode on record in the continental United States. The outbreak far surpassed previous and succeeding events in severity, longevity, and extent. In this paper, surface, upper-air, radar, and satellite data are used to provide an updated synoptic and subsynoptic overview of the event. Emphasis is placed on identifying the major factors that contributed to the development of the three main convective bands associated with the outbreak, and on identifying the conditions that may have contributed to the outstanding number of intense and long-lasting tornadoes. Selected output from a 29-km, 50-layer version of the Eta forecast model, a version similar to that available operationally in the mid-1990s, also is presented to help depict the evolution of thermodynamic stability during the event.

Dawson II, D. T., M. Xue, J. A. Milbrandt, M. K. Yau, 2010: Comparison of Evaporation and Cold Pool Development between Single-Moment and Multimoment Bulk Microphysics Schemes in Idealized Simulations of Tornadic Thunderstorms. Monthly Weather Review, 138, .

Idealized simulations of the 3 May 1999 Oklahoma tornadic supercell storms are conducted at various horizontal grid spacings ranging from 1 km to 250 m, using a sounding extracted from a prior 3-km grid spacing real-data simulation. A sophisticated multimoment bulk microphysics parameterization scheme capable of predicting up to three moments of the particle or drop size distribution (DSD) for several liquid and ice hydrometeor species is evaluated and compared with traditional single-moment schemes. The emphasis is placed on the impact of microphysics, specifically rain evaporation and size sorting, on cold pool strength and structure, and on the overall reflectivity structure of the simulated storms. It is shown through microphysics budget analyses and examination of specific processes within the low-level downdraft regions that the multimoment scheme has important advantages, which lead to a weaker and smaller cold pool and better reflectivity structure, particularly in the forward-flank region of the simulated supercells. Specifically, the improved treatment of evaporation and size sorting, and their effects on the predicted rain DSDs by the multimoment scheme helps to control the cold bias often found in the simulations using typical single-moment schemes. The multimoment results are more consistent with observed (from both fixed and mobile mesonet platforms) thermodynamic conditions within the cold pools of the discrete supercells of the 3 May 1999 outbreak.

Diffenbaugh, N. S., R. J. Trapp, H. E. Brooks, 2008: Does Global Warming Influence Tornado Activity?. EOS, TRANSACTIONS, AMERICAN GEOPHYSICAL UNION, 89, 533-534.

Tornadoes and other severe thunderstorm phenomena frequently cause as much annual property damage in the United States as do hurricanes, and often cause more fatalities (see http://www.nws.noaa.gov/om/hazstats.shtml). In 2008, there were 2176 preliminary tornado reports logged through mid-December, with 1600 “actual counts” (duplicate reports removed) through September, the highest total in the past half century (Figure 1). The mass media have covered these events extensively, and experts have been deluged with requests for explanations, including possible links to anthropogenic global warming. Although recent research has yielded insight into the connections between global warming and tornado and severe thunderstorm forcing, these relationships remain mostly unexplored, largely because of the challenges in observing and numerically simulating tornadoes. Indeed, a number of questions that have been answered for other climate-related phenomena remain particularly difficult for climate and severe weather scientists, including whether there are detectable trends in tornado occurrence and if so, what causes them. This article explores the challenges and opportunities in pursuing these areas of research.

Available online at http://www.agu.org/journals/eo/eo0853/2008EO530001.pdf.

Dodson, A., S. Van Cooten, K. Howard, J. Zhang, X. Xu, 2008: Assessing Vertical Profiles of Reflectivity (VPR's) To Detect Extreme Rainfall: Implications for Flash Flood Monitoring and Prediction. Preprints, 22nd Conference on Hydrology- Session 1, Weather To Climate Scale Hydrological Forecasting, New Orleans, LA, USA, AMS, CD-ROM, 1.5.

Tropical Storm Barry moved across the state of Florida from Tampa to Jacksonville on June 2 and then became extratropical as it moved northeast along the coastlines of Georgia, South Carolina and North Carolina from June 3 to June 4, 2007. Rainfall reports from gauges located within the surveillance areas of the Wakefield, Virginia (AKQ), Raleigh-Durham, North Carolina (RDU), and Morehead City, North Carolina (MHX), NEXRAD sites were collected and processed to document hourly rainfall rates associated with the system. In addition to the gauge data, atmospheric soundings from six area upper air observing sites were archived and analyzed to determine the response of atmospheric conditions, specifically freezing level, precipitable water, and atmospheric instability, as the system affected the region.

NOAA's National Severe Storms Laboratory (NSSL) Q2 System (www. nmq.nssl.noaa.gov) produces Vertical Profiles of Reflectivity (VPR) every five minutes for each continental United States (CONUS) NEXRAD site. These VPRs are used in the production of five-minute multi-sensor Quantitative Precipitation Estimates (QPE) to provide constantly updated relationships between radar reflectivity factor, Z, and rain rate, R (Z-R). VPRs were archived for June 3 and 4 for AKQ, RDU, and MHX. The VPRs were analyzed to quantify radar reflectivity trends over the course of the storm event. These trends were then correlated with rainfall rates, atmospheric sounding data, and surface observations, to investigate the characteristics of the VPRs associated with the highest rainfall rates. Results of this analysis indicate VPRs associated with the highest hourly rainfall rates observed with the storm system occurred as VPRs lost a concentrated area of high reflectivities around the atmospheric freezing level. Additionally, the gradient of radar reflectivities above and below this dissipating high reflectivity area diminished. Atmospheric soundings and surface map analysis indicated the air mass characteristics were acquiring tropical characteristics as surface dew points and atmospheric water content were increasing, wind directions transitioned from westerly to an easterly fetch off the Atlantic Ocean, and the atmospheric freezing level was rising. As the storm system moved away from the Carolinas, VPRs began to regain a concentrated area of high reflectivities around the atmospheric freezing level and the gradient of radar reflectivities began to increase once again above and below the area of higher reflectivities.

To quantify the implications of these VPR characteristics on the accuracy of the Q2 system's five-minute multi-sensor Quantitative Precipitation Estimates (QPE), the Q2 statistical verification tools were used to evaluate the performance of the system during the periods of the most intense rainfall. The Q2 system has recently implemented a tropical rain Z-R when VPRs and atmospheric sounding data meet criteria which have been identified by NSSL scientists as common factors in intense rainfall events. The VPRs observed through this June, 2007 storm event, were consistent with their findings. Results of this assessment show the Q2 tropical Z-R relationship produced highly accurate precipitation estimates which are available at a 1 km grid mesh resolution every five minutes. Additionally, the dynamic VPR system captured the air mass changes which occurred during the event. This feature provides improved information on a storm's environment to determine appropriate radar Z-R adjustments. This case demonstrates the ability to increase the accuracy of precipitation estimates especially in ungauged locations which can improve NOAA and our nation's flash flood monitoring and prediction programs.

Available online at http://ams.confex.com/ams/88Annual/techprogram/paper_135143.htm.

Doswell III, C. A., H. E. Brooks, M. P. Kay, 2005: Climatological estimates of daily local nontornadic severe thunderstorm probability for the United States. Weather and Forecasting, 20, 577-595.

The probability of nontornadic severe weather event reports near any location in the United States for any day of the year has been estimated. Gaussian smoothers in space and time have been applied to the observed record of severe thunderstorm occurrence from 1980 to 1994 to produce daily maps and annual cycles at any point. Many aspects of this climatology have been identified in previous work, but the method allows for the consideration of the record in several new ways. A review of the raw data, broken down in various ways, reveals that numerous nonmeteorological artifacts are present in the raw data. These are predominantly associated with the marginal nontornadic severe thunderstorm events, including an enormous growth in the number of severe weather reports since the mid-1950s. Much of this growth may be associated with a drive to improve warning verification scores. The smoothed spatial and temporal distributions of the probability of nontornadic severe thunderstorm events are presented in several ways. The distribution of significant nontornadic severe thunderstorm reports (wind speeds 65 kt and/or hailstone diameters 2 in.) is consistent with the hypothesis that supercells are responsible for the majority of such reports.

Doswell III, C. A., H. E. Brooks, N. Dotzek, 2009: On the implementation of the enhanced Fujita scale in the USA. Atmospheric Research, 93, 554-563.

The history of tornado intensity rating in the United States of America (USA), pioneered by T. Fujita, is reviewed, showing that non-meteorological changes in the climatology of the tornado intensity ratings are likely, raising questions about the temporal (and spatial) consistency of the ratings. Although the Fujita scale (F-scale) originally was formulated as a peak wind speed scale for tornadoes, it necessarily has been implemented using damage to estimate the wind speed. Complexities of the damage-wind speed relationship are discussed.

Recently, the Fujita scale has been replaced in the USA as the official system for rating tornado intensity by the so-called Enhanced Fujita scale (EF-scale). Several features of the new rating system are reviewed and discussed in the context of a proposed set of desirable features of a tornado intensity rating system.

It is concluded that adoption of the EF-scale in the USA may have been premature, especially if it is to serve as a model for how to rate tornado intensity outside of the USA. This is in large part because its degree of damage measures used for estimating wind speeds are based on USA-specific construction practices. It is also concluded that the USA's tornado intensity rating system has been compromised by secular changes in how the F-scale has been applied, most recently by the adoption of the EF-scale. Several recommendations are offered as possible ways to help develop an improved rating system that will be applicable worldwide.

Doswell III, C. A., G. W. Carbin, H. E. Brooks, 2012: The tornadoes of spring 2011 in the USA: an historical perspective. Weather, 67, 88-94.

No abstract

Douglas, M., J. M. Galvez, J. F. Mejia, C. Brown, R. Orozco, C. Watts, 2005: Seasonal evolution of the sea-land breeze circulation and its role in the precipitation climatology of northwestern Mexico. Preprints, 6th Conference on Coastal Atmospheric and Oceanic Prediction and Processes (6COASTAL), San Diego, CA, USA, American Meteorological Society, CD-ROM, 3.7.

Douglas, M. W., J. Mejia, J. Murillo, R. Orozco, 2007: Spatial Structure of Cloudiness Associated with the Mid-Summer Drought from MODIS and GOES Imagery. Extended Abstracts, AGU Joint Assembly, Acapulco, Mexico, AGU, H51G-04.

Douglas, M. W., R. Orozco, J. F. Mejia, 2008: Mapping the spatial extent of the Central American mid-summer drought with MODIS and GOES imagery. Preprints, 28th Conference on Hurricanes and Tropical Meteorology, Orlando, FL, USA, American Meteorological Society, P1C.10. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Many parts of Central America and southern Mexico experience an extended dry period within the longer period of summer rains. This mid-summer drought (MSD), usually during July and August, shows a complicated spatial structure, reflecting the interaction of the large-scale synoptic flow and the varied topography of the region. We have used MODIS imagery (250 m resolution) and GOES 10 km imagery for the years 1983 to 2006 to describe the spatial structure of the cloudiness associated with the MSD. Compositing results using specific periods and also by using different indices (trade wind intensity and cloudiness over specific domains) will be shown. The importance (and challenge) of identifying suitable indices that represent the MSD will be discussed.

Douglas, M. W., J. F. Mejia, 2008: Aircraft measurements of temperature anomalies associated with tropical waves during NAMMA. Preprints, 28th Conference on Hurricanes and Tropical Meteorology, Orlando, FL, USA, American Meteorological Society, P1E.4. [Available from Michael W Douglas, 120, Norman, OK, USA, 73072.]

Special measurements were made of tropical waves over the far eastern tropical Atlantic during the NASA-AMMA field program during August and September 2006. One objective of this program was to help determine why some waves develop rapidly into tropical storms while most do not. This presentation shows the temperature anomalies associated with the different waves sampled by the dropsonde and flight level data from the NASA DC-8 and also other estimates of the temperature field from in-situ soundings. The analyses will be compared both with operational global analyses and with mesoscale analyses produced by assimilating the aircraft observations with the WRF model.

Douglas, M. W., J. F. Mejia, R. Orozco, S. Henry, 2008: Quantifying the extent and degree of cloud-affected tropical environments with MODIS imagery. Two extreme environments: Lomas and cloud forests. Preprints, 28th Conference on Hurricanes and Tropical Meteorology, Orlando, FL, USA, American Meteorological Society, 10.1. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Quantifying the extent and degree of cloud-affected tropical environments with MODIS imagery. Two extreme environments: Lomas and cloud forests

Michael W. Douglas, NOAA/NSSL, Norman, OK; and J. F. Mejia, R. Orozco, and S. Henry

Using a simple algorithm for extracting cloudiness from the visible MODIS imagery we have developed short-period (~ several years) cloudiness climatologies for different tropical regions at 250m spatial resolution. This presentation focuses on two environments that are difficult to accurately delineate with conventional climate data or even current satellite-based rainfall estimation techniques. One such environment, tropical cloud forest, is characterized by very high precipitation and also high cloudiness. However, cloud forest is mostly distinguished from surrounding lowland rain forest by the very high frequency of cloudiness and its small spatial extent. The second environment of our study is the coastal fog/low cloud zone along arid coastlines (known as “lomas” in Peru). These regions receive almost no rainfall, yet have vegetation supported by the frequent low clouds that intercept the topography along the coast. Such areas are even more difficult to identify from raingauges or satellite rainfall estimates than cloud forests.

We have developed a simple algorithm to use the cloudiness frequencies obtained from the MODIS imagery to classify the “intensity” of both the cloud forests and the lomas. The algorithm uses MODIS imagery from the NASA Terra and Aqua satellites to stratify cloudiness by annual amount, seasonality, and diurnal variability. Areas most favorable for vegetation growth are those with maximum annual frequency of cloudiness and minimum seasonality and diurnal variation, other factors being equal.S

Douglas, M. W., J. F. Mejia, J. F. Galvez, J. Murillo, R. Orozco, 2008: West African pilot balloon network during the NAMMA-2006 and implications for the future of the African pilot balloon sounding network.. Preprints, The 88th Annual Meeting (20-24 January 2008) (New Orleans, LA), New Orleans, LA, USA, American Meteorological Society, 15B.5. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

The West African pilot balloon network during the NAMMA-2006 and implications for the future of the African pilot balloon sounding network

Michael W. Douglas, NOAA/NSSL, Norman, OK; and J. Murillo, J. F. Mejia, J. M. Galvez, and R. Orozco

The pilot balloon network in West Africa has been in place for more than 50 years, and in the past the network was characterized by relatively frequent observations (often 4-times daily) and with high spatial density (more than 20 stations in West Africa). Such a network would be potentially very useful in helping to track the African waves that typically evolve into tropical storms over the Atlantic Ocean. However, the pilot balloon network has decayed in recent decades. The NAMMA (NASA-African Monsoon Multidisciplinary Analysis (AMMA)), involving a field campaign in 2006, afforded an opportunity to attempt to re-invigorate the pilot balloon network. One component of NAMMA involved strengthening the pilot balloon wind sounding network over west Africa to help describe the intensity of African waves exiting the continent. Four countries were the focus of this work and 10 stations were visited over the course of one month just prior to the NAMMA. Many technical problems were encountered and dealt with, but many problems were related to the personnel and the organization of the National Meteorological Services of the region. Some success was achieved in making the observations, but considerably less than was initially expected. This talk summarizes the main problems encountered, our short-term solutions, and our perspectives on how renovating this potentially-valuable network may be possible.

Douglas, M. W., J. M. Murillo, R. K. Orozco, J. F. Mejias, 2008: Underutilized observations for studying tropical climate variations: the historical pilot balloon database.. Preprints, The 88th Annual Meeting (20-24 January 2008) (New Orleans, LA), New Orleans, LA, USA, American Meteorological Organization, 3B.6. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Underutilized observations for studying tropical climate variations: the historical pilot balloon data base

Michael W. Douglas, NOAA/NSSL, Norman, OK; and R. Orozco, J. F. Mejia, and J. Murillo

The longest-running atmospheric sounding data base is that from pilot balloon observations (“pibals”), whose routine observations date from the early 20th century. Such observations are still made today, though mostly in developing countries in Asia and Africa. Although pibals are subject to limitations (cloudiness and darkness being the two most obvious ones), their low cost has historically allowed for more frequent and more widespread use than radiosondes. Much less well-known, and less appreciated, is that pibals have some advantages over radiosonde winds for studies of climate variability. The procedure for making a pibal has not fundamentally changed in 100 years, unlike wind observations obtained from rawinsonde systems – which have used radiotheodolites, Omega, LORAN and now GPS. Wind profiles obtained from these different systems show somewhat differing characteristics, which can complicate identifying historical trends in wind data.

Making effective use of historical pilot balloon data for climate studies requires availability of the original angle data and some metadata - such as the characteristics of the balloons and inflation procedures. We discuss the difficulty in obtaining both of these; a major effort at digitizing the global data base of pilot balloon observations will be required. Studies are underway (results will be shown) to evaluate the uncertainties introduced into mean wind profiles due to missing data (generally due to clouds), and the observational errors that characterize different pibal networks. These need to be known to determine the limitations of pibals for describing and monitoring regional climate variations.

Douglas, M. W., J. Murillo, J. F. Mejia, 2008: Two courses missing from meteorology programs at US universities.. Preprints, The 88th Annual Meeting (20-24 January 2008) (New Orleans, LA), New Orleans, LA, USA, American Meteorological Society, P1.35. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Two courses missing from US university meteorology programs

Michael W. Douglas, NOAA/NSSL, Norman, OK; and J. Murillo and J. F. Mejia

This presentation describes the need for, and potential content of, two meteorological courses usually lacking in meteorology programs at US universities. These subjects are somewhat related and potentially could be combined into one course. The first subject is that of “Design and execution of field programs in the atmospheric sciences”. While it might be argued that there is such diversity in meteorological field activities that “hands-on” learning is best, there are many aspects common to most field studies that students could benefit from via formal lectures. Such a course might best be taught at the advanced graduate level, where students are closer to participating in, and perhaps helping design, such activities. The second, somewhat complementary course, might be titled “International Meteorological Activities and the functions of National Meteorological Services”. Rarely are US students (unlike foreign students) exposed to the enormous variety of meteorological activities that occur globally. An equally small number of students have a good conceptual understanding of the different components of any National Meteorological Service (including that of the US). Material common to both courses would include covering the existing (and research) observing systems across the globe – this material is often left out of courses on meteorological instrumentation.

Motivation for developing this material has come from the development of courses for international audiences with widely varying backgrounds. A sample syllabus will be provided to stimulate discussion.

Douglas, M. W., J. Murillo, R. Orozco, J. M. Galvez, J. F. Mejia, 2006: Accuracy of the Aviation Model (AVN) final analyses over Central South America based upon upper air observations collected during the SALLJEX.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, AMS, PC1-24.

Douglas, M. W., J. M. Galvez, C. R. Reyes, R. Orozco, 2006: Observed diurnal circulations and rainfall over the altiplano during the SALLJEX.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PA1-9.

Douglas, M. W., J. M. Galvez, 2006: Modulation of rainfall by Lake Titicaca using the WRF Model.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PB1-21.

Douglas, M. W., J. M. Galvez, 2006: Northward-propagating surges east of the Andes during the SALLJEX.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PB3-33.

Douglas, M. W., J. F. Mejia, 2006: Flow around the Andean elbow from WRF simulations and P-3 aircraft measurements during SALLJEX.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PB3-32.

Douglas, M. W., J. M. Galvez, R. Orozco, J. F. Mejjia, 2006: Plausible effects of Paleolake Tauca on the altiplano circulations and rainfall from WRF model simulations.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PB3-34.

Douglas, M. W., J. Regalado, J. Murillo, 2006: Atmospheric soundings across an oceanic front between the Galapagos Islands and the coast of South America from the INOCAR cruise of October 2005.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PA3-33. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Special radiosonde observations were made from the INOCAR research vessel Orion during the
second INOCAR oceanographic cruise of 2005. These observations were carried out for both
operational and scientific objectives. Operationally, we sought to evaluate the feasibility of
routinely making radiosonde observations from the ship, and determining what the ship might
need for such observations. Since relatively few upper air observations have been made
between the Galapagos Islands and the coast of Ecuador we wanted to obtain high spatial
resolution soundings across the equatorial cold tongue, which has been the subject of recent
research measurements farther west in the eastern Pacific. Some results of the boundary layer
over the cold tongue, based on the radiosonde measurements, are reported here. With some
modifications, the Orion is a suitable platform for routine atmospheric measurements in this
poorly sampled region of the eastern Pacific.

Douglas, M. W., L. Florez, N. Ordinola, J. Murillo, 2006: Variability of the meridional flow near the Equator from 8 years of pilot balloon observations at Piura, Peru.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PD3-14. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, Brazil, 73072.]

Pilot balloon observations have been made at Piura, Peru since 1997 as part of the PACS–SONET project. This data set is the most complete set of observations from SONET, andillustrates the value of a single station’s multi-year record for studies of interannual variability ofthe windfield near the equator.

Douglas, M. W., R. Orozco, J. M. Galvez, J. Murillo, J. F. Mejia, 2006: The seasonal evolution of the diurnal variation of the low-level winds around the Gulf of California. Is there a link to vegetation green-up during the wet season?. Preprints, 86th American Meteorological Annual Meeting (18th Conference on Climate Variability and Change), Atlanta, GA, Atlanta, GA, USA, American Meteorological Society, J3.4. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Sea-land breeze circulations are ubiquitous along the Gulf of California. Sea breezes are well developed because of the strong heating over the desertic regions along both sides of the Gulf. However, the sea surface temperature has a large seasonal range, especially over the northern Gulf. In addition, after the start of the summer rains there is a rapid foliation of the seasonal dry forest found along the eastern side of the Gulf. It was hypothesized that the rapid vegetation change and associated change in the land surface characteristics (albedo and evapotranspiration) might modify the sea-land breeze circulations. This might in turn affect the diurnal evolution of rainfall over the region. The recently ended North American Monsoon Experiment (NAME) afforded an opportunity to determine the possible seasonal variation of the sea-breeze intensity and its relationship with the onset of the rainy season. This presentation will describe the effort to measure the diurnal cycle of the winds and its seasonal variation. A network of 7 pilot balloon stations made observations twice-daily for approximately four months, with two of these making more frequent observations during special periods. Surface observations from automated surface stations were also available. The monthly mean winds from the different stations will be shown, as well as divergence estimates over different subregions of the pilot balloon array. The changes in sea-breeze intensity and the area-averaged divergence estimates will be compared with the seasonal evolution of the Gulf surface temperature and mean land surface temperature changes and the observed rainfall onset over the region.

Douglas, M. W., R. Orozco, J. M. Galvez, 2006: Diurnal variability of the cloud field over the VOCALS domain from GOES imagery.. Preprints, 86th American Meteorological Annual Meeting (14th Conference on Interaction of the Sea and Atmosphere), Atlanta, GA, USA, American Meteorological Society, P1.3. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

As part of ongoing studies of mesoscale variability over the South American altiplano we have produced averages of the cloudiness using GOES imagery. These composites are made at full resolution of the imagery, to help identify the relationship between the underlying topography and the cloud field. The upcoming VOCALS activity, focused on the stratocumulus region of the southeastern Pacific, has as one objective the description of the diurnal cycle of this cloudiness and its relationship to the South American continent. With this in mind, we have produced GOES imagery composites for the SE Pacific with 30 min temporal resolution. These composites show the diurnal variation of the cloudiness and its apparent propagation offshore. The composites are stratified by time of year. Comparison is made with the simulated diurnal cycles reported in the literature.

Douglas, M. W., T. Killeen, J. F. Mejia, 2006: Use of MODIS and GOES imagery to help delineate the distribution of cloud forests along the eastern Andean slopes.. Preprints, (14th Conference on Satellite Meteorology and Oceanography), Atlanta, GA, USA, American Meteorological Society, P3.18. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

The environment with the greatest biodiversity from a global standpoint is that known as the tropical Andes “hotspot”, which is a broad region along the eastern slopes of the Andes in South America. One of the subregions with the highest diversity within this region is the cloud forest, a region of very high cloudiness and high annual precipitation. Mapping the cloud forest and surrounding environments has been of high priority because resources for conservation are limited and conservation organizations and governmental agencies need to know what areas should receive highest priority for protection efforts.

Work associated with the South American Low-level Jet Experiment (SALLJEX) carried out in 2002-3 led to the use of GOES imagery to develop composites of visible and IR imagery for describing the mean cloudiness along the eastern slopes of the Andes. More recently MODIS imagery has been used to describe cloudiness at even higher resolution. Together, these imagery sources provide clues as to the distribution of cloudiness that can be related to cloud forest environment. In addition, dry canyon environments, the locus of many geographically-restricted species, can likewise be readily described from the cloudiness composites.

The GOES and MODIS cloudiness composites will be shown, and some limitations of inferring cloud forest locations and dry canyon habitat from the imagery will be discussed. The potential for this technique to be applied to other areas will be mentioned.

Douglas, M. W., N. Ordinola, J. F. Mejia, 2005: Rainfall variations along the coast of Peru and Ecuador during the 1997–8 El Niño and implications for a real-time forecasting system over the region. Preprints, Ninth Symposium on Integrated Observing and Assimilation Systems for the Atmosphere, Oceans, and Land Surface (IOAS-AOLS), 85th AMS Annual Meeting, San Diego, CA, USA, American Meterological Society, 5.2. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Special observations collected during the 1997-8 El Niño event along the coast of Peru and Ecuador have been re-evaluated, together with NCEP reanalyses and satellite imagery for the period. We had previously composited the special pilot balloon observations with respect to rainfall measurements made over the region to describe the wet- and dry-day characteristics. Recently, we have generated composites of satellite imagery and meteorological fields derived from the NCEP reanalyses and we have revised the composites done previously. We will show the mean fields associated with wet and dry days, together with the evolution of these fields. Satellite composites for the different periods will also be shown. Using these results we discuss the implications for a weather forecasting network over the region that experiences little rainfall, but when it occurs it is very important. The kinds of observations that might be needed for such a network, which might be temporary rather than permanent, are outlined. .

Douglas, M. W., J. Murillo, 2005: Reasons for the failure of the Pan American Climate Studies Sounding Network (PACS-SONET) in Latin America.. Preprints, Ninth Symposium on Integrated Observing and Assimilation Systems for the Atmosphere, Oceans, and Land Surface (IOAS-AOLS), San Diego, CA, USA, American Meteorological Society, p1.18. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

NOAA's Office of Global Programs has supported a network of pilot balloon stations in Latin America to provide wind measurements in areas where few observations previously existed. This network has existed since 1997 in various forms, with up to 20 sites providing daily or twice-daily observations. Although some success has been obtained, the network has not succeeded in obtaining self-sustainability within the host countries. This presentation will discuss some of the factors that have prevented a sustainable climate monitoring upper air network from being achieved. Many logistical factors have complicated the network's operation, but we feel that the main problem lies within the educational arena of the countries involved. The lack of meteorologically-educated personnel throughout the weather services and other institutions of the region has prevented and thorough understanding of the objectives of the network. In addition, the emphasis on inexpensive technology may have also generated the perception that the activity was not important because of the low overall cost. Some of these perception problems will be discussed in this presentation . A strategy for maintaining a self-sustaining activity will be outlined, though its feasibility may be in doubt.

Douglas, M. W., J. Murillo, J. F. Mejia, 2005: Conducting short duration field programs to evaluate sounding site representativness and potential climate monitoring biases-Examining the Low-Level Jet Over the Venezuelan Llanos During the 2005 Dry Season. Preprints, 13th Symposium on Meteorological Observations and Instrumentation, Savannah, GA, USA, American Meteorological Society, JP1.32.

Douglas, M. W., R. Orozco, J. M. Galvez, 2005: Measuring and monitoring the mesoclimate of tropical locations. Field observations from the South American altiplano during the SALLJEX. Preprints, 13th Symposium on Meteorological Observations and Instrumentation, Savannah, GA, USA, American Meteorological Society, 6.2.

Douglas, M. W., 2008: The Pan American Climate Studies Sounding Network. Bulletin of the American Meteorological Society, 89, 1709-1725.

A research effort primarily involving pilot balloon observations was carried out during the summer of 1997 to study rainfall variability over Central America. This activity, supported by NOAA's Pan American Climate Studies (PACS) program, grew in scope in response to the strong El Niño event of 1997/98 and subsequently evolved into a network ranging from Mexico to Paraguay. The overall goal of the PACS-Sounding Network (PACS-SONET) was to obtain relatively inexpensive wind profiles for describing climate variability over parts of the intertropical Americas that were not well covered by routine radiosonde observations. Major portions of the project supported climate research programs focusing on both the South and North American monsoon systems, while other parts of the network provided multiyear observations across important gaps in the Central American cordillera and also helped to describe cross-equatorial flow variations in the eastern Pacific. Approximately 50,000 observations were made by the PACS-SONET over its 10-yr operation.

This paper describes the motivation for and evolution of the network, the logistical complications that were involved in establishing and operating a long-term multinational network, and some of the important results from analysis of the data. We conclude by discussing some of our perspectives on why the network was unable to make a transition from research funding to one supported by meteorological services of the region.

Douglas, M. W., J. Mejia, R. Orozco, J. Murillo, 2008: Suggestions for upgrading the pilot balloon network in West Africa and elsewhere in the tropics. Extended Abstracts, TECO-2008 - WMO Technical Conference on Meteorological and Environmental Instruments and Methods of Observation, St. Petersburg, Russian Federation, World Meteorological Organization, 1(9).

Based on experience during the 2006 NAMMA field program we provide some recommendations for improving the pilot balloon network over the West Africa region. These range from relatively straightforward suggestions as to adjusting the launch time to maximize sounding height, to improved efforts to maintain the equipment and train observers. The supply of gas for balloon inflation is probably the largest logistical problem, followed by quality control of the data. The paper concludes by suggesting that the fastest way to upgrade the sounding network over Africa is to make it independent of National Meteorological Services and place it under an independent body that would oversee all aspects of its operation – for the benefit of Numerical Weather Prediction and climate monitoring objectives. The reasons for this seemingly drastic action are presented.

Available online at http://www.knmi.nl/samenw/geoss/wmo/TECO2008/IOM-96-TECO2008/1(09)_Douglas_USA.pdf.

Douglas, M. W., 2008: Progress towards development of the glidersonde: a recoverable radiosonde system. Extended Abstracts, TECO-2008 - WMO Technical Conference on Meteorological and Environmental Instruments and Methods of Observation, St. Petersburg, Russian Federation, World Meteorological Organization, P1(6).

The motivation and history of development of a recoverable radiosonde system using a glider lifted aloft by a radiosonde balloon – the “glidersonde”, is summarized in this poster. The current status of development efforts currently involve at least three separate groups; in the USA, in South Africa, and a version, developed in New Zealand, is now being marketed commercially. These efforts are briefly summarized, as are some limitations that still need to be overcome for widespread adoption of such technology.

Available online at http://www.knmi.nl/samenw/geoss/wmo/TECO2008/IOM-96-TECO2008/P1(06)_Douglas_USA.pdf.

Douglas, M. W., J. Mejia, N. Ordinola, J. Boustead, 2009: Synoptic Variability of Rainfall and Cloudiness along the Coasts of Northern Peru and Ecuador during the 1997/98 El Niño Event. Monthly Weather Review, 137, 116-136.

This paper describes the meteorological conditions associated with large fluctuations in rainfall over the coastal regions of northern Peru and Ecuador during the 1997/98 El Niño event. Using data from a network of routine rain gauges and special gauges established just prior to the onset of heavy rains, it is shown that large variations in the daily rainfall on quasi-weekly time scales occurred during the period January–April 1998. These rainfall fluctuations were approximately in phase along the coast from near the equator to ∼7°S. The daily rainfall data was averaged to develop a subset of wet and dry days, and then these dates were used as the basis for compositing. Special pilot balloon observations were composited with respect to the wet and dry days, showing that westerly and northerly wind anomalies are associated with wet spells. Composites of the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis and outgoing longwave radiation (OLR) data support a modest association of anomalous westerly wind events with enhanced rainfall.

The relationship observed between westerly zonal wind anomalies and rainfall west of the Andes during 1998 suggested using the NCEP reanalysis to develop composites based on westerly wind events observed during other years. Zonal wind anomalies at 700 hPa were used as the primary criterion for stratifying “wet” and “dry” days, despite reservations about the association between rainfall and zonal wind. Compositing Geostationary Operational Environmental Satellite (GOES) and OLR data for 220 west wind anomaly events from the months of January–April for the years 1990–2005 showed that they are associated with enhanced cloudiness that propagates eastward at ∼10 m s−1. The composites using NCEP reanalyses show the evolution of the wind field associated with the wet days and suggest a link between extratropical wave passages across North America and anomalous westerly wind events off the coast of Ecuador and northern Peru.

Douglas, M. W., 2010: Adaptive sounding arrays for tropical regions. Extended Abstracts, 29th Conference on Hurricanes and Tropical Meteorology, Tucson, AZ, USA, American Meteorological Society, 12B.7.

The advent of low initial-cost radiosonde systems (relative to previous systems available on the market) permits the establishment of radiosonde networks that can be operated "on-demand". This talk will describe the essential requirements to affordably operate such sounding networks, with particular application to the region important for hurricanes affecting the US. Key to the effectiveness of such adaptive networks are 1) low initial cost of the sounding system which permits many sites to be established, 2) relatively infrequent need for observations, 3) availability of personnel that are paid by observation rather than full-time staff, and 4) suitable locations that exist for additional sounding sites to be established. Two-way communications with the stations is critical, since the observations would be intermittent. The greatest challenge is likely to be in deciding when to make observations – which observations are likely to have the greatest impact on forecast skill and over what time frame? A comparison will be made between the current hurricane season “enhanced” sounding network in the Caribbean Sea region and what might be possible for the same budget via an adaptive strategy.

Available online at http://ams.confex.com/ams/29Hurricanes/techprogram/MEETING.HTM.

Douglas, M. W., J. F. Mejia, 2010: Testing a low-cost radiosonde system for possible use in adaptive sounding networks. Extended Abstracts, 15th Symposium on Meteorological Observation and Instrumentation, Atlanta, GA, USA, American Meteorological Society, P265.

Recently the National Severe Storms Laboratory obtained a low-cost (~$10K) Intermet 3050 radiosonde system for testing as a possible supplement to existing laboratory systems. The purpose of this testing has been to evaluate the quality of the data from the Intermet radiosondes by compariong these data with data from other radiosondes. Also, we are evaluating the signal strength from the Internet's omni-directional antenna, the system's portability, and different aspects of the software. To date, testing has involved same-balloon ascent comparisons between both NSSL's Vaisala RS-92 radiosondes and National Weather Service Sippican Mark 2 radiosondes. This presentation will describe the procedures used to carry out the comparisons between the different radiosonde sensors and the results. Every one of the nine same-balloon train launches at the Albuquerque NWS radiosonde site in July-August 2009 showed a systematic offset between the humidity values from the Sippican and Intermet sondes, with the Sippican sondes showing lower relative humidities of 5-10% in the lower- through mid- troposphere. However, the differences varied with height. Fewer comparisons have been made between the Vaisala and Intermet sondes to date, but results from this comparison are expected well prior to the AMS Meeting.

Available online at http://ams.confex.com/ams/90annual/techprogram/programexpanded_575.htm.

Douglas, M. W., J. F. Mejia, D. B. Enfield, 2010: Developing an enhanced climate monitoring network for the Inter-American seas region. Extended Abstracts, 14th Symposium on Integrated Observing and Assimilation Systems for the Atmosphere, Oceans, and Land Surface (IOAS-AOLS), Atlanta, GA, USA, American Meteorological Society, 6A.6.

The Intra-Americas Study of Climate Processes (IASCLIP) is a research program that has objectives of improving climate prediction over and bordering the Inter-American Seas region, a region roughly extending from the Gulf of Mexico to northern South America. This region has not been the focus of previous US CLIVAR-supported research activities such as NAME, MESA, and most recently VOCALS.
The IASCLIP domain, although being somewhat well-covered by routine meteorological measurements because of the operational interest in hurricane forecasting, presents complications for developing a climate monitoring network suitable for addressing many research questions. The presence of large islands and complicate land-sea boundaries produces large amplitude and complex local circulations modified by the diurnal cycle of solar heating. Most routine observation sites (either surface or upper-air) are affected by these local influences, leading to uncertainties in the mean over-ocean conditions.
This presentation provides an overview of some measurement needs, logistical complications, and potential observation strategies being considered for both oceanic and atmospheric measurements that will be required for advancing climate research activities in the region.

Available online at http://ams.confex.com/ams/90annual/techprogram/programexpanded_576.htm.

Douglas, M. W., J. F. Mejia, 2010: The recent availability of low-cost radiosonde systems and their implications for adaptive sounding arrays. Extended Abstracts, 15th Symposium on Meteorological Observation and Instrumentation, Atlanta, GA, USA, American Meteorological Society, 9.5.

Available online at http://ams.confex.com/ams/90annual/techprogram/programexpanded_575.htm.

Douglas, M. W., J. F. Mejia, 2010: Evaluating a new low-cost radiosonde system for use in adaptive sounding networks. Extended Abstracts, Lubbock Severe Weather Workshop, Lubbock, TX, USA, National Weather Service, Texas Tech University, ppt file.

Available online at http://lubsvrconf.org/pres_links.php.

Douglas, M. W., J. F. Mejia, 2009: Requirements for developing an adaptive radiosonde network for improved regional weather forecasting over southwestern North America. Extended Abstracts, Fifth Symposium on Southwest Hydrometeorology, Albuquerque, NM, USA, National Weather Service, University of New Mexico, ppt file.

Available online at http://www.srh.noaa.gov/abq/?n=sswhm2009abq.

Elmore, K. L., H. D. Reeves, T. M. Smith, K. L. Ortega, 2011: A winter hydrometeor classification algorithm. Preprints, 9th Conference on Artificial Intelligence, Seattle, WA, USA, American Meteorological Society, J6.1.

Over the past two winter seasons, the National Severe Storms Laboratory (NSSL) has collected observations of precipitation type from anonymous, volunteer public observers though the Winter Precipitation Identification Near the Ground (W-PING) project. To date, nearly 3,000 observations of winter precipitation type have been logged through a web based form hosted by the NSSL. Analysis of these reports shows that the current hydrometeor classification algorithm (HCA), which was developed with warm season convection in mind, performs poorly when confronted with winter precipitation. This project proposes to use these data, along with new capabilities within the warning decision support system integrated information (WDSSII) system, to build a data driven winter surface precipitation classifier and implement it within WDSSII.
The WDSSII system has the ability to extract vertical profiles of environmental data from rapid update cycle (RUC) model grids at designated times and locations. In addition, these profiles may be tilted at angles from the vertical to take into account the fact that precipitation source and generating regions are upwind from the surface observation location. Environmental data is on a rectilinear grid, but WDSSII can now interpolate the rectilinear data onto the spherical grid used by radar data. Hence, the radar range gates and the environmental data can be colocated.

With these capabilities it is possible to construct a complete set of radar and model based environmental attributes associated with any given observation within the W-PING data base. With these capabilities also comes the ability to build a hybrid winter surface precipitation classifier using a mixture of rule-based and data driven, statistically principled methods. The algorithm will generate classifications for surface precipitation type only; it will not create classifications for precipitation aloft because there are no verification data aloft.

The resulting classifier is evaluated statistically through various performance scores such as POD, FAR and CSI along with various other skill scores, such as the Heidke and Peirce skill scores. As envisioned, the classifier will define at least four basic categories: liquid, freezing, frozen and none. The frozen category may be divided into two subcategories: “snow” and “not snow,” depending upon the quality and quantity of appropriate W-PING data.

Available online at http://ams.confex.com/ams/91Annual/webprogram/Paper185800.html.

Engerer, N. A., D. J. Stensrud, M. C. Coniglio, 2008: Surface Characteristics of Observed Cold Pools. Monthly Weather Review, 136, 4839-4849.

Cold pools are a key element in the organization of precipitating convective systems, yet knowledge of their typical surface characteristics is largely anecdotal. To help alleviate this situation, cold pools from 39 mesoscale convective system (MCS) events are sampled using Oklahoma Mesonet surface observations. One thousand three hundred and eighty-nine time series of surface observations are used to determine typical rises in surface pressure and decreases in temperature, potential temperature, and equivalent potential temperature associated with the cold pool, and the maximum wind speeds in the cold pool. The data are separated into one of four convective system lifecycle stages: first storms, MCS initiation, mature MCS, and MCS dissipation. Results indicate that the mean surface pressure rises associated with cold pools increase from 3.2 hPa for the first storms lifecycle stage to 4.5 hPa for the mature MCS stage before dropping to 3.3 hPa for the dissipation stage. In contrast, the mean temperature (potential temperature) deficits associated with cold pools decrease from 9.5 K (9.8 K) to 5.4 K (5.6 K) from the first storms to dissipation stage, with a decrease of approximately 1 K associated with each advance in lifecycle stage. However, the daytime and early evening observations show mean temperature deficits over 11 K. A comparison of these observed cold pool characteristics with results from idealized numerical simulations of MCSs suggests that observed cold pools likely are stronger than those found in model simulations, particularly when ice processes are neglected in the microphysics parameterization. The mean deficits in equivalent potential temperature also decrease with MCS lifecycle stage, starting at 21.6 K for first storms and dropping to 13.9 K for dissipation. Mean wind gusts are above 15 m s-1 for all lifecycle stages. These results should help numerical modelers determine if the cold pools in high-resolution models are in reasonable agreement with the observed characteristics found herein. Thunderstorm simulations and forecasts with thin model layers near the surface also are needed to obtain better representations of cold pool surface characteristics that can be compared with observations.

Fast, J. D., R. K. Newsom, K. J. Allwine, Q. Xu, P. Zhang, J. H. Copeland, J. Sun, 2007: Using NEXRAD wind retrievals as input to atmospheric dispersion models. Extended Abstracts, Seventh Symposium on the Urban Environment, San Diego, CA, USA, Amer. Meteor. Soc., 8.2.

Available online at http://ams.confex.com/ams/7Coastal7Urban/techprogram/paper_127244.htm.

Fast, J. D., R. K. Newsom, K. J. Allwine, Q. Xu, P. Zhang, J. Copeland, J. Sun, 2008: An evaluation of two NEXRAD wind retrieval methedologies and their use in atmospheric dispersion models. Journal of Applied Meteorology and Climatology, 47, 2351-2371.

Feltz, W. F., K. Bah, K. Bedka, J. Gerth, J. S. Kain, S. Lindstrom, J. Otkin, T. Schmidt, J. Sieglaff, C. Siewert, R. Rabin, 2010: UW-CIMSS GOES-R Proving Ground Participation in Storm Prediction Center Hazardous Weather Testbed. Preprints, 17th Conference on Satellite Meteorology and Oceanography, Annapolis, MD, USA, Amer. Meteor. Soc.,, P9.9.

Fierro, A. O., L. Leslie, E. Mansell, J. Straka, D. MacGorman, C. Ziegler, 2007: A High-resolution Simulation of Microphysics and Electrification in an Idealized Hurricane-like Vortex. Meteorology and Atmospheric Physics, 98, 13-33.

Cloud-to-ground (CG) lightning bursts in the eyewall of mature tropical cyclones (TCs) are believed to be good indicators of imminent intensification of these systems. While numerous well-documented observational cases exist in the literature, no modeling studies of the electrification processes within TCs have previously been conducted. At present, little is known about the evolution of charge regions and lightning activity in mature TCs. Towards this goal, a numerical cloud model featuring a 12-class bulk microphysics scheme with electrification and lightning processes is utilized to investigate the evolution of the microphysics fields and subsequent electrical activity in an idealized hurricane-like vortex.

Preliminary results show that the highest total lightning flash rates (CG plus intracloud) are primarily found within the eyewall where updraft speeds tend to be larger than elsewhere in the TC, though rarely exceeding 10 m s^-1. Smaller total flash rates are also found within the strongest cells forming the outer bands, where updraft speeds sometimes reach 15 m s^-1. As expected, these two regions of the storm are generally characterized by moderate total graupel mixing ratio (> 0.5 g kg^-1) and moderate cloud water content (> 0.2 g m^-3). When the model uses the Saunders and Peck non-inductive (NI) charging scheme and moderate inductive charging settings, the inner eyewall region exhibits a complex charge structure. However, the charge regions involved in lightning can be described as a normal tripole charge structure in the eyewall, while a normal dipole is observed in the outer eyewall stratiform region and in the strongest cells forming the outer rainbands. The charges forming the normal dipole in the outer eyewall are generated within the eyewall via NI charging in the mixed-phase region at mid-levels (near the -10 deg C isotherm) and later, are ejected radially outward by the storm’s intense circulation.

Fritz, A., V. Lakshmanan, T. M. Smith, E. Forren, B. Clarke, 2006: A validation of radar reflectivity control methods. Preprints, 22nd Conference on Interactive Information Processing Systems, Atlanta, GA, USA, AMS, CD-ROM, 9.10.

Available online at http://ams.confex.com/ams/Annual2006/techprogram/paper_102136.htm.

Fujita, T., D. J. Stensrud, D. C. Dowell, 2005: Surface data assimilation using an ensemble Kalman filter approach with initial condition and model physics uncertainties. Preprints, 11th Conf. on Mesoscale Processes, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, 1M.3.

Fujita, T., D. J. Stensrud, D. C. Dowell, 2007: Surface data assimilation using an ensemble Kalman filter approach with initial condition and model physics uncertainty. Monthly Weather Review, 135, 1846-1868.

The assimilation of surface observations using an ensemble Kalman filter (EnKF) approach is evaluated for the potential to improve short-range forecasting. Two severe weather cases are examined, in which the assimilation is performed over a 6-h period using hourly surface observations followed by an 18-h simulation period. Ensembles are created in three different ways, by using different initial and boundary conditions, by using different model physical process schemes, and by using both different initial and boundary conditions and different model physical process schemes. The ensembles are compared in order to investigate the role of uncertainties in the initial and boundary conditions and physical process schemes in EnKF data assimilation. In the initial condition ensemble, spread is associated largely with the displacement of atmospheric baroclinic systems. In the physics ensemble, spread comes from the differences in model physics, which results in larger spread in temperature and dewpoint temperature than the initial condition ensemble, and smaller spread in the wind fields. The combined initial condition and physics ensemble has properties from both of the previous two ensembles. It provides the largest spread and produces the best simulation for most of the variables, in terms of the rms difference between the ensemble mean and observations. Perhaps most importantly, this combined ensemble provides very good guidance on the mesoscale features important to the severe weather events of the day.

Fujita, T., D. J. Stensrud, D. C. Dowell, 2008: Using Precipitation Observations in a Mesoscale Short-Range Ensemble Analysis and Forecasting System. Weather and Forecasting, 23, 357-372.

A simple method to assimilate precipitation data from a synthesis of radar and gauge data is developed to operate alongside an ensemble Kalman filter that assimilates hourly surface observations. The mesoscale ensemble forecast system consists of 25 members with 30-km grid spacing and incorporates variability in both initial and boundary conditions and model physical process schemes. The precipitation assimilation method only incorporates information on when and where rainfall is observed. Model temperature and water vapor mixing ratio profiles at each grid point are modified if rainfall is observed but not predicted, or if rainfall is predicted but not observed. These modifications act to either increase or decrease, respectively, the likelihood that precipitation develops at that grid point.

Two cases are examined in which this technique is applied to assimilate precipitation data every 15 min from 1200 to 1800 UTC, while hourly surface observations are also assimilated at the same time using the more sophisticated ensemble Kalman filter approach. Results show that the simple method for assimilating precipitation data helps the model develop precipitation where it is observed, resulting in the precipitation area being reproduced more accurately than in the run without precipitation-data assimilation, while not negatively influencing the positive results from the surface data assimilation. Improvement is also seen in the reliability of precipitation probabilities for a 1 mm h−1 threshold after the assimilation period, indicating that assimilating precipitation data may provide improved forecasts of the mesoscale environment for a few hours.

Gao, J., M. Xue, S. Lee, A. Shapiro, Q. Xu, K. K. Droegemeier, 2006: A three-dimensional variational single-doppler velocity retrieval method with simple conservation equation constraint. Meteorol. Atmos. Phys., 94, 11-26.

Gao, J., D. J. Stensrud, T. M. Smith, K. Manross, J. Brogden, K. Kuhlman, 2011: A Realtime Weather-Adaptive 3DVAR Analysis System with Automatic Storm Positioning and On-demand Capability. Extended Abstracts, 35th Conference on Radar Meteorology, Denver, CO, USA, AMS, 115.

Radar is a fundamental tool for severe storm monitoring and nowcasting activities. Forecasters examine real-time NEXRAD observations from multiple radars, other remote sensing tools, severe weather detection algorithms, and use their considerable experience and situational awareness to issue severe storm warnings that help protect the public from hazardous weather events. However, escalating data flow rates from new sensors and applications will make it challenging for forecasters to make the best use of all the available data in warning operations in a timely manner. To overcome this difficulty, a real-time, weather-adaptive three-dimensional variational data assimilation (3DVAR) system has been developed recently for NOAA supported Warn-on-Forecast project (WoF) to incorporate all available traditional and radar observations within an analysis domain that could be hit by severe weather, including tornadoes, hails and strong damage winds. The unique features include: (1) The system has the ability to automatically detect and analyze severe local hazardous weather events at 1km horizontal resolution every 5 minutes. (2) The analysis can also be performed with on-demand capability in which end-users (or forecasters) set up the location of the analysis domain in real time based on the current weather situation. (3) The analysis product can help forecasters identify strong circulations imbedded in thunderstorms so that the accuracy of warnings for hazardous weather threats may be improved Although still in the early development stage, the system performed very well during the spring of 2010. Many severe weather events were all successfully detected and analyzed. Currently, we are working to make the analysis product available in "near realtime" (4-5 minutes delay) to the NWS forecasters as one of the official projects of the NOAA's HWT Experimental Warning Program. The objectivity of the procedure ensures that (i) all available information, including all nearby WSR-88Ds and NAM high resolution analysis and forecast products, are used, (ii) physically-consistent gridded data are provided to forecasters to help make their warning decisions in a timely manner, and (iii) the problem of subjectivity, inherent to some arbitrary criteria in some severe weather detection algorithms, is avoided. The performance of the system during the 2011 Spring season experiment will be reported during the conference.

Available online at http://ams.confex.com/ams/35Radar/webprogram/Paper191834.html.

Gao, J., D. J. Stensrud, 2012: Assimilation of Reflectivity Data in a Convective-Scale, Cycled 3DVAR Framework with Hydrometeor Classification. Journal of the Atmospheric Sciences, 69, 1054-1065.

The impact of assimilating radar reflectivity and radial velocity data with an intermittent, cycled threedimensional variational assimilation (3DVAR) system is explored using an idealized thunderstorm case and a real data case on 8 May 2003. A new forward operator for radar reflectivity is developed that uses a background temperature field provided by a numerical weather prediction model for automatic hydrometeor classification. Three types of experiments are performed on both the idealized and real data cases. The first experiment uses radial velocity data only, the second experiment uses both radial velocity and reflectivity data without hydrometeor classification, and the final experiment uses both radial velocity and reflectivity data with hydrometeor classification. All experiments advance the analysis state to the next observation time using a numerical model prediction, which is then used as the background for the next analysis. Results from both the idealized and real data cases show that, assimilating only radial velocity data, the model can reconstruct the supercell thunderstorm after several cycles, but the development of precipitation is delayed because of the well-known spinup problem. The spinup problem is reduced dramatically when assimilating reflectivity without hydrometeor classification. The analyses are further improved using the new reflectivity formulation with hydrometeor classification. This study represents a successful first effort in variational convective-scale data assimilation to partition hydrometeors using a background temperature field from a numerical weather prediction model.

Available online at http://journals.ametsoc.org/toc/atsc/69/3?ai=sf&ui=13y&af=H.

Gilleland, E., M. Pocernich, H. E. Brooks, 2006: Analyzing the Extreme Behavior of Large-Scale Meteorlogical Variables Found To Have Influence on Severe Storms and Tornadic Events Using Global Reanalysis Data. Extended Abstracts, 2006 Joint Statistical Meetings (JSM) of the American Statistical Association (ASA): Statistics for an uncertain world: Meeting global challenges, Seattle, WA, USA, American Statistical Association, 453-453.

Godfrey, C. M., D. J. Stensrud, L. M. Leslie, 2005: The influence of improved land surface and soil data on mesoscale model predictions. Proc. 19th Conference on Hydrology, San Diego, CA, USA, American Meteorological Society, CD-ROM, 4.7.

One of the most difficult aspects in the evaluation of land surface models is the lack of observational data for accurate specification of the model initial conditions. Routine observations of fractional vegetation coverage and leaf area index (LAI) are not available at high resolution (~1 km), nor are observations of soil moisture and soil temperature. This gap in our observational capabilities seriously hampers the evaluation and improvement of land surface model parameterizations, since model errors may be related to improper initial conditions as much as to inaccuracies in the model formulations. To overcome these difficulties, two unique data sets are used. First, fractional vegetation coverage and LAI are derived from biweekly maximum normalized difference vegetation index (NDVI) composites at 1 km resolution obtained from daily observations by the Advanced Very High Resolution Radiometer (AVHRR) onboard National Oceanic and Atmospheric Administration satellites. Second, the Oklahoma Mesonet measures soil moisture and soil temperature at 15-minute intervals. Combined, these two data sets provide significantly improved initial conditions for land surface models and allow us to evaluate the utility of the land surface models with much greater confidence and detail than previously.

The value of these two data sources to land surface model initializations is evaluated using the Penn State-NCAR fifth-generation Mesoscale Model (MM5). Forecasts that both include and neglect these unique land surface observations are compared. Results are verified against the dense network of surface observations afforded by the Oklahoma Mesonet, including surface flux data derived from special sensors available at some of the Mesonet sites. Implications for further data requirements are discussed.

Godfrey, C. M., D. J. Stensrud, L. M. Leslie, 2006: Soil temperature and moisture errors in Eta model analyses. Proc. 20th Conf. on Hydrology, Atlanta, GA, USA, Amer. Meteor. Soc., CD-ROM, JP1.2.

Forecast models require accurate soil temperature and soil moisture conditions to be able to properly partition the surface heat fluxes that drive the evolution of the planetary boundary layer. The National Centers for Environmental Prediction (NCEP) operational Eta model produces land surface analyses by continuously cycling soil temperature and moisture fields. In the past, these fields evolved only in response to radiation budget constraints and modeled precipitation, but NCEP recently upgraded the self-cycling process to assimilate observed precipitation. This study highlights potential problems with the land surface analysis from the Eta model by comparing 00 UTC and 12 UTC Eta model analyses of soil temperature and moisture at several depths with observations from the Oklahoma Mesonet. There are strong biases in soil temperature and there is a severe underestimation of soil moisture at all depths. There is notable improvement in the analyzed soil moisture fields after the change to a new assimilation scheme. While this change reduced the magnitude of the errors, a strong dry bias persists in the soil moisture field. A simple one-layer slab soil model reveals that these soil moisture errors alone may account for 1.0-1.5 degrees Celsius increases in maximum soil temperatures during the day and reductions in soil temperatures at night of 0.3-0.8 degrees Celsius. The remaining soil temperature errors likely stem from documented problems with the solar radiation and longwave parameterizations within the Eta model.

Available online at http://www.cimms.ou.edu/~cgodfrey/landsfc/.

Godfrey, C. M., D. J. Stensrud, 2008: Soil Temperature and Moisture Errors in Operational Eta Model Analyses. Journal of Hydrometeorology, 9, 367-387.

Proper partitioning of the surface heat fluxes that drive the evolution of the planetary boundary layer in numerical weather prediction models requires an accurate specification of the initial state of the land surface. The National Centers for Environmental Prediction (NCEP) operational Eta Model is used to produce land surface analyses by continuously cycling soil temperature and moisture fields. These fields previously evolved only in response to radiation budget constraints and modeled precipitation, but NCEP recently upgraded the self-cycling process so that soil fields respond instead to the radiation budget and observed precipitation. A comparison of 0000 and 1200 UTC Eta Model analyses of soil temperature and moisture at several soil depths with observations from the Oklahoma Mesonet during 2004 and 2005 shows that there are strong biases in soil temperature and a severe underestimation of soil moisture at all depths. After the change to a new assimilation scheme, there is notable improvement in the magnitude of the analyzed soil moisture fields, although a strong dry bias persists in the soil moisture field. A simple one-layer slab soil model quantifies the effect of such soil moisture errors on the diurnal cycle of soil temperature and reveals that these soil moisture errors alone may account for only 1.6°C increases in predicted maximum soil temperatures during the day and temperature reductions of the same magnitude at night. The much larger remaining soil temperature errors possibly stem from documented problems with the solar radiation and longwave parameterizations within the Eta Model.

Godfrey, C. M., D. J. Stensrud, 2010: An Empirical Latent Heat Flux Parameterization for the Noah Land Surface Model. Journal of Applied Meteorology and Climatology, 49, 1696-1713.

Proper partitioning of the surface energy fluxes that drive the evolution of the planetary boundary layer in numerical weather prediction models requires an accurate representation of initial land surface conditions. Unfortunately, soil temperature and moisture observations are unavailable in most areas and routine daily estimates of vegetation coverage and biomass are not easily available. This gap in observational capabilities seriously hampers the evaluation and improvement of land surface parameterizations, since model errors likely relate to improper initial conditions as much as to inaccuracies in the parameterizations. Two unique datasets help to overcome these difficulties. First, 1-km fractional vegetation coverage and leaf area index values can be derived from biweekly maximum normalized difference vegetation index composites obtained from daily observations by the Advanced Very High Resolution Radiometer onboard NOAA satellites. Second, the Oklahoma Mesonet supplies multiple soil temperature and moisture measurements at various soil depths each hour. Combined, these two datasets provide significantly improved initial conditions for a land surface model and allow an evaluation of the accuracy of the land surface model with much greater confidence than previously. Forecasts that both include and neglect these unique land surface observations are used to evaluate the value of these two data sources to land surface initializations. The dense network of surface observations afforded by the Oklahoma Mesonet, including surface flux data derived from special sensors, provides verification of the model results, which indicate that predicted latent heat fluxes still differ from observations by as much as 150 W m-2. This result provides a springboard for assessing parameterization errors within the model. A new empirical parameterization developed using principal-component regression reveals simple relationships between latent heat flux and other surface observations. Periods of very dry conditions observed across Oklahoma are used advantageously to derive a parameterization for evaporation from bare soil. Combining this parameterization with an empirical canopy transpiration scheme yields improved sensible and latent heat flux forecasts and better partitioning of the surface energy budget. Surface temperature and mixing ratio forecasts show improvement when compared with observations.

Gourley, J. J., Z. L. Flamig, Y. Hong, T. J. Schuur, S. Giangrande, J. A. Vrugt, 2009: Hydrologic Performance of Rainfall Estimates from Polarimetric Radar. Proc. 34th Conference on Radar Meteorology, Williamsburg, VA, USA, American Meteorological Society, P14.18.

Gourley, J. J., D. P. Jorgensen, S. Y. Matrosov, Z. L. Flamig, 2009: Evaluation of incremental improvements to quantitative precipitation estimates in complex terrain. J. Hydrometeor., 10, 1507-1520.

Gourley, J. J., Y. Hong, Z. L. Flamig, L. Li, J. Wang, 2010: Intercomparison of rainfall estimates from radar, satellite, gauge, and combinations for a season of record rainfall. Journal of Applied Meteorology and Climatology, 49, 437-452.

Gourley, J. J., S. E. Giangrande, Y. Hong, Z. L. Flamig, T. J. Schuur, J. A. Vrugt, 2010: Impacts of polarimetric radar observations on hydrologic simulation. J. Hydrometeor., 11, 781-796.

Gourley, J. J., Y. Hong, Z. L. Flamig, J. Wang, H. Vergara, E. N. Anagnostou, 2011: Hydrologic Evaluation of Rainfall Estimates from Radar, Satellite, Gauge, and Combinations on Ft. Cobb Basin, Oklahoma. Journal of Hydrometeorology, 12, 973-988.

This study evaluates rainfall estimates from the Next Generation Weather Radar (NEXRAD), operational rain gauges, Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA), and Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks Cloud Classification System (PERSIANN-CCS) in the context as inputs to a calibrated, distributed hydrologic model. A high-density Micronet of rain gauges on the 342-km2 Ft. Cobb basin in Oklahoma was used as reference rainfall to calibrate the National Weather Service’s (NWS) Hydrology Laboratory Research Distributed Hydrologic Model (HL-RDHM) at 4-km/l-h and 0.25°/3-h resolutions. The unadjusted radar product was the overall worst product, while the stage IV radar product with hourly rain gauge adjustment had the best hydrologic skill with a Micronet relative efficiency score of −0.5, only slightly worse than the reference simulation forced by Micronet rainfall. Simulations from TRMM-3B42RT were better than PERSIANN-CCS-RT (a real-time version of PERSIANN-CSS) and equivalent to those from the operational rain gauge network. The high degree of hydrologic skill with TRMM-3B42RT forcing was only achievable when the model was calibrated at TRMM’s 0.25°/3-h resolution, thus highlighting the importance of considering rainfall product resolution during model calibration.

Grunwald, S., H. E. Brooks, 2011: Relationship between sounding derived parameters and the strength of tornadoes in Europe and the USA from reanalysis data. Atmospheric Research, 100, 479-488.

Proximity soundings from reanalysis data for tornado events in Europe for the years 1958 to 1999 and in the US for the years 1991 to 1999 have been used for generating distributions of parameter combinations important for severe convection. They include parcel updraft velocity (WMAX) and deep-layer shear (DLS), lifting condensation level (LCL) and deep-layer shear (DLS), and LCL and shallow-layer shear (LLS) for weak and significant tornadoes. We investigate how well they discriminate between weak and significant tornadoes. For Europe, these distributions have been generated for unrated, F0 and F1 tornadoes as well to discover if the unrated tornadoes can be associated with the weak tornadoes.
The pattern of parameter combination distributions for unrated tornadoes in Europe strongly resembles the pattern of F0 tornadoes. Thus, the unrated tornadoes are likely to consist of mostly F0 tornadoes. Consequently, the unrated tornadoes have been included into the weak tornadoes and distributions of parameter combinations have been generated for these.
In Europe, none of the three combinations can discriminate well between weak and significant tornadoes, but all can discriminate if the unrated tornadoes are included with the weak tornadoes (unrated/weak). In the US, the combinations of LCL and either of the shear parameters discriminate well between weak and significant tornadoes, with significant tornadoes occurring at lower LCL and higher shear values than the weak ones. In Europe, the shear shows the same behavior, but the LCL behaves differently, with significant tornadoes occurring at higher LCL than the unrated/weak ones. The combination of WMAX and DLS is a good discriminator between unrated/weak and significant tornadoes in Europe, but not in the US, with significant tornadoes occurring at a higher WMAX and DLS than the unrated/weak tornadoes.

Available online at http://www.nssl.noaa.gov/users/brooks/public_html/papers/grunwaldbrooks2011.pdf.

Gutowski, Jr., W. J., G. C. Hegerl, G. J. Holland, T. R. Knutson, L. O. Mearns, R. J. Stouffer, P. J. Webster, M. F. Wehner, F. W. Zwiers, H. E. Brooks, K. A. Emanuel, P. D. Komar, J. P. Kossin, K. E. Kunkel, R. McDonald, G. A. Meehl, R. J. Trapp, 2008: Causes of Observed Changes in Extremes and Projections of Future Changes. Weather and Climate Extremes in a Changing Climate Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands: Synthesis and Assessment Product 3.3 Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change, T. R. Karl, G. A. Meehl, C. D. Miller, S. J. Hassol, A. M. Waple, W. L. Murray, Ed(s)., U.S. Climate Change Science Program and the Subcommittee on Glob, 81-116.

Hamill, T. M., R. Schneider, H. E. Brooks, G. Forbes, H. B. Bluestein, M. Steinberg, D. Melendez, R. M. Dole, 2005: The May 2003 extended tornado outbreak. Bulletin of the American Meteorological Society, 86, 531-542.

In May 2003 there was a very destructive extended outbreak of tornadoes across the central and eastern United States. More than a dozen tornadoes struck each day from 3 May to 11 May 2003. This outbreak caused 41 fatalities, 642 injuries, and approximately $829 million dollars of property damage. The outbreak set a record for most tornadoes ever reported in a week (334 between 4-10 May), and strong tornadoes (F2 or greater) occurred in an unbroken sequence of nine straight days. Fortunately, despite this being one of the largest extended outbreaks of tornadoes on record, it did not cause as many fatalities as in the few comparable past outbreaks, due in large measure to the warning efforts of National Weather Service, television, and private-company forecasters and the smaller number of violent (F4-F5) tornadoes. This event was also relatively predictable; the onset of the outbreak was forecast skillfully many days in advance.

An unusually persistent upper-level trough in the intermountain west and sustained low-level southerly winds through the southern Great Plains produced the extended period of tornado-favorable conditions. Three other extended outbreaks in the past 88 years were statistically comparable to this outbreak, and two short-duration events (Palm Sunday 1965 and the 1974 Superoutbreak) were comparable in the overall number of strong tornadoes. An analysis of tornado statistics and environmental conditions indicates that extended outbreaks of this character occur roughly every 10 to 100 years.

Harasti, P. R., D. Smalley, M. Weber, C. Kessinger, Q. Xu, P. Zhang, S. Liu, T. Tsui, J. Cook, Q. Zhao, 2005: On the development of a multi-algorithm radar data quality control system at the naval research laboratory. 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, XXXX.

Heinselman, P., S. Weiss, M. Coniglio, D. Andra, G. Stumpf, B. Phillips, J. Brotzge, cited 2008: 2008 Spring HWT Experiments at the NWC. [Available online at ://http://www.nwas.org/newsletters/pdf/news_october2008.pdf.]

Heinselman, P. L., D. J. Stensrud, R. M. Hluchan, P. L. Spencer, P. C. Burke, K. L. Elmore, 2009: Radar reflectivity-based estimates of mixed-layer depth. Journal of Atmospheric and Oceanic Technology, 26, 229-239.

This study investigates the potential for estimating mixed-layer depth by taking advantage of the radial gradients in the radar reflectivity field produced by the large vertical gradients in water vapor mixing ratio that are characteristic of the mixing height. During the day, this relationship often results in a ring of maximum reflectivity observed to progress radially outward from the radar as mixed-layer depth increases. A comparison of mixed-layer depths estimated from the Oklahoma City WSR-88D (KTLX) with those estimated from a nearby 915 MHz profiler reveals that mixed-layer depths from the WSR-88D are slightly too high (up to 0.3 km) during the first three hours of the diurnal cycle, nearly unbiased midday, and slightly too low (0.2 km or less) thereafter. The procedure estimates mixed-layer depths only during the daytime hours from 1300–2300 UTC. The weather conditions for the 17 days studied were fairly quiescent, with sunny skies and light winds.

Higgins, W., D. Ahijevych, J. Amador, A. Barros, E. Berbery, E. Caetano, R. Carbone, P. Ciesielski, R. Cifelli, M. Cortez-Vazquez, A. Douglas, M. Douglas, G. Emmanuel, C. Fairall, D. Gochis, D. Gutzler, T. Jackson, R. Johnson, C. King, T. Lang, M. Lee, D. Lettenmaier, R. Lobato, V. Magaña, J. Meitin, K. Mo, S. Nesbitt, F. Ocampo-Torres, E. Pytlak, P. Rodgers, S. Rutledge, J. Schemm, S. Schubert, A. White, C. Williams, A. Wood, R. Zamora, C. Zhang, 2006: The NAME 2004 Field Campaign and Modeling Strategy. Bulletin of the American Meteorological Society, 87, 79-94.

Hoekstra, S., K. Klockow, R. Riley, J. Brotzge, H. Brooks, 2011: A Preliminary Look at the Social Perspective of Warn-on-Forecast: Preferred Tornado Warning Lead Time and the General Public's Perceptions of Weather Risks. Weather, Climate, and Society, 3, 128-140.

Tornado warnings are currently issued an average of 13 minutes in advance of a tornado (Golden and Adams 2000) and are based on a warn-on-detection paradigm (Erickson and Brooks 2006). However, computer model improvements may allow for a new warning paradigm, warn-on- forecast, to be established in the future (Stensrud et al. 2009). This would mean that tornado warnings could be issued one to two hours in advance, prior to storm initiation. In anticipation of the technological innovation, this study inquires whether the “warn-on-forecast” paradigm for tornado warnings may be preferred by the public (i.e., individuals and single families). Our sample is drawn from visitors to the National Weather Center in Norman, Oklahoma. During the summer and fall of 2009, surveys were distributed to 320 participants to assess their understanding and perception of weather risks and preferred tornado warning lead-time.

Responses were analyzed according to several different parameters including age, region of residency, educational level, number of children, and prior tornado experience. A majority of the respondents answered many of the weather risk questions correctly. They seemed to be familiar with tornado seasons; however, they were unaware of the relative number of fatalities caused by tornadoes and several additional weather phenomena each year in the United States. The preferred lead-time was 34.3 minutes according to average survey responses. This suggests that while the general public may currently prefer a longer average lead-time than the present system offers, the preference does not extend to the one to two hour time-frame theoretically offered by the warn-on-forecast system. When asked what they would do if given a one-hour lead-time, respondents reported that taking shelter was a lesser priority than when given a 15-minute leadtime, and fleeing the area became a slightly more popular alternative. A majority of respondents also reported the situation would feel less life threatening if given a one-hour lead-time. These results suggest that how the public responds to longer lead times may be complex and situationally-dependent, and further study must be conducted to ascertain the users for whom the longer lead-times would carry the most value. These results form the basis of an informative stated-preference approach to predicting public response to long (> 1 hour) warning lead times, using public understanding of the risks posed by severe weather events to contextualize leadtime demand.

Homar, V., D. J. Stensrud, J. J. Levit, D. R. Bright, 2006: Value of Human-Generated Perturbations in Short-Range Ensemble Forecasts of Severe Weather. Weather and Forecasting, 21, 347-363.

During the spring of 2003, the Storm Prediction Center, in partnership with the National Severe Storms Laboratory, conducted an experiment to explore the value of having operational severe weather forecasters involved in the generation of a short-range ensemble forecasting system. The idea was to create a customized ensemble to provide guidance on the severe weather threat over the following 48 h. The forecaster was asked to highlight structures of interest in the control run and, using an adjoint model, a set of perturbations was obtained and used to generate a 32-member fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) ensemble. The performance of this experimental ensemble is objectively evaluated and compared with other available forecasts (both deterministic and ensemble) using real-time severe weather reports and precipitation in the central and eastern parts of the continental United States. The experimental ensemble outperforms the operational forecasts considered in the study for episodes with moderate-to-high probability of severe weather occurrence and those with moderate probability of heavy precipitation. On the other hand, the experimental ensemble forecasts of low-probability severe weather and low precipitation amounts have less skill than the operational models, arguably due to the lack of global dispersion in a system designed to target the spread over specific areas of concern for severe weather. Results from an additional test ensemble constructed by combining automatic and manually perturbed members show the best results for numerical forecasts of severe weather for all probability values. While the value of human contribution in the numerical forecast is demonstrated, further research is needed to determine how to better use the skill and experience of the forecaster in the construction of short-range ensembles.

Homar, V., D. J. Stensrud, 2008: Subjective versus objective sensitivity estimates: application to a North African cyclogenesis. Tellus, 60A, 1064-1078.

An observing system simulation experiment is used to test and compare objective and subjective estimates of sensitivity of a forecast aspect to the initial condition (IC) fields for a case of rapidly developing cyclogenesis over the Western Mediterranean during 19–22 December 1979. The ability of sensitivity estimation methods to provide helpful guidance about where an improvement in the IC can lead to the largest forecast error reduction is particularly important to ascertain in order to guide adaptive observation campaigns.

Synthetic soundings from a 15-km reference simulation are added to an initially poor 60-km control simulation over the sensitive areas as determined by the combination of the given sensitivity estimate and a simple analysis error estimate. The ability of each sensitivity estimation method to produce an improved simulation of the cyclone is assessed.

Results show that while the sensitivity estimates perform similarly, with no significant differences among them, the subjective method yields the best overall targeting guidance. In contrast, the adjoint estimate provides the least accurate targeting guidance for this particular case and analysis error estimate. This suggests that subjective sensitivity estimation methods are able to compete with or even improve upon the objective estimation method for this case of cyclogenesis over the Western Mediterranean.

James, K. A., D. J. Stensrud, N. Yussouf, 2009: Value of Real-Time Vegetation Fraction to Forecasts of Severe Convection in High-Resolution Models. Weather and Forecasting, 24, 187-210.

Near-real-time values of vegetation fraction are incorporated into a 2-km nested version of the Advanced Research Weather Research and Forecasting (ARW) model and compared to forecasts from a control run that uses climatological values of vegetation fraction for eight severe weather events during 2004. It is hypothesized that an improved partitioning of surface sensible and latent heat fluxes occurs when incorporating near-real-time values of the vegetation fraction into models, which may result in improved forecasts of the low-level environmental conditions that support convection and perhaps even lead to improved explicit convective forecasts. Five of the severe weather events occur in association with weak synoptic-scale forcing, while three of the events occur in association with moderate or strong synoptic-scale forcing.

Results show that using the near-real-time values of the vegetation fraction alters the values and structure of low-level temperature and dewpoint temperature fields compared to the forecasts using climatological
vegetation fractions. The environmental forecasts that result from using the real-time vegetation fraction are more thermodynamically supportive of convection, including stronger and deeper frontogenetic circulations, and statistically significant improvements of most unstable CAPE forecasts compared to the control run. However, despite the improved environmental forecasts, the explicit convective forecasts using real-time vegetation fractions show little to no improvement over the control forecasts. The convective forecasts are generally poor under weak synoptic-scale forcing and generally good under strong synoptic-scale forcing. These results suggest that operational forecasters can best use high-resolution forecasts to help diagnose environmental conditions within an ingredients-based forecasting approach.

Jensen, T., B. Brown, M. C. Coniglio, J. S. Kain, S. J. Weiss, L. Nance, 2010: Evaluation of experimental forecasts from the 2009 NOAA Hazardous Weather Testbed Spring Experiment using both traditional and spatial methods. Preprints, 20th Conference on Probability and Statistics in the Atmospheric Sciences, Atlanta, GA, USA, Amer. Meteor. Soc., 527.

Jones, T. A., D. Stensrud, 2012: EnKF Assimilation of Cloud Properties Retrieved From GOES. Extended Abstracts, 92nd American Meteorological Society Annual Meeting: Eighth Annual Symposium on Future Operational Environmental Satellite Systems, New Orleans, LA, USA, AMS, 309.

Assimilation of various forms of satellite data into numerical weather prediction models has led to a significant increase in forecast skill during the past 25 years. Only recently have these efforts begun to be transitioned to mesoscale and storm-scale forecasts and initial research has shown promising results. One particular challenge in storm-scale data assimilation is properly identifying the location and intensity of convective features and the characteristics of the surrounding enviromnent prior to initiating forecasts. To examine whether or not hi-resolution satellite data can provide value added information, this research assimilates GOES cloud properties such as cloud top pressure, temperature, and cloud fraction into a forecast simulation of a severe weather outbreak that occurred in Oklahoma on 10 May 2010. The hypothesis posed by this research is that satellite derived cloud properties can provide information on the atmospheric state above and surrounding thunderstorms that will enable an improved model analysis of their characteristics, leading to improved short term forecasts. Traditional atmospheric observations are assimilated into the WRF-ARW model using a 36 member EnKF assimilation technique over a continental U.S. domain at 15 km resolution. GOES cloud data are then assimilated using the same technique on a 3 km nested grid domain centered around this event. Mesoscale data assimilation begins at 1200 UTC and continues until 2100 UTC 10 May with hourly GOES cloud data assimilated within the nested grid from 1800 to 2100 UTC. The effects of the satellite data assimilation are assessed by comparing two identical model experiments, one with and one without the satellite data, using 0 – 3 hour forecasts of thermodynamic conditions and simulated reflectivity. Observations from the VORTEX-2 expermient as well as radar and satellite observations are used to verify model output within the storm-scale domain.

Available online at http://ams.confex.com/ams/92Annual/webprogram/Paper198794.html.

Kain, J. S., S. J. Weiss, J. J. Levit, M. E. Baldwin, D. R. Bright, 2006: Examination of convection-allowing configurations of the WRF model for the prediction of severe convective weather: The SPC/NSSL Spring Program 2004. Weather and Forecasting, 21, 167-181.

Convection-allowing configurations of the Weather Research and Forecast (WRF) model were evaluated during the 2004 Storm Prediction Center–National Severe Storms Laboratory Spring Program in a simulated severe weather forecasting environment. The utility of the WRF forecasts was assessed in two different ways. First, WRF output was used in the preparation of daily experimental human forecasts for severe weather. These forecasts were compared with corresponding predictions made without access to WRF data to provide a measure of the impact of the experimental data on the human decision-making process. Second, WRF output was compared directly with output from current operational forecast models. Results indicate that human forecasts showed a small, but measurable, improvement when forecasters had access to the high-resolution WRF output and, in the mean, the WRF output received higher ratings than the operational Eta Model on subjective performance measures related to convective initiation, evolution, and mode. The results suggest that convection-allowing models have the potential to provide a value-added benefit to the traditional guidance package used by severe weather forecasters.

Kain, J. S., S. J. Weiss, D. R. Bright, M. E. Baldwin, J. J. Levit, G. W. Carbin, C. S. Schwartz, M. L. Weisman, K. K. Droegemeier, D. B. Weber, K. W. Thomas, 2007: Some practical considerations for the first generation of operational convection-allowing NWP: How much resolution is enough?. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 3B.5.

Kain, J. S., S. J. Weiss, D. R. Bright, M. E. Baldwin, J. J. Levit, G. W. Carbin, C. S. Schwartz, M. L. Weisman, K. K. Droegemeier, D. B. Weber, K. W. Thomas, 2008: Some practical considerations regarding horizontal resolution in the first generation of operational convection-allowing NWP. Weather and Forecasting, 23, 931-952.

During the 2005 NOAA Hazardous Weather Testbed Spring Experiment two different highresolution
configurations of the WRF-ARW model were used to produce 30 h forecasts five days
a week for a total of 7 weeks. These configurations used the same physical parameterizations and
the same input dataset for initial and boundary conditions, differing primarily in their spatial resolution.
The first set of runs used 4 km horizontal grid spacing with 35 vertical levels while the
second used 2 km grid spacing and 51 vertical levels.
Output from these daily forecasts is analyzed to assess the numerical forecast sensitivity to
spatial resolution in the upper end of the convection-allowing range of grid-spacing. The analysis
is based on a combination of visual comparison, systematic subjective verification conducted during
the Spring Experiment, and objective metrics based largely on the mean diurnal cycle of simulated
reflectivity and precipitation fields. Additional insight is gained by examining the size
distributions of individual reflectivity and precipitation entities and by comparing forecasts of
mesoscyclone characteristics in the two sets of forecasts.
In general, the 2 km forecasts provide more detailed presentations of convective activity, but
there appears to be little, if any, forecast skill on the scales where the added details emerge. On
the scales where both model configurations show higher levels of skill - the scale of mesoscale
convective features - the forecasts appear to provide comparable utility for severe weather forecasters.
These results suggest that 4 km grid spacing is a good place to start for the first generation
of 1-2 day convection-permitting operational NWP.

Kain, J. S., S. J. Weiss, D. R. Bright, M. E. Baldwin, J. J. Levit, G. W. Carbin, C. S. Schwartz, M. L. Weisman, K. K. Droegemeier, 2007: Some practical considerations for the first generation of operational convection-allowing NWP: How much resolution is enough?. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 3B.5. [Available from John S. Kain, NSSL, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

During the 2005 NOAA Hazardous Weather Testbed Spring Experiment (formerly known as the SPC/NSSL Spring Program) two different high-resolution configurations of the WRF-ARW model were used to produce 30 h forecasts five days a week for a total of 7 weeks. These configurations used the same physical parameterizations and the same input dataset for initial and boundary conditions, differing primarily in their spatial resolution. The first set of runs used 4 km horizontal grid spacing with 35 vertical levels while the second used 2 km grid spacing and 51 vertical levels.

This setup provided an unprecedented opportunity to assess the sensitivity to spatial resolution in the upper end of the convection-allowing range of grid-spacing, during many different severe-weather events. Of particular interest was whether the ~ ten fold increase in computing expense required by the 2 km runs could be justified by added value in the higher resolution forecasts. In this study, we examine and compare these forecasts from several different perspectives. First, we provide a visual examination of simulated reflectivity fields from selected convective events, highlighting the differences that might be detected by an operational forecaster – differences between the two model runs and the ways that both differ from observed reflectivity fields. Next, we present the results of subjective assessments of forecast skill, based on daily ratings assigned by panels of experts during the Spring Experiment. Then, we move on to objective measures of skill. These measures are based on time-averaged behavior characteristics of the models rather than selected points in time and space. For example, we examine the mean diurnal trends of simulated reflectivity and accumulated precipitation fields, as compared with observations. We compare the size distributions of individual reflectivity and precipitation entities, or “storms”, and we look at measures of storm rotation. Further, we look at traditional verification statistics such as equitable-threat and bias scores.

In general, we find that meteorological fields from the two model configurations behave much more like each other than like observations. The 2 km forecasts provide more detailed structures and appear to provide more realistic depictions of supercell-like storm configurations, both of which are intriguing to severe weather forecasters, but neither configuration shows much skill in predicting these small-scale features. On the scales where they show higher levels of skill – the scale of mesoscale convective features – the forecasts are often quite similar. The implications of these results, i.e., the value added by doubling resolution in this context, will be discussed at the conference.

Available online at http://ams.confex.com/ams/pdfpapers/124513.pdf.

Kain, J. S., S. J. Weiss, S. R. Dembek, J. J. Levit, D. R. Bright, J. L. Case, M. C. Coniglio, A. R. Dean, R. Sobash, 2008: Severe-weather forecast guidance from the first generation of large domain convection-allowing models: Challenges and opportunities. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor Soc., CD-ROM, 12.1. [Available from John Kain, NSSL, 120 David L. Boren Blvd., Norman, OK, USA, 73072.]

Kain, J. S., S. J. Weiss, M. E. Baldwin, 2006: The value of collaboration between researchers and forecasters in the development of NWP models. Preprints, The 4th Joint Korea-U. S. Workshop on Mesoscale Observation, Data Assimilation, and Modeling for Severe Weather, Seoul, Republic of Korea, Korea Science and Engineering Foundation/U.S. National Science F, 6.5. [Available from John Kain, NSSL, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Kain, J. S., S. J. Weiss, M. E. Baldwin, 2006: The value of collaboration between researchers and forecasters in the development of NWP models. Preprints, The 4th Joint Korea-U. S. Workshop on Mesoscale Observation, Data Assimilation, and Modeling for Severe Weather, Seoul, Republic of Korea, Korea Science and Engineering Foundation/U.S. National Science F, 6.5. [Available from John Kain, NSSL, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Kain, J. S., M. Xue, M. C. Coniglio, S. J. Weiss, F. Kong, T. L. Jensen, B. G. Brown, J. Gao, K. Brewster, K. W. Thomas, Y. Wang, C. S. Schwartz, J. J. Levit, 2010: Assessing advances in the assimilation of radar data within a collaborative forecasting-research environment. Weather and Forecasting, 25, 1510-1521.

The impacts of assimilating radar data and other mesoscale observations in real-time, convection-allowing model forecasts were evaluated during the spring seasons of 2008 and 2009 as part of the Hazardous Weather Test Bed Spring Experiment activities. In tests of a prototype continental U.S.-scale forecast system, focusing primarily on regions with active deep convection at the initial time, assimilation of these observations had a positive impact. Daily interrogation of output by teams of modelers, forecasters, and verification experts provided additional insights into the value-added characteristics of the unique assimilation forecasts. This evaluation revealed that the positive effects of the assimilation were greatest during the first 3–6 h of each forecast, appeared to be most pronounced with larger convective systems, and may have been related to a phase lag that sometimes developed when the convective-scale information was not assimilated. These preliminary results are currently being evaluated further using advanced objective verification techniques.

Kain, J. S., S. R. Dembek, S. J. Weiss, J. L. Case, J. J. Levit, R. A. Sobash, 2010: Extracting unique information from high resolution forecast models: Monitoring selected fields and phenomena every time step. Weather and Forecasting, 25, 1536-1542.

A new strategy for generating and presenting model diagnostic fields from convection-allowing forecast models is introduced. The fields are produced by computing temporal-maximum values for selected diagnostics at each horizontal grid point between scheduled output times. The two-dimensional arrays containing these maximum values are saved at the scheduled output times. The additional fields have minimal impacts on the size of the output files and the computation of most diagnostic quantities can be done very efficiently during integration of the Weather Research and Forecasting Model. Results show that these unique output fields facilitate the examination of features associated with convective storms, which can change dramatically within typical output intervals of 1–3 h.

Kaplan, M., C. Adaniya, P. Marzette, K. King, S. Underwood, J. Lewis, 2009: The role of upstream mid-tropospheric circulations in Sierra Nevada leeside (spillover precipitation): Part II: Secondary atmospheric river accompanying a mid-level jet. J. Hydrometeor., 10, 1327-1354.

Kaplan, M. L., R. K. Vellore, J. M. Lewis, M. Young, 2011: The role of unbalanced mesoscale circulations in dust storms. Journal of Geophysical Research - D: Atmospheres, 116, 218-247.

In this study, two dust storms in northwestern Nevada (February 2002 and April 2004) are investigated through the use of Weather Research and Forecasting (WRF) model simulations. The focus of the study is twofold: (1) Examination of dynamic processes on the meso‐b scale for both cases, and (2) analysis of extreme upper‐air cooling prior to storm formation and the development of a nearly discontinuous gust front in the 2002 case that could not be validated in an earlier synoptic‐scale study. Results of the simulations suggest that the driving mechanism for dust storm dynamics derives from the breakdown and subsequent balance between the advection of geostrophic wind and total wind in the exit region of the polar jet. In this process, the deviation from quasi‐geostrophic (Q‐G) balance creates a plume of ascent along and to the right of the jet’s exit region. The cold pool generation in the mid‐lower troposphere in consequence of this adjustment sets up the kinetic energy in the planetary boundary layer and creates a forward leaning (slope from north to south) cold front under the jet exit region. Surface heating is coupled with this frontal structure, and rapid surface pressure falls (rises) occur initially (later) in response to diabatic (adiabatic) processes. The adjustments occur at fast time scales, scales that are radically different from those in studies that followed the Q‐G tenets of the Danielsen paradigm. The results of this study indicate that meso‐b scale features associated with subgeostrophy in the exit region of the curved jet aloft and associated thermal wind imbalance (700–500 hPa) lead to significant velocity divergence aloft. Mass/momentum adjustments and the associated cooling strengthen the baroclinic zone aloft. The restoration to thermal wind balance accompanying this cooling resulted in a narrow zone of surface pressure rise and strong low‐level isallobaric winds. The turbulent momentum for dust ablation comes

Killeen, T. J., M. W. Douglas, T. Consiglio, P. M. Jorgensen, J. F. Mejia, 2007: Dry Spots and Wet Spots in the Andean hotspot. Journal of Biogeography, 34, 1357-1373.

Aim To explain the relationship between topography, prevailing winds and precipitation in order to identify regions with contrasting precipitation regimes and then compare floristic similarity among regions in the context of climate change.

Location Eastern slope of the tropical Andes, South America.

Methods We used information sources in the public domain to identify the relationship between geology, topography, prevailing wind patterns and precipitation. Areas with contrasting precipitation regimes were identified and compared for their floristic similarity.

Results We identify spatially separate super-humid, humid and relatively dry regions on the eastern slope of the Andes and show how they are formed by the interaction of prevailing winds, diurnally varying atmospheric circulations and the local topography of the Andes. One key aspect related to the formation of these climatically distinct regions is the South American low-level jet (SALLJ), a relatively steady wind gyre that flows pole-ward along the eastern slopes of the Andes and is part of the gyre associated with the Atlantic trade winds that cross the Amazon Basin. The strongest winds of the SALLJ occur near the 'elbow of the Andes' at 18° S. Super-humid regions with mean annual precipitation greater than 3500 mm, are associated with a 'favourable' combination of topography, wind-flow orientation and local air circulation that favours ascent at certain hours of the day. Much drier regions, with mean annual precipitation less than 1500 mm, are associated with 'unfavourable' topographic orientation with respect to the mean winds and areas of reduced cloudiness produced by local breezes that moderate the cloudiness. We show the distribution of satellite-estimated frequency of cloudiness and offer hypotheses to explain the occurrence of these patterns and to explain regions of anomalously low precipitation in Bolivia and northern Peru. Floristic analysis shows that overall similarity among all circumscribed regions of this study is low; however, similarity among super-humid and humid regions is greater when compared with similarity among dry regions. Spatially separate areas with humid and super-humid precipitation regimes show similarity gradients that are correlated with latitude (proximity) and precipitation.

Main conclusions The distribution of precipitation on the eastern slope of the Andes is not simply correlated with latitude, as is often assumed, but is the result of the interplay between wind and topography. Understanding the phenomena responsible for producing the observed precipitation patterns is important for mapping and modelling biodiversity, as well as for interpreting both past and future climate scenarios and the impact of climate change on biodiversity. Super-humid and dry regions have topographic characteristics that contribute to local climatic stability and may represent ancestral refugia for biodiversity; these regions are a conservation priority due to their unique climatic characteristics and the biodiversity associated with those characteristics.

Koch, S. E., B. S. Ferrier, M. T. Stoelinga, E. Szoke, S. J. Weiss, J. S. Kain, 2005: The use of simulated radar reflectivity fields in the diagnosis of mesoscale phenomena from high-resolution WRF model forecasts. Preprints, 11th Conference on Mesoscale Processes, Albuquerque, NM, USA, Amer. Meteor. Soc., CD-ROM, J4J.7. [Available from Steve Koch, ESRL, Boulder, CO, USA.]

The use of composite radar reflectivity fields (i.e., the maximum reflectivity in the grid column) as a model output product has become increasingly popular recently as a means for display of high-resolution numerical model fields, mainly for convective weather scenarios. This past winter, simulated radar reflectivity fields were produced for 5-km WRF model forecasts during the DTC (Developmental Testbed Center) Winter Forecast Experiment (DWFE). In addition, model reflectivity fields from 2-km and 4-km WRF forecasts were utilized during the annual Storm Prediction Center/National Severe Storms Laboratory (NSSL) Spring Program. The reflectivity product offers significant advantages over traditional precipitation forecast displays, including the obvious fact that radar reflectivity is easier to verify in real time by directly comparing with readily available, observed composite reflectivity products. It has also recently become possible to compare model forecast radar reflectivity fields to a high quality, three-dimensional, national radar reflectivity mosaic product on a 1-km Cartesian grid being developed at NSSL. The chief advantage of the model reflectivity product appears to be that it allows one to more easily see detailed mesoscale and near-stormscale structures capable of being forecast by finer resolution models, such as lake-effect snowbands, the structure of deep convection, and frontal precipitation bands. Examples demonstrating this advantage will be presented at the conference for a variety of mesoscale phenomena.

Before one can have confidence in the meaning of simulated reflectivity factor fields for interpretation of mesoscale models, it is important to understand how they are determined. The equivalent reflectivity factor is computed from the forecast mixing ratios of grid-resolved hydrometeor species, assuming Rayleigh scattering by spherical particles of known density and an exponential size distribution. During the DWFE, perceptible differences appeared in the general nature of the simulated reflectivity fields from the two WRF models, most notably a greater coverage of reflectivity below ~25 dBZ and higher maximum reflectivities in the case of the NMM compared to the ARW for winter storms. However, when attention focused on severe convective weather regions during the Spring Program, the NMM produced noticeably lower values of maximum reflectivity compared to the ARW versions, with the NMM values limited to less than 50 dBZ. These differences are mostly explained by the differences in physics packages, particularly the way various liquid water and ice species are treated in the model microphysics schemes. The WRF Single-Moment 5-class (“WSM5”) microphysics scheme used for the WRF-ARW model during DWFE treats the cloud condensate in the form of cloud water and cloud ice as a combined category, and precipitation in the form of rain and snow also as a combined category. The WRF-NMM used the Ferrier microphysics scheme, which accounts for four classes of hydrometeors. The most important difference between the two microphysical parameterizations concerns the assumed size distributions for snow: for the same snow mass content, differences in radar reflectivity will scale with differences in parameterized snow number concentrations between the two microphysical schemes.

It is also important to understand that it is not possible to make a strictly valid comparison between composite reflectivity computed from a model grid point and that measured by scanning radar. Owing to the fact that the radar resolution degrades with distance from the transmitter, that scanning radars cannot detect hydrometeors in the lower atmosphere due to the earth's curvature effect, and numerous other considerations (including ground clutter near the radar, anomalous propagation, etc.), any attempt to make direct comparisons between the model simulated reflectivity fields and radar measurements is replete with problems, though the NSSL product is experimenting with novel ways to overcome these problems.

Available online at http://ams.confex.com/ams/pdfpapers/97032.pdf.

Kong, F., M. XUE, D. R. Bright, M. C. Coniglio, K. W. Thomas, Y. Wang, D. Weber, J. S. Kain, S. J. Weiss, J. Du, 2007: Preliminary analysis on the real-time storm-scale ensemble forecasts produced as a part of the NOAA Hazardous Weather Testbed 2007 Spring Experiment.. Preprints, Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc, CD-ROM, 3B.2.

Kong, F., M. Xue, D. R. Bright, M. C. Coniglio, K. W. Thomas, Y. Wang, D. B. Weber, J. S. Kain, S. J. Weiss, J. Du, 2007: Preliminary analysis on the real-time storm-scale ensemble forecasts produced as a part of the NOAA Hazardous Weather Testbed 2007 Spring Experiment. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 3B.2. [Available from Fanyou Kong, CAPS, 120 David L. Boren Blvd., Norman, OK, USA, 73072.]

A real-time storm-scale WRF-ARW-based ensemble forecast system at 4-km resolution is being developed at CAPS and will be run daily for 33 hours as part of the NOAA Hazardous Weather Testbed (HWT) 2007 Spring Experiment, for a domain covering the eastern 2/3 of the continental U.S. This pilot system consists of ten hybrid perturbation members that consist of a combination of perturbed initial conditions and various microphysics and PBL physics parameterization schemes. The design considerations and the scientific questions that the system intends to address will be presented and discussed.

In addition to traditional ensemble products widely used in large-scale and mesoscale ensemble forecasting systems, such as the mean, spread, and probability of selected forecast fields, emphases are given to the generation and assessment of products specific to storm-scale, cloud-resolving ensemble forecasts. Such products include but are not limited to: probability of storm type (e.g., linear vs. cellular), large hail probability, icing potential (high super-cooled water content probability), damaging wind gusts at surface, reflectivity exceedance, updraft rotation, and supercell thunderstorm detection in the form of probability or joint probability for Supercell Composite Parameter, Significant Tornado Parameter, Supercell Detection Index, and Updraft Helicity. Many of these products are created in real time through existing capabilities in the SPC version of the N-AWIPS system for the use and evaluation by researchers and operational forecasters during the experiment. The statistical consistency of the ensemble system, in terms of spread-error relation, is assessed using the two-months of data after the experiment. The performance of the ensemble forecasts, in terms of quantitative skill scores, is compared with the NCEP operational SREF and 12 km NAM forecasts, and a CAPS 2-km WRF forecast over the same domain and period. Skill scores for sub-groups of the ensemble will be examined to assess the effectiveness of initial condition and physics perturbations.

Available online at http://ams.confex.com/ams/pdfpapers/124667.pdf.

Kong, F., M. Xue, K. W. Thomas, Y. Wang, J. S. Kain, S. J. Weiss, D. R. Bright, J. Du, K. K. Droegemeier, 2008: Real-Time Storm-Scale Ensemble Forecast 2008 Spring Experiment. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., CD-ROM, 12.3. [Available from Fanyou Kong, CAPS, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Available online at http://ams.confex.com/ams/24SLS/techprogram/paper_141827.htm.

Kong, F., M. Xue, K. W. Thomas, Y. Wang, K. A. Brewster, J. Gao, K. K. Droegemeier, J. S. Kain, S. J. Weiss, D. R. Bright, M. C. Coniglio, J. Du, 2009: A real-time storm-scale ensemble forecast system: 2009 Spring Experiment. Preprints, 23rd Conference on Weather Analysis and Forecasting/19th Conference on Numerical Weather Prediction, Omaha, NE, USA, Amer. Meteor. Soc., CD-ROM, 16A.3. [Available from Fanyou Kong, CAPS, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Available online at http://ams.confex.com/ams/23WAF19NWP/techprogram/paper_154118.htm.

Koracin, D., J. Businger, C. Dorman, J. Lewis, 2005: Formation, evolution, and dissipation of coastal sea fog. Bound.-Layer Meteorol., 117, 447-478.

Koracin, D., D. Leipper, J. Lewis, 2005: Modeling sea fog on the U. S. California coast during a hot spell event. Geofizika, 22, 59-82.

Koracin, D., J. Businger, C. Dorman, J. Lewis, 2005: Formation, evolution, and dissipation of coastal sea fog. Bound. - Layer Meteorol., 117, 447-478.

Koracin, D., D. Liepper, J. Lewis, 2005: Modeling sea fog on the U. S. California coast during a hot spell event. Geofizika, 22, 59-82.

Krehbiel, P., W. Rison, R. Thomas, D. MacGorman, W. D. Rust, T. Marshall, M. Stolzenburg, 2006: A review of lightning phenomenology in thunderstorms. Preprints, 2nd Conference on Meteorological Applications of Lightning Data, Atlanta, GA, USA, American Meteorological Society, 6.2.

Kuhlman, K. M., C. L. Ziegler, E. R. Mansell, D. R. MacGorman, J. M. Straka, 2006: Numerically Simulated Electrification and Lightning of the 29 June 2000 STEPS Supercell Storm. Monthly Weather Review, 134, 2734-2757.

A three-dimensional dynamic cloud model incorporating airflow dynamics, microphysics, and thunderstorm electrification mechanisms is used to simulate the first 3 h of the 29 June 2000 supercell from the Severe Thunderstorm Electrification and Precipitation Study (STEPS). The 29 June storm produced large flash rates, predominately positive cloud-to-ground lightning, large hail, and an F1 tornado. Four different simulations of the storm are made, each one using a different noninductive (NI) charging parameterization. The charge structure, and thus lightning polarity, of the simulated storm is sensitive to the treatment of cloud water dependence in the different NI charging schemes. The results from the simulations are compared with observations from STEPS, including balloon-borne electric field meter soundings and flash locations from the Lightning Mapping Array. For two of the parameterizations, the observed “inverted” tripolar charge structure is well approximated by the model. The polarity of the ground flashes is opposite that of the lowest charge region of the inverted tripole in both the observed storm and the simulations. Total flash rate is well correlated with graupel volume, updraft volume, and updraft mass flux. However, there is little correlation between total flash rate and maximum updraft speed. Based on the correlations found in both the observed and simulated storm, the total flash rate appears to be most representative of overall storm intensity.

Available online at http://www.ametsoc.org.

Kuhlman, K., D. MacGorman, M. Biggerstaff, W. D. Rust, T. Schuur, C. Ziegler, P. Krehbiel, 2006: Lightning and radar observatons of the 29 May 2004 supercell during TELEX. Preprints, 2nd Conference on Meteorological Applications of Lightning Data, Atlanta, GA, USA, American Meteorological Society, 3.3.

Kuhlman, K. M., E. R. Mansell, C. L. Ziegler, M. I. Biggerstaff, D. R. MacGorman, D. C. Dowell, 2008: EnKF data assimilation and dual-Doppler analysis of the 29 May 2004 Geary, Oklahoma supercell. Proc. 24th Conference on Severe Local Storms, Savannah, GA, USA, American Meteorological Society, P5.1.

On 29 May 2004, a long-track supercell storm moved across Oklahoma producing multiple tornadoes and numerous reports of large hail. Two mobile, C-band, Doppler (SMART-R) radars collected data in 2.5 min volume scans almost continuously for more than three hours. Dual-Doppler analyses were completed for select times using a1 km grid spacing and a 2-pass Barnes objective analysis in the interpolation of radial velocities and reflectivity to a Cartesian grid following Majcen et al (2008).

The focus of the radar data assimilation for this study is to retrieve the state of the storm rather than to develop forecast applications. For this purpose, the ensemble Kalman filter (EnKF) technique is used to assimilate reflectivity and/or radial velocity data into the model from SMART radar at approximately five minute intervals. Comparisons of the simulations employing EnKF to a simulation without data assimilation and to the dual-Doppler syntheses at various times of the storm's life-cycle will be presented. These results will be used to quantify the agreement between the simulation and the observations providing background such that future studies may use the simulations in order to to retrieve unobserved fields.

Available online at http://ams.confex.com/ams/24SLS/techprogram/paper_142031.htm.

Kuhlman, K. M., D. R. MacGorman, E. R. Mansell, C. L. Ziegler, M. I. Biggerstaff, 2010: A SIMULATION OF ELECTRIFICATION AND LIGHTNING IN A SUPERCELL STORM USING ENKF TO ASSIMILATE DOPPLER RADAR OBSERVATIONS. Proc. International Lightning Meteorology Conferance, Orlando, FL, USA, Vaisala, 1-8.

Available online at http://www.vaisala.com/Vaisala%20Documents/Scientific%20papers/14.Kuhlman,%20MacGorman,%20Mansell.pdf.

Kuhlman, K. M., E. R. Mansell, D. R. MacGorman, C. L. Ziegler, M. I. Biggerstaff, 2010: Electrification and Lightning in Simulations of the 29 May 2004 Geary, OK Storm Using EnKF Data Assimilation. Extended Abstracts, 25th Conference on Severe Local Storms, Denver, CO, USA, American Meteorological Society, 13A.7.

On 29 May 2004, a line of convective cells formed along a dryline near Elk City, OK; one intensified to a heavy-precipitation (HP) supercell north of Weatherford, OK as it moved into the TELEX domain (MacGorman et al. 2008). The data set established through this field campaign provides an excellent opportunity for using Ensemble Kalman Filter (EnKF) assimilation of radar data to produce a storm simulation having characteristics similar to those of the observed storm, so that we can examine hypotheses concerning the storm's electrification and lightning.

The Collaborative Model for Multiscale Atmospheric Simulation (COMMAS) was used to produce the simulations. Radial velocity and reflectivity data from a single mobile doppler radar were assimilated into the the COMMAS model using two-moment microphysics, including seven hydrometeor categories, and parameterizations for electrification and lightning with a horizontally homogeneous base state. The simulated precipitation and wind fields were similar to those of the observed storm. Simulated lightning flash rates were very large, as was observed, and the distribution of charge in the main body of the storm revealed in the simulation details the lightning dependence on storm kinematics that could not be directly observed. The simulation produced the observed lightning holes and the high-altitude lightning seen in the observations. However, the simulation failed to produce the observed lightning initiations (or even lightning channels) in the distant downstream anvil; instead, the simulated lightning was confined to the main body of the storm.

Kunkel, K. E., P. Bromirski, H. E. Brooks, T. Cavazos, A. V. Douglas, D. R. Easterling, K. A. Emanuel, P. Y. Groisman, G. J. Holland, T. R. Knutson, J. P. Kossin, P. D. Komar, D. H. Levinson, R. L. Smith, J. Allan, R. Assel, S. Changnon, J. Lawrimore, K. B. Liu, T. Peterson, 2008: Observed Changes in Weather and Climate Extremes. Weather and Climate Extremes in a Changing Climate. Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands. Synthesis and Assessment Product 3.3 Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change, T. M. Karl, G. A. Meehl, C. D. Miller, S. J. Hassol, A. M. Waple, W. L. Murray, Ed(s)., U.S. Climate Change Science Program and the Subcommittee on Glob, 35-80.

Ladwig, W. C., D. J. Stensrud, 2009: Relationship between Tropical Easterly Waves and Precipitation during the North American Monsoon. J. Climate, 22, 258-271.

Relationships between tropical easterly waves (TEWs) and precipitation over Mexico and the United States are examined during the North American monsoon (NAM). The National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis data are used to identify 137 TEWs that cross Mexico north of 20N after monsoon onset over a 31-yr period from 1975 to 2005. Mean precipitation anomalies over two-day periods both before and after TEW passage are determined using Climate Prediction Center daily precipitation analyses. Results indicate that positive precipitation anomalies occur along the west coast of Mexico and extending into the west-central United States in association with TEW passage. Negative precipitation anomalies are found in the south-central United States. These precipitation anomaly patterns share many similarities to precipitation anomaly patterns previously defined in association with gulf surge events. On longer time scales, correlations between the total number of these northern TEWs crossing Mexico and 90-day monsoon period precipitation anomalies are also examined. An out-of-phase relationship is found between monsoon period precipitation anomalies in the southwestern and south-central United States, suggesting that increasing the number of northern TEWs crossing Mexico leads to enhanced monsoon period rainfall in Arizona and New Mexico and reduced monsoon period rainfall in Texas and Oklahoma. Thus, these northern TEWs likely play an important role in producing the distribution of precipitation throughout the NAM region and the south-central United States during the monsoon season, and extended- range predictions of northern TEW frequency may lead to improved seasonal rainfall anomaly forecasts in these regions.

Lakshmanan, V., J. J. Gourley, Z. Flamig, S. Giagrande, 2009: A simple data-driven model for streamflow prediction. Preprints, 6th Conference on Artificial Applications to the Environmental Sciences, Phoenix, AZ, USA, Amer. Meteor. So, CD-ROM, J6.2.

Lakshmanan, V., J. Kain, 2010: A Gaussian Mixture Model Approach to Forecast Verification. Weather and Forecasting, 25, 908-920.

Verification methods for high-resolution forecasts have been based either
on filtering or on objects created by thresholding the images.
The filtering methods do not easily permit the use of
deformation while identifying objects based on thresholds can be problematic.
In this paper, we introduce a new approach in which the
observed and forecast fields are broken down into a mixture of Gaussians, and
the parameters of the Gaussian Mixture Model fit are examined
to identify translation, rotation and scaling errors.
We discuss the advantages of this method in
terms of the traditional filtering or object-based methods and
interpret resulting scores on a standard verification dataset.

Available online at http://cimms.ou.edu/~lakshman/Papers/gmmverif.pdf.

Lakshmanan, V., J. S. Kain, 2010: Model Verification Using Gaussian Mixture Models. Preprints, 20th Conference on Probability and Statistics in the Atmospheric Sciences, Atlanta, GA, USA, Amer. Meteor. Soc., 6.4.

Lakshmanan, V., J. Kain, 2010: A Gaussian mixture model approach to forecast verification. Weather and Forecasting, 25, 908-920.

We introduce a new approach in which the observed and forecast fields are broken down into a mixture of Gaussians and the parameters of the Gaussian Mixture Model fit are examined to identify translation, rotation and scaling errors. We discuss the advantages of this method in terms of the traditional filtering or object-based methods and interpret resulting scores on a standard verification dataset.

Available online at http://cimms.ou.edu/%7Elakshman/Papers/gmmverif.pdf.

Lakshmanan, V., j. Kain, 2010: Model verification using gaussian mixture models. Extended Abstracts, 20th Conference on Probability and Statistics in the Atmospheric Sciences, Atlanta, GA, USA, Amer. Meteor. Soc., CD-ROM, 6.4.

Lakshmanan, V., R. Rabin, J. Otkin, J. Kain, 2012: Approximating radiative transfer with a neural network. Preprints, 10th Conf. on Artificial Intelligence App. to Env. Sci., Norman, OK, USA, AMS, CD-ROM, TJ14.3.

We demonstrate that it is possible to approximate the radiative transfer model using an universal approximator whose parameters can be determined by fitting the output of the forward model to inputs derived from the model forecasts from which it was computed. The resulting approximation is very close to the complex radiative transfer model and has the advantage that it can be computed in a matter of minutes. This approximation is carried out on model forecasts to demonstrate its utility as a visualization and forecasting tool.

Lakshmanan, V., R. Rabin, J. Kain, J. Otkin, S. Dembek, 2012: Visualizing Model Data Using A Fast Approximation of a Radiative Transfer Model. Journal of Atmospheric and Oceanic Technology, 29, 745-754.

Visualizing model forecasts using simulated satellite imagery has proven very useful because the depiction of forecasts using cloud imagery can provide inferences about meteorological scenarios and
physical processes that are not characterized well by depictions of those forecasts using radar reflectivity. A forward radiative transfer model is capable of providing such a visible-channel depiction of numerical weather prediction model output, but present-day forward models are too slow to run routinely on operational model forecasts.

It is demonstrated that it is possible to approximate the radiative transfer model using an universal approximator whose parameters can be determined by fitting the output of the forward model to inputs derived from the raw output from the prediction model. The resulting approximation is very close to the result derived from the complex radiative transfer model and has the advantage that it can be computed in a
small fraction of the time required by the forward model. This approximation is carried out on model forecasts to demonstrate its utility as a visualization and forecasting tool.

Available online at http://cimms.ou.edu/~lakshman/Papers/visnn.pdf.

Lakshmivarahan, S., D. J. Stensrud, 2009: Ensemble Kalman Filter: Application to Meteorological Data Assimilatioin. IEEE Control Systems Magazine, 29, 34-46.

Lakshmivarahan, S., J. M. Lewis, 2010: Forward Sensitivity Approach to Dynamic Data Assimilation. Advances in Meteorology, 2010, 1-13.

The least squares fit of observations with known error variance to a strong-constraint dynamical model has been developed through use of the time evolution of sensitivity functions – the derivatives of model output with respect to the elements of control (initial conditions, boundary conditions, and physical/empirical parameters). Model error is assumed to stem from incorrect specification of the control elements. The optimal corrections to control are found through solution to an inverse problem. Duality between this method and the standard 4D-Var assimilation using adjoint equations has been proved. The paper ends with an illustrative example based on a simplified version of turbulent heat transfer at the sea/air interface.

Lengyel, M. M., H. E. Brooks, R. L. Holle, M. A. Cooper, 2005: Lightning casualties and their proximity to surrounding cloud-to-ground lightning. Preprints, 14th Symposium on Education, San Diego, CA, USA, American Meteorological Society, CD-ROM, P1.35.

Lengyel, M., M. A. Cooper, R. Holle, H. E. Brooks, 2010: The role of multidisciplinary teams and public education in reducing lightning casualties worldwide. Proc. 30th International Conference on Lightning Protection, Cagliari, Italy, IEEE, SSB-1329. [Available from macooper@uic.edu,

In the past century, lightning killed more people in the United States on average annually than any other storm situation except floods. However, due to persistent lightning safety efforts by a multidisciplinary team, the annual National Lightning Safety Awareness Week campaign, shifts in population from rural to urban areas, and improved grounding of buildings, US lightning deaths have decreased to an average of less than 50 per year over the past decade. This demonstrates that aggressive public education can have a significant role in reducing lightning deaths and injuries.

Lewis, J., 2005: Roots of ensemble forecasting. Monthly Weather Review, 133, 1865-1885.

Lewis, J., R. Maddox, C. Crisp, 2006: Architect of severe storms forecasting: Colonel Robert C. Miller. Bulletin of the American Meteorological Society, 87, .

Lewis, J. M., 2007: Use of a mixed-layer model to investigate problems in operational prediction of return flow. Monthly Weather Review, 135, 2610-2628.

Lewis, J. M., 2007: A Forecaster's Story: Robert H. Johns. Electronic Journal of Severe Storm Meteorology, 2, 1-19.

The stages in the life of a severe storms forecaster, Robert H. Johns, are reconstructed from information in a series of interviews with him. The traditional interview format, question-and-answer mode, has been converted to a first-person narrative that leads to a more-continuous train of thought.
The storyline begins by describing Johns’ entrainment into meteorology as a youngster. By virtue of his contact and conversations with farmers in rural Indiana, he became interested in weather’s impact on the farmers and their crop yields. Early stimulation also came from a challenging weather project in the 6th grade and reading George Stewart’s novel Storm. From these experiences, Bob Johns decided to pursue a science career in service to society. This service took the form of work as a weather forecaster for the United States Weather Bureau (USWB)/National Weather Service (NWS).
The arduous path to severe storms forecaster is traced by highlighting his youthful experiences, his academic training, and the stepwise progression from student trainee to lead forecaster at the Severe Local Storms (SELS) unit of the USWB/NWS.

Available online at http://ejssm.org/ojs/index.php/ejssm/article/view/29/32.

Lewis, J. M., S. Lakshmivarahan, 2008: Sasaki's Pivotal Contribution: Calculus of Variations Applied to Weather Map Analysis. Monthly Weather Review, 136, 3553-3567.

Yoshikazu Sasaki developed a variational method of data assimilation, a cornerstone of modern-day analysis and prediction in meteorology. Fundamentally, he formulated data assimilation as a constrained minimization problem with equality constraints. The generation of this idea is tracked by analyzing his education and research at the University of Tokyo in the immediate post-WWII period. Despite austere circumstances — including limited financial support for education, poor living conditions, and a lack of educational resources — Sasaki was highly motivated and overcame these obstacles on his path to developing this innovative method of weather map analysis. We follow the stages of his intellectual development where information comes from access to his early publications, oral histories, and letters of reminiscence.
It has been argued that Sasaki’s unique contribution to meteorological data assimilation stems from his deterministic view of the problem – a view founded on the principles of variational mechanics. Sasaki’s approach to the problem is compared and contrasted with the stochastic view that was pioneered by Arnt Eliassen. Both of these optimal approaches are viewed in the context of the pragmatic/operational objective analysis schemes that were developed in the 1950s – 1960s. Finally, current-day methods, 3D-Var and 4D-Var, are linked to the optimal methods of Eliassen and Sasaki.

Lewis, J. M., 2008: Book Review: The Emergence of Numerical Weather Prediction: Richardson's Dream. Bulletin of the American Meteorological Society, 89, 1178-1179.

Lewis, J. M., S. Lakshmivarahan, S. Dhall, 2006: Dynamic Data Assimilation: A Least Squares Approach. Cambridge University Press, 654 pp.

NOAA Outstanding Publication Award in 2006

Lewis, J., 2008: Smagorinsky's GFDL; Building the team. Bulletin of the American Meteorological Society, 89, 1339-1353.

Joseph Smagorinsky (1924 - 2005) was a forceful and powerful figure in meteorology during the last half of the twentieth century. He served as director of the Geophysical Fluid Dynamics Laboratory (GFDL) for nearly thirty years (1955 - 1983); and during his tenure as director, this organization substantially contributed to advances in weather forecasting and climate diagnostics/prediction. The purpose of this research is to explore Smagorinsky’s philosophy of science and style of management that were central to the success of GFDL. Information comes from his early scientific publications, personal letters and notes in the possession of his family, several oral histories, and letters of reminiscence from scientists who worked within and outside GFDL.
The principal results of the study are: (1) early inspiration and development of Smagorinsky’s scientific philosophy came from his contact with Jule Charney and Harry Wexler, (2) his doctoral dissertation ideally prepared him for appointment as director of the U. S. Weather Bureau’s long-range numerical prediction project in 1955 — the General Circulation Research Section [later renamed GFDL], (3) he masterfully assembled a team of researchers to attack the challenging problem of general circulation modeling, and (4) he exhibited an authoritarian style of rule tempered by protection of the scientists from disrupting outside influence while celebrating the elitism and esprit de corps that characterized the laboratory.
A list of Smagorinsky’s management principles is found in the Appendix. Several of these tenets have been interspersed in the main body of the paper in support of actions he took at GFDL.

Lewis, J. M., 2009: Sasaki's Pathway to Deterministic Data Assimilation. Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications, S. K. Park, L. Xu, Ed(s)., Springer, 1-19.

Yoshikazu Sasaki developed the variational method of data assimilation, a cornerstone of modern-day analysis and prediction in meteorology. The generation of this idea is tracked by analyzing his education at the University of Tokyo in the immediate post-WWII period. Despite austere circumstances — including limited financial support for education, poor living conditions, and a lack of educational resources — Sasaki was highly motivated and overcame these obstacles on his path to developing this innovative method of weather map analysis. We follow the stages of his intellectual development where information comes from access to his early publications, oral histories, letters of reminiscence, and biographical data from the University of Tokyo and the University of Oklahoma. Based on this information, key steps in the development of his idea were: (1) a passion for science in his youth, (2) an intellectually stimulating undergraduate education in physics, mathematics, and geophysics, (3) a fascination with the theory of variational mechanics, and (4) a ‘bridge to America’ and the exciting new developments in numerical weather prediction (NWP).
A comparison is made between Sasaki’s method and Optimal Interpolation (OI), a contemporary data assimilation strategy based on the work of Arnt Eliassen and Lev Gandin. Finally, a biographical sketch of Sasaki including his scientific genealogy is found in the appendix.

Lewis, J. M., D. Martin, R. Rabin, H. Moosmuller, 2010: Suomi: Pragmatic Visionary. Bulletin of the American Meteorological Society, 91, 561-577.

The steps on Verner Suomi's path to becoming a research scientist are examined. We argue that his research style – his natural interests in science and engineering, and his methodology in pursuing answers to scientific questions – was developed in his youth on the Iron Range of northeastern Minnesota, as an instructor in the cadet program at the University of Chicago (U of C) during World War II and as a fledgling academician at University of Wisconsin - Madison. We examine several of his early experiments that serve to identify his style. The principal results of the study are: 1) despite austere living conditions on the Iron Range during the Great Depression, Suomi benefitted from excellent industrial arts courses at Eveleth High School; 2) with his gift for designing instruments, his more practical approach to scientific investigation flourished in the company of world-class scientific thinkers at U of C; 3) his dissertation on the heat budget over a cornfield in the mid-1950s served as a springboard for studying the Earth-atmosphere energy balances in the space-age environment of the late 1950s; and 4) his design of radiometers – the so-called ping-pong radiometer and its sequel, the hemispheric bolometer – flew aboard Explorer VI and VII in the late 1950s, and analysis of the radiances from these instruments led to the first accurate estimate of the Earth's mean albedo.

Lewis, J. M., M. L. Kaplan, R. K. Vellore, R. M. Rabin, J. Hallett, S. A. Cohn, 2011: Dust Storm over the Black Rock Desert: Larger-scale Dynamic Signatures. Journal of Geophysical Research - D: Atmospheres, 116, 1-23.

A dust storm that originated over the Black Rock Desert (BRD) of northwestern Nevada is investigated. Our primary goal is to more clearly understand the sequence of dynamical processes that generate surface winds responsible for entraining dust from this desert. In addition to reliance on conventional surface and upper-air observations, we make use of reanalysis datasets (NCAR/NCEP and NARR) — blends of primitive equation model forecasts and observations. From these datasets, we obtain the evolution of vertical motion patterns and ageostrophic motions associated with the event. In contrast to earlier studies that have emphasized the importance of indirect transverse circulations about an upper-level jet streak, our results indicate that the transition from indirect to direct circulation across the exit region of upper-level jet streak is central to creation of low-level winds that ablate dust from the desert. It is further argued that the transition of vertical circulation patterns is in response to adjustments to geostrophic imbalance — where the adjustment time scale is the order of 6-9 h. Although unproven, we suggest that precedent rainfall over the alkali desert two weeks prior to the event was instrumental in lowering the bulk density of sediments and thereby improved the chances for dust ablation. We comprehensively compare/contrast our results with those of earlier investigators, and we present an alternative view of key dynamical signatures in atmospheric flow that portend the likelihood of dust storms over the western United States.

Liang, X. Z., M. Xu, K. E. Kunkel, G. A. Grell, J. S. Kain, 2007: Regional Climate Model Simulation of U.S.–Mexico Summer Precipitation Using the Optimal Ensemble of Two Cumulus Parameterizations. Journal of Climate, 20, 5201-5207.

Liu, S., C. Qiu, Q. Xu, P. Zhang, J. Gao, A. Shao, 2005: An improved method for Doppler wind and thermodynamic retrievals. Advances in Atmospheric Sciences, 22, 90-102.

Liu, S., Q. Xu, P. Zhang, 2005: Quality control of Doppler velocities contaminated by migrating birds. Part II: Bayes identification and probability tests. Journal of Atmospheric and Oceanic Technology, 22, 1114-1121.

Liu, L., P. Zhang, Q. Xu, F. Kong, S. Liu, 2005: Retrieval model of dual linear polarization radar observations from simulation model output. Adv. Atmos. Sci. 22, 711-719., 22, 711-719.

Liu, S., M. Xue, Q. Xu, 2007: Using wavelet analysis to detect tornadoes from doppler radar radial-velocity observations. Journal of Atmospheric and Oceanic Technology, 24, 344-359.

Liu, L., Q. Xu, P. Zhang, S. Liu, 2008: Automated Detection of Contaminated Radar Image Pixels in Mountain Areas. Adv. Atmos. Sci., 25, 778-790.

In mountain areas, radar observations are often contaminated (1) by echoes from high-speed moving vehicles and (2) by point-wise ground clutter under either normal propagation (NP) or anomalous propagation (AP) conditions. Level II data are collected from KMTX (Salt Lake City, Utah) radar to analyze these two types of contamination in the mountain area around the Great Salt Lake. Human experts provide the ``ground truth" for possible contamination of either type on each individual pixel. Common features are then extracted for contaminated pixels of each type. For example, pixels contaminated by echoes from high-speed moving vehicles are characterized by large radial velocity and spectrum width. Echoes from a moving train tend to have larger velocity and reflectivity but smaller spectrum width than those from moving vehicles on highways. These contaminated pixels are only seen in areas of large terrain gradient (in the radial direction along the radar beam). The same is true for the second type of contamination - point-wise ground clutters. Six quality control (QC) parameters are selected to quantify the extracted features. Histograms are computed for each QC parameter and grouped for contaminated pixels of each type and also for non-contaminated pixels. Based on the computed histograms, a fuzzy logical algorithm is developed for automated detection of contaminated pixels. The algorithm is tested with KMTX radar data under different (clear and rainy) weather conditions.

Liu, S., G. DiMego, K. V. Kumar, D. Keyser, S. Guan, Q. Xu, K. Nai, P. Zhang, L. Liu, J. Zhang, X. Xu, K. Howard, 2009: WSR-88D radar data processing at NCEP. Extended Abstracts, 34rd Conference on Radar Meteorology, Williamsburg, VA, USA, AMS, CD-ROM, 14.2.

Available online at http://ams.confex.com/ams/34Radar/techprogram/paper_156011.htm.

Lu, H., Q. Xu, 2009: Trade-offs between observation accuracy and resolutions in configuring phased-array radar velocity scans for ensemble-based storm-scale data assimilation. Journal of Applied Meteorology and Climatology, 48, 1230-1244.

Assimilation experiments are carried out with simulated radar radial-velocity observations to examine the impacts of observation accuracy and resolutions on storm-scale wind assimilation with an ensemble square root filter (EnSRF) on a storm-resolving grid (Δx = 2 km). In this EnSRF, the background covariance is estimated from an ensemble of 40 imperfect-model predictions. The observation error includes both measurement error and representativeness error, and the error variance is estimated from the simulated observations against the simulated “truth.” The results show that the analysis is not significantly improved when the measurement error is overly reduced (from 4 to 1 m s−1) and becomes smaller than the representativeness error. The analysis can be improved by properly coarsening the observation resolution (to 2 km in the radial direction) with an increase in measurement accuracy and further improved by properly enhancing the temporal resolution of radar volume scans (from every 5 to 2 or 1 min) with a decrease in measurement accuracy. There can be an optimal balance or trade-off between measurement accuracy and resolutions (in space and time) for configuring radar scans, especially phased-array radar scans, to improve storm-scale radar wind analysis and assimilation.

Lu, H., Q. Xu, M. Yao, S. Gao, 2011: Time-expanded sampling for ensemble-based filters: assimilation experiments with real radar observations. Advances in Atmospheric Sciences, 28, 743-757.

By sampling perturbed state vectors from each ensemble prediction run at properly selected time levels in the vicinity of the analysis time, the recently proposed time-expanded sampling approach can enlarge the ensemble size without increasing the number of prediction runs and, hence, can reduce the computational cost of an ensemble-based filter. In this study, this approach is tested for the first time with real radar data from a tornadic thunderstorm. In particular, four assimilation experiments were performed to test the time-expanded sampling method against the conventional ensemble sampling method used by ensemble-based filters. In these experiments, the ensemble square-root filter (EnSRF) was used with 45 ensemble members generated by the time-expanded sampling and conventional sampling from 15 and 45 prediction runs, respectively, and quality-controlled radar data were compressed into super-observations with properly reduced spatial resolutions to improve the EnSRF performances. The results show that the time-expanded sampling approach not only can reduce the computational cost but also can improve the accuracy of the analysis, especially when the ensemble size is severely limited due to computational constraints for real-radar data assimilation. These potential merits are consistent with those previously demonstrated by assimilation experiments with simulated data.

MacGorman, D., D. Rust, T. Schuur, M. Biggerstaff, J. Straka, C. Ziegler, E. Mansell, P. Krehbiel, W. Rison, T. Hamlin, L. Carey, E. Bruning, K. Kuhlman, N. Ramig, C. Payne, 2005: Lightning Relative to Storm Structure and Microphysics in TELEX. Polarimetric radar and electrical structure of a multicell storm. Preprints, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, 10R.7.

MacGorman, D., C. L. Ziegler, E. Mansell, W. Beasley, B. Fiedler, 2005: Retrieval and assimilation of storm characteristics from both in-cloud and cloud-to-ground lightning data to improve mesoscale model forecasts. Final report to the Office of Naval Research (ONR Grant # N00014-00-1-0525) 1, 54 pp.

MacGorman, D. R., W. D. Rust, T. J. Schuur, M. I. Biggerstaff, J. M. Straka, C. L. Ziegler, E. R. Mansell, E. C. Bruning, K. M. Kuhlman, N. R. Lund, N. S. Biermann, C. Payne, L. D. Carey, P. R. Krehbiel, W. Rison, K. B. Eack, W. H. Beasley, 2008: TELEX: The Thunderstorm Electrification and Lightning Experiment. Bulletin of the American Meteorological Society, 89, 997-1013.

The field program of the Thunderstorm Electrification and Lightning Experiment (TELEX) took place in central Oklahoma, May–June 2003 and 2004. It aimed to improve understanding of the interrelationships among microphysics, kinematics, electrification, and lightning in a broad spectrum of storms, particularly squall lines and storms whose electrical structure is inverted from the usual vertical polarity. The field program was built around two permanent facilities: the KOUN polarimetric radar and the Oklahoma Lightning Mapping Array. In addition, balloon-borne electric-field meters and radiosondes were launched together from a mobile laboratory to measure electric fields, winds, and standard thermodynamic parameters inside storms. In 2004, two mobile C-band Doppler radars provided high-resolution coordinated volume scans, and another mobile facility provided the environmental soundings required for modeling studies. Data were obtained from twenty-two storm episodes, including several small isolated thunderstorms, mesoscale convective systems, and supercell storms. Examples are presented from three storms. A heavy-precipitation supercell storm on 29 May 2004 produced greater than 3 flashes per second for 1.5 h. Holes in the lightning density formed and dissipated sequentially in the very strong updraft and bounded weak echo region of the mesocyclone. In a small squall line on 19 June 2004, most lightning flashes in the stratiform region were initiated in or near strong updrafts in the convective line and involved positive charge in the upper part of the radar bright band. In a small thunderstorm on 29 June 2004, lightning activity began as polarimetric signatures of graupel first appeared near lightning initiation regions.

Available online at http://ams.allenpress.com/archive/1520-0477/89/7/pdf/i1520-0477-89-7-997.pdf.

MacGorman, D. R., T. Mansell, C. Ziegler, J. Straka, 2008: Detailed storm simulations by a numerical cloud model with electrification and lightning parameterizations. Preprints, 20th International Lightning Detection Conference, Tucson, AZ, USA, Vaisala, 28.

We have further developed our three-dimensional cloud model, which includes parameterizations of lightning, corona from ground, ion production and capture, and inductive and noninductive electrification mechanisms, as well as advanced treatments of advection, microphysics, and dynamics. Our most recent improvements have been to improve the model's treatment of microphysics, particularly particle size distributions. This model has been used to simulate many types of storms, from small isolated storms to extensive storm systems, supercell storms, and an idealized hurricane, with excellent similitude to observed kinematic structure in many cases. We will show examples of our simulations and will discuss relationships among the model fields, particularly between lightning and other storm properties. Lightning usually is correlated with precipitation ice mass and with the mass flux through the mixed phase region for updrafts >10 m/s.

MacGorman, D., C. Ziegler, T. Mansell, J. Straka, P. Krehbiel, B. Rison, T. Hamlin, 2005: Applications of advanced lightning mapping technologies to storm research and weather operations. Preprints, Conference on Meteorological Applications of Lightning Data, San Diego, CA, USA, American Meteorological Society, 2.1.

MacGorman, D. R., W. D. Rust, C. L. Ziegler, T. J. Schuur, E. R. Mansell, M. I. Biggerstaff, J. M. Straka, E. C. Bruning, K. M. Kuhlman, N. R. Ramig, C. D. Payne, N. S. Biermann, P. R. Krehbiel, W. Rison, T. Hamlin, L. D. Carey, 2005: Lightning relative to storm structure, evolution, and microphysics in TELEX. Preprints, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, 10R.7.

Mansell, E. R., D. R. MacGorman, C. L. Ziegler, J. M. Straka, 2005: Charge structure in a simulated multicell thunderstorm. Journal of Geophysical Research, 110, .

A three-dimensional dynamic cloud model is used to investigate electrification of the full life cycle of an idealized continental multicell storm. Five laboratory-based parameterizations of noninductive graupel-ice charge separation are compared. Inductive (i.e., electric field-dependent) charge separation is tested for rebounding graupel-droplet collisions. Each noninductive graupel-ice parameterization is combined with variations in the effectiveness of inductive charging (off, moderate, and strong) and in the minimum ice crystal concentration (10 or 50/L). Small atmospheric ion processes such as hydrometeor attachment and point discharge at the ground are treated explicitly. Three of the noninductive schemes readily produced a normal polarity charge structure, consisting of a main negative charge region with an upper main positive charge region and a lower positive charge region. Negative polarity cloud-to-ground (CG) flashes occurred when the lower positive charge (LPC) region had sufficient charge density to cause high electric fields. Two of the three also produced one or more +CG flashes. The other two noninductive charging schemes, which are dependent on the graupel rime accretion rate, tended to produce an initially inverted polarity charge structure and +CG flashes. The model results suggest that inductive graupel-droplet charge separation could play a role in the development of lower charge regions. Noninductive charging, on the other hand, was also found to be capable of producing strong lower charge regions in the tests with a minimum ice crystal concentration of 50/L.

Mansell, T., C. Ziegler, D. MacGorman, 2006: A Lightning Data Assimilation Technique for Mesoscale Forecast Models. Preprints, 1st International Lightning Meteorology Conference, Tucson, AZ, USA, Vaisala, CD-ROM, N/A. [Available from Vaisala, Inc., Tucson Operations, 2705 E. Medina Rd., Tucson, AZ, USA, 85706.]

Lightning observations have been assimilated into the COAMPS mesoscale model for improvement of forecast initial conditions. Data are used from the National Lightning Detection Network (NLDN, cloud-to-ground lightning detection) and a Lightning Mapping Array (LMA; total lightning detection) that was installed in western Kansas/eastern Colorado. The assimilation method uses lightning as a proxy for the presence or absence of deep convection. During assimilation, lightning data are used to control the Kain-Fritsch (KF) convection parameterization scheme (CPS). The KF scheme can be forced to try to produce convection where lightning indicated storms, and, conversely, can optionally be prevented from producing spurious convection where no lightning was observed. Up to 1 g/kg of water vapor may be added to the boundary layer when the KF convection is too weak. The method does not make any use lightning-rainfall relationships, rather allowing the KF scheme to generate heating and cooling rates from its modeled convection. The method could therefore be used easily for real-time assimilation of any source of lightning observations.

Results will be presented for a warm-season test case 20-21 July 2000, when storms initiated and developed in large systems in Kansas both days. The second round of convection began by 22:00 UTC (20 July), and storm system with strong outflow had developed by 00 UTC on 21 July. Lightning data were assimilated over a 24 hour period (starting at 00 UTC on 20 July), covering the first round of convection and the start of the second. A control run was spun up over the same period only with the usual 12-hourly update cycle. As expected, during the assimilation period the model produces substantially more accurate precipitation (rates and location) than the control forecast. Even when water vapor was added to enhance convection, the rainfall rates were generally less than those indicated by rain gauge data. A forecast was started from the resulting initial condition at 00 UTC on 21 July 2000.

The lightning assimilation was successful in generating the cold pool that was present in the surface observations at initialization of the forecast. The resulting forecast showed considerably more skill than the control forecast, especially in the first few hours as convection was triggered by the propagation of the cold pool boundary.

Mansell, E. R., C. L. Ziegler, D. R. MacGorman, 2006: A Lightning Data Assimilation Technique for Mesoscale Forecast Models. Preprints, Second Conference on Meteorological Applications of Lightning Data, Atlanta, GA, USA, American Meteorological Society, 4.2.

Lightning observations have been assimilated into the COAMPS mesoscale model for improvement of forecast initial conditions. Data are used from the National Lightning Detection Network (NLDN, cloud-to-ground lightning detection) and a Lightning Mapping Array (LMA; total lightning detection) that was installed in western Kansas/eastern Colorado. The assimilation method uses lightning as a proxy for the presence or absence of deep convection. During assimilation, lightning data are used to control the Kain-Fritsch (KF) convection parameterization scheme (CPS). The KF scheme can be forced to try to produce convection where lightning indicated storms, and, conversely, can optionally be prevented from producing spurious convection where no lightning was observed. Up to 1 g/kg of water vapor may be added to the boundary layer when the KF convection is too weak. The method does not make any use lightning-rainfall relationships, rather allowing the KF scheme to generate heating and cooling rates from its modeled convection. The method could therefore be used easily for real-time assimilation of any source of lightning observations.

Results will be presented for a warm-season test case 20-21 July 2000, when storms initiated and developed in large systems in Kansas both days. The second round of convection began by 22:00 UTC (20 July), and storm system with strong outflow had developed by 00 UTC on 21 July. Lightning data were assimilated over a 24 hour period (starting at 00 UTC on 20 July), covering the first round of convection and the start of the second. A control run was spun up over the same period only with the usual 12-hourly update cycle. As expected, during the assimilation period the model produces substantially more accurate precipitation (rates and location) than the control forecast. Even when water vapor was added to enhance convection, the rainfall rates were generally less than those indicated by rain gauge data. A forecast was started from the resulting initial condition at 00 UTC on 21 July 2000.

The lightning assimilation was successful in generating the cold pool that was present in the surface observations at initialization of the forecast. The resulting forecast showed considerably more skill than the control forecast, especially in the first few hours as convection was triggered by the propagation of the cold pool boundary.

Available online at http://ams.confex.com/ams/Annual2006/techprogram/paper_104180.htm.

Mansell, E. R., C. L. Ziegler, D. R. MacGorman, 2007: A Lightning Data Assimilation Technique for Mesoscale Forecast Models. Monthly Weather Review, 135, 1732-1748.

Lightning observations have been assimilated into a mesoscale model for improvement of forecast initial conditions. Data are used from the National Lightning Detection Network (cloud-to-ground lightning detection) and a Lightning Mapping Array (total lightning detection) that was installed in western Kansas–eastern Colorado. The assimilation method uses lightning as a proxy for the presence or absence of deep convection. During assimilation, lightning data are used to control the Kain–Fritsch (KF) convection parameterization scheme. The KF scheme can be forced to try to produce convection where lightning indicated storms, and, conversely, can optionally be prevented from producing spurious convection where no lightning was observed. Up to 1 g/kg of water vapor may be added to the boundary layer when the KF convection is too weak. The method does not employ any lightning–rainfall relationships, but rather allows the KF scheme to generate heating and cooling rates from its modeled convection. The method could therefore easily be used for real-time assimilation of any source of lightning observations. For the case study, the lightning assimilation was successful in generating cold pools that were present in the surface observations at initialization of the forecast. The resulting forecast showed considerably more skill than the control forecast, especially in the first few hours as convection was triggered by the propagation of the cold pool boundary.

Mansell, E., C. L. Ziegler, E. Bruning, 2007: Simulated electrification of a TELEX multicell storm. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, International Commission on Atmospheric Electricity, 290-293.

Mansell, E. R., C. L. Ziegler, E. C. Bruning, 2010: Simulated electrification of a small thunderstorm with two-moment bulk microphysics. Journal of the Atmospheric Sciences, 67, 171-194.

Electrification and lightning are simulated for a small continental multicell storm. The results are consistent with observations and thus provide additional understanding of the charging processes and evolution of this storm. The first six observed lightning flashes were all negative cloud-to ground (CG) flashes, after which intracloud (IC) flashes also occurred between middle and upper levels of the storm. The model simulation reproduces the basic evolution of lightning from low and middle levels to upper levels. The observed lightning indicated an initial charge structure of at least an inverted dipole (negative charge above positive). The simulations show that noninductive charge separation higher in the storm can enhance the main negative charge sufficiently to produce negative CG flashes before upper level IC flashes commence. The result is a ‘‘bottom-heavy’’ tripole charge structure with midlevel negative charge and a lower positive charge region that is more significant than the upper positive region, in contrast to the traditional tripole structure that has a less significant lower positive charge region. Additionally, the occurrence of cloud-to-ground lightning is not necessarily a result of excess net charge carried by the storm, but it is primarily caused by the local potential imbalance between the lowest charge regions.

The two-moment microphysics scheme used for this study predicted mass mixing ratio and number concentration of cloud droplets, rain, ice crystals, snow, and graupel. Bulk particle density of graupel was also predicted, which allows a single category to represent a greater range of particle characteristics. (An additional hail category is available but was not needed for the present study.) The prediction of hydrometeor number concentration is particularly critical for charge separation at higher temperatures (-5 < T < -20 deg C) in the mixed phase region, where ice crystals are produced by rime fracturing (Hallett–Mossop process) and by splintering of freezing drops. Cloud droplet concentration prediction also affected the rates of inductive charge separation between graupel and droplets.

Available online at http://journals.ametsoc.org/doi/pdf/10.1175/2009JAS2965.1.

Mansell, E. R., C. L. Ziegler, 2011: CCN Effects on Simulated Storm Electrification and Precipitation. Extended Abstracts, 18th Conf. Planned and Inadvertent Weather Modification, Seattle, WA, USA, Amer. Met. Soc., J15.2.

The effects of concentration of cloud condensation nuclei (CCN) on cloud microphysics have long been recognized, but the resultant effects on storm electrification are relatively unexplored. In the present study, a high-resolution 3D model is employed with 2-moment microphysics (hydrometeor mass and number concentration) and electrification and lightning to simulate a storm observed in Oklahoma during the TELEX-2004 experiment (Mansell et al. 2010, J. Atmos. Sci.). CCN concentration is predicted as a single category monodisperse size spectrum approximating small aerosols. Graupel and hail particle densities are also predicted and are mainly determined by rime density. Rime density in turn is a function of droplet size (affected by CCN concentration) and impact speed. Graupel density is also used as a crude roughness parameter to scale the drag coefficient in the fall speed.

A range of CCN concentrations (50 to 15000 cm-3) were tested in a weak CAPE (Convective Available Potential Energy) environment (918 J/kg) that produced weakly multicell convection. Greater CCN concentration has the expected effects of shifting the initial formation of rain drops via collision-coalescence to later times and higher altitudes. Even at the highest CCN concentrations, however, vapor supply in the updraft remains sufficient for droplets eventually to grow large enough for coalescence to become appreciable before the appearance of graupel, so the warm-rain process is not completely shut down in this case. Peak updraft values increased modestly with increasing CCN from 16.8 m/s (50 cm-3) to 19.5 m/s (500 cm-3). Above CCN of 500 cm-3, peak updraft varied little from 19.5 m/s.

Time-integrated mass of graupel increases monotonically with increasing CCN up to about 2000-3 and decreases somewhat at higher CCN concentrations (Fig. 1). Time-integrated updraft volume generally increases with greater CCN concentrations, as well, but reached a plateau for CCN greater than 500 cm-3. Other effects of CCN concentration were variable. The simulated storms had maximum flash rates of 0 to 17 per minute and from 0 to 150 total flashes (Fig. 1). The most intense electrification (total lightning sources) was for CCN concentrations of 1000 to 3000 cm-3, dropping off toward lower and higher CCN values (Fig. 1; no flashes at 50-100 cm-3, and 3-4 total flashes for CCN >= 8000 cm-3.

Available online at http://ams.confex.com/ams/91Annual/webprogram/Paper180497.html.

Mansell, E. R., C. L. Ziegler, 2011: Aerosol (CCN) Effects on Simulated Storm Electrification and Precipitation. Preprints, 14th International Conference on Atmospheric Electricity, Rio de Janeiro, Brazil, International Commission on Atmospheric Electricity, CD-ROM, NA.

The effects of cloud condensation nuclei (CCN) concentrations strongly affected the microphysical and electrical evolution of a numerically simulated small storm. Graupel and lightning production increased monotonically as CCN increase from 50 cm-3 to about 2000 cm-3, where graupel production leveled off (up to 8000 cm-3 ). At higher CCN concentrations (>2000 cm-3 ), lightning activity either dropped dramatically (HM1) or remained steady (HM2), depending on the parameterization of Hallett-Mossop riming ice multiplication (HM1/HM2).

Marsh, P. T., H. E. Brooks, D. J. Karoly, 2007: Assessment of the severe weather environment in North America simulated by a global climate model. Atmospheric Science Letters, 8, 106.

Annual and seasonal cycles of convectively important atmospheric parameters for North America have been computed using the Community Climate System Model version 3 (CCSM3) Global Climate Model using a decade of CCSM3 data. Results for the spatial and temporal distributions of environments conducive to severe convective weather qualitatively agree with observational estimates from NCAR/NCEP global reanalyses, although the model underestimates the frequency of occurrence of severe weather environments. This result demonstrates the possibility for future studies aimed at determining possible changes in the distribution of severe weather environments associated with global climate change.

Marsh, P. T., H. E. Brooks, D. J. Karoly, 2009: Preliminary investigation into the severe thunderstorm environment of Europe simulated by the Community Climate System Model 3. Atmospheric Research, 93, 607-618.

Seasonal cycles of parameters conducive for the development of severe thunderstorms were computed using 20 years of output from the Community Climate System Model v3 (CCSM3) for both a 20th century simulation and a 21st century simulation. These parameters were compared against parameters calculated from the NCEP/NCAR Global Reanalysis data, which are of similar resolution. The CCSM3's current simulation produced seasonal and spatial distributions of both mean CAPE and favorable severe environments that were qualitatively similar to the NCEP/NCAR Global Reanalysis, although the CCSM3 underestimates the frequency of severe thunderstorm environments. Preliminary comparisons of the CCSM3's 21st century simulation under the IPCC's A2 emissions scenario to the 20th century simulation indicated a slight increase in mean CAPE in the cool season and a slight decrease in the warm season and little change in mean wind shear. However, there was a small increase in favorable severe environments for most locations resulting from an increase in the joint occurrence of high CAPE and high deep layer shear. Regions near the Mediterranean Sea experienced the biggest increase in both mean CAPE and favorable severe environments, regions near the Faeroe Islands experienced an increase in only seasonal mean CAPE, and regions across northern Europe experienced little change.

Marsh, P. T., J. S. Kain, S. J. Weiss, I. L. Jirak, R. A. Sobash, F. Kong, K. W. Thomas, M. Xue, 2010: INVESTIGATING A FUNDAMENTAL COMPONENT OF A WARN-ON FORECAST SYSTEM IN A COLLABORATIVE REAL-TIME EXPERIMENT. Extended Abstracts, 11th Severe Local Storms Conference, Denver, CO, USA, American Meteorological Society, 14.4.

The Warn-on-Forecast paradigm (WoF) envisions probabilistic prediction of severe convective phenomena based on ensemble forecasts using high-resolution models. One of many scientific challenges facing Warn-on-Forecast is how to construct reliable probabilistic information regarding severe convective phenomena when these phenomena will not be explicitly resolvable for many years to come. One approach to address this issue is to identify “extreme” model-generated features that have strong correlations with observed extreme convective phenomena, and then use the former as surrogates for the extreme phenomena in question. This “surrogate-severe” (SS) approach is fundamentally different from traditional applications of NWP for severe weather because it is phenomenon based. In particular, it relies on identification of explicit convective phenomena rather than environmental conditions to predict the likelihood of severe thunderstorms.

Sobash et al. (2009) established the viability of this approach using several different SS diagnostic quantities. Their work used a “neighborhood” approach based on the concepts in Theis et al. (2005) and Brooks et al. (1998) to produce severe-weather probability forecasts based on the locations of SS features in a deterministic model. In the current study, we extend the concepts developed by Sobash et al. (2009) to a 26-member storm-scale ensemble. This ensemble was produced by the Center for Analysis and Prediction of Storms (CAPS) during the 2010 NOAA HWT Spring Experiment. In the ensemble-based application it was found that interpretation of derived probabilistic forecasts depends strongly on the parameters used for post-processing. This presentation examines examples of various derived products, their potential utility for current Outlook-scale severe weather forecasts, and their possible application within the focused scales of WoF for severe weather.

References:
Brooks, H. E., M. Kay, and J. A. Hart, 1998: Objective limits on forecasting skill of rare events. Preprints, 19th Conference on Severe Local Storms, Minneapolis, Minnesota, Amer. Meteor. Soc., 552-555.

Sobash, R. A., J. S. Kain, D. R. Bright, A. R. Dean, M. C. Coniglio, S. J. Weiss, and J. J. Levit, 2009: Forecast guidance for severe thunderstorms based on identification of extreme phenomena in convection-allowing model forecasts. Preprints, 23rd Conference on Weather Analysis and Forecasting/19th Conference on Numerical Weather Prediction, Amer. Meteor. Soc., Omaha, NE. CD-ROM 4B.6

Theis, S. E., A. Hense, and U. Damrath, 2005: Probabilistic precipitation forecasts from a deterministic model: A pragmatic approach. Meteor. Appl., 12, 257–268.

Available online at http://ams.confex.com/ams/25SLS/techprogram/paper_176218.htm.

Marsh, P. T., J. S. Kain, V. Lakshmanan, A. J. Clark, N. M. Hitchens, J. Hardy, 2012: A Method for Calibrating Deterministic Forecasts of Rare Events. Weather and Forecasting, 27, 531-538.

Convection-allowing models offer forecasters unique insight into convective hazards relative to numerical models using parameterized convection. However, methods to best characterize the uncertainty of guidance derived from convection-allowing models are still unrefined. This paper proposes a method of deriving calibrated probabilistic forecasts of rare events from deterministic forecasts by fitting a parametric kernel density function to the model’s historical spatial error characteristics. This kernel density function is then applied to individual forecast fields to produce probabilistic forecasts.

Marsh, P. T., H. E. Brooks, 2012: Comments on “Tornado Risk Analysis: Is Dixie Alley an Extension of Tornado Alley?”. Bulletin of the American Meteorological Society, 93, 405-407.

McFarquhar, G. M., S. Ghan, J. Verlinde, A. Korolev, J. W. Strapp, B. Schmid, J. Tomlinson, M. Wolde, S. Brooks, D. Cziczo, M. Dubey, J. Fan, C. Flynn, I. Gultepe, J. Hubbe, M. Gilles, A. Laskin, P. Lawson, W. R. Leaitch, P. Liu, X. Liu, D. Lubin, C. Mazzoleni, A. M. Macdonald, R. Moffet, H. Morrison, M. Ovtchinnikov, M. D. Shupe, D. D. Turner, S. Xie, A. Zelenyuk, K. Bae, M. Freer, A. Glen, 2011: Indirect and semi-direct aerosol campaign (ISDAC): The impact of Arctic aerosols on clouds. Bulletin of the American Meteorological Society, 92, 183-201.

A comprehensive dataset of microphysical and radiative properties of aerosols and clouds in the arctic boundary layer in the vicinity of Barrow, Alaska was collected in April 2008 during the Indirect and Semi-Direct Aerosol Campaign (ISDAC) sponsored by the Department of Energy Atmospheric Radiation Measurement (ARM) and Atmospheric Science Programs. The primary aim of ISDAC was to examine effects of aerosols on clouds that contain both liquid and ice water for clean and polluted environments. ISDAC utilized the ARM permanent observational facilities at Barrow. These include a cloud radar, a polarized micropulse lidar, and an atmospheric emitted radiance interferometer as well as instruments specially deployed for ISDAC measuring aerosol, ice fog, precipitation and spectral shortwave radiation. The National Research Council of Canada Convair-580 flew 27 sorties during ISDAC, collecting data using an unprecedented 42 state-of-the-art cloud and aerosol instruments for more than 100 hours on 12 different days. Data were obtained on a number of days, including above, below and within single- layer stratus on 8 April and 26 April 2008. These data enable a process-oriented understanding of how aerosols affect the microphysical and radiative properties of arctic clouds influenced by different surface conditions and aerosol loads. Observations acquired on a heavily polluted day, 19 April 2008, are enhancing this understanding. Data acquired in cirrus on transit flights between Fairbanks and Barrow are improving our understanding of the performance of cloud probes in ice. Ultimately the ISDAC data will be used to improve the representation of cloud and aerosol processes in models covering a variety of spatial and temporal scales and pollution regimes, and to determine the extent to which long-term surface-based measurements can provide retrievals of aerosols, clouds, precipitation and radiative heating in the Arctic.

McLaughlin, D., D. Pepyne, B. Philips, J. Kurose, M. Zink, D. Westbrook, E. Lyons, E. Knapp, A. Hopf, A. Defonzo, R. Contreras, T. Djaferis, E. Insanic, S. Frasier, V. Chandrasekar, F. Junyent, N. Bharadwaj, Y. Wang, Y. Liu, B. Dolan, K. Droegemeier, J. Brotzge, M. Xue, K. Kloesel, K. Brewster, F. Carr, S. Cruz-Pol, K. Hondl, P. Kollias, 2009: Short-Wavelength Technology and the Potential For Distributed Networks of Small Radar Systems. Bulletin of the American Meteorological Society, 90, 1797-1817.

Dense networks of short-range radars capable of mapping storms and detecting atmospheric hazards are described. Composed of small X-band (9.4 GHz) radars spaced tens of kilometers apart, these networks defeat the Earth curvature blockage that limits today's long-range weather radars and enables observing capabilities fundamentally beyond the operational state-of-the-art radars. These capabilities include multiple Doppler observations for mapping horizontal wind vectors, subkilometer spatial resolution, and rapid-update (tens of seconds) observations extending from the boundary layer up to the tops of storms. The small physical size and low-power design of these radars permits the consideration of commercial electronic manufacturing approaches and radar installation on rooftops, communications towers, and other infrastructure elements, leading to cost-effective network deployments. The networks can be architected in such a way that the sampling strategy dynamically responds to changing weather to simultaneously accommodate the data needs of multiple types of end users. Such networks have the potential to supplement, or replace, the physically large long-range civil infrastructure radars in use today.

McPherson, R. A., D. J. Stensrud, 2005: Influences of a winter wheat belt on the evolution of the boundary layer. Monthly Weather Review, 133, 2178-2199.

Evidence exists that a large-scale alteration of land use by humans can cause changes in the climatology of the region. The largest-scale transformation is the substitution of native landscape by agricultural cropland. This modeling study examines the impact of a direct substitution of one type of grassland for another - in this case, the replacement of tallgrass prairie with winter wheat. The primary difference between these grasses is their growing season: native prairie grasses of the U. S. Great Plains are warm-season grasses whereas winter wheat is a cool-season grass.

Case study simulations were conducted for 27 March 2000 and 5 April 2000 - days analyzed in previous observational studies. The simulations provided additional insight into the physical processes involved and changes that occurred throughout the depth of the planetary boundary layer. Results indicate the following: 1) with the proper adjustment of vegetation parameters, land-use type, fractional vegetation coverage, and soil moisture, the numerical simulations were able to capture the overall patterns measured near the surface across a growing wheat belt during benign springtime conditions in Oklahoma; 2) the impacts of the mesoscale belt of growing wheat included increased values of latent heat flux and decreased values of sensible heat flux over the wheat, increased values of atmospheric moisture near the surface above and downstream of the wheat, and a shallower planetary boundary layer (PBL) above and downstream of the wheat; 3) in the sheared environments that were examined, a shallower PBL that resulted from growing wheat (rather than natural vegetation) led to reduced entrainment of higher momentum air into the PBL and, thus, weaker winds within the PBL over and downwind from the growing wheat; 4) for the cases studied, gradients in sensible heat were insufficient to establish an unambiguous vegetation breeze or its corresponding mesoscale circulation; 5) the initialization of soil moisture within the root zone aided latent heat fluxes from growing vegetation; and 6) reasonable specification of land surface parametes was required for the correct simulation and prediction of surface heat fluxes and resulting boundary layer development.

Mejia, J. F., M. Douglas, 2005: Mean structure and variability of the low-level jet across the central Gulf of California from NOAA WP-3D flight level observations during the North American Monsoon Experiment. Preprints, 6th Conference on Coastal Atmospheric and Oceanic Prediction and Processes (6COASTAL), San Diego, CA, USA, American Meteorological Society, CD-ROM, 5.8.

Mejia, J. F., M. W. Douglas, 2005: Mean structure and variability of the low-level jet across the central Gulf of California from NOAA WP-3D flight level observations during the North American Monsoon Experiment. Preprints, Sixth Conference on Coastal Atmospheric and Oceanic Prediction and Processes, San Diego, CA, USA, American Meteorological Society, 5.8.

This presentation describes lower tropospheric features over the Gulf of California, Mexico using NOAA WP-3D aircraft flight level observations made during July and August 2004 as part of the North American Monsoon Experiment (NAME). The WP-3D was flown to capture the 3-dimensional structure of the low level flow during both "strong" and "normal" monsoon flow conditions in this region. Ten flights were carried out during NAME; they were focused mainly on measuring moisture fluxes and the low-level jet (LLJ) flow along the Gulf of California. The low-level flow over the Gulf of California exhibits a low-level jet structure that is characteristic during the summertime and its stronger events appear to transport a significant amount of moisture into the southwestern United States and northwestern Mexico. We compare analyses produced by models (NCEP regional reanalysis) and the NAME sounding network observations to the aircraft measurements made on the flight days. From comparison of the aircraft data with the NAME sounding network observations we can determine how accurately the sounding network tends to estimate the actual moisture flux over the Gulf of California

Mejia, J. F., M. W. Douglas, 2005: Intensive “porpoising” with a research aircraft to determine atmospheric structure during the SALLJEX and NAME programs. Preprints, 13th Symposium on Meteorological Observations and Instrumentation, Savannah, GA, USA, American Meteorological Society, JP1.32.

Two recent field programs have focused on describing aspects of low-level jets in the Americas. Both programs have used NOAA WP-3D research aircraft to make mesoscale measurements about the jets, with the object of describing the 3-dimensional structure of the flow over relatively large areas. During both field programs the WP-3D was used as a probe, with the aircraft moving vertically while carrying out flight patterns that were mostly predetermined. The object was to describe both the horizontal structure of the jets while also describing the vertical variation of the flow. This involved trade-offs in the design of the flights. The SALLJEX flights sampled a deeper jet flow, necessitating greater vertical coverage and lesser horizontal resolution. The NAME flights were intended to sample a shallow jet that was confined in part by topography. This presentation summarizes the advantages and disadvantages of using the aircraft in a porpoising mode, with examples drawn from both experiments. The objective is to explain the benefits (and limitations) of the porpoising procedure and discuss how it may be employed most effectively.

Melnikov, V., R. J. Doviak, D. S. Zrnic, D. J. Stensrud, 2011: Mapping Bragg Scatter with a Polarimetric WSR-88D. Journal of Atmospheric and Oceanic Technology, 28, 1273-1285.

Using a polarimetric Weather Surveillance Radar-1988 Doppler (WSR-88D) radar to distinguish Bragg scatterers from insects and birds in an optically clear atmosphere has the potential to provide information on convective boundary layer depth. Measured median differential reflectivities ZDR of Bragg scatterers lie between −0.08 and 0.06 dB, which supports the hypothesis that the intrinsic ZDR of Bragg scatters is 0 dB. Thus, the intrinsic 0 dB of Bragg scatter can be used for verifying of ZDR radar calibration. If insects and birds are spatially separated from Bragg scatterers, the dual-polarization capability of the WSR-88D allows distinguishing echoes from these two types of scatterers since ZDR from biota is significantly larger than 0 dB. In mixtures of Bragg and biota scatter, polarimetric spectral analysis shows differences in portions of the H and V spectra where birds and insects could be contaminating echoes from Bragg scatterers. Enhancements to data collection and signal processing allow power measurement, with a standard deviation of about 1 dB, of weak echoes from Bragg scatterers having equivalent reflectivity factors of about −28 dBZ at distance of 10 km from the radar. This level of reflectivity corresponds to a refractive index structure parameter of about 4 × 10^(−15) m^(−2/3), a typical magnitude found in maritime air.

Melnikov, V., R. J. Doviak, D. S. Zrnic, D. J. Stensrud, 2011: Fine structures of refractivity in the boundary layer revealed with a polarimetric WSR-88D. Extended Abstracts, 35-th Conference on Radar Meteorology, Pittsburgh, PA, USA, AMS, 191078.

Types of radar Bragg scatter in clear air.

Available online at http://ams.confex.com/ams/35Radar/webprogram/Paper191078.html.

Morss, R. E., J. K. Lazo, B. G. Brown, H. E. Brooks, P. T. Ganderton, B. N. Mills, 2008: Societal and Economic Research and Applications For Weather Forecasts: Priorities for the North American THORPEX Program. Bulletin of the American Meteorological Society, 89, 335-346.

Despite the meteorological community's long-term interest in weather–society interactions, efforts to understand socioeconomic aspects of weather prediction and to incorporate this knowledge into the weather prediction system have yet to reach critical mass. This article aims to reinvigorate interest in societal and economic research and applications (SERA) activities within the meteorological and social science communities by exploring key SERA issues and proposing SERA priorities for the next decade.

The priorities were developed by the authors, building on previous work, with input from a diverse group of social scientists and meteorologists who participated in a SERA workshop in August 2006. The workshop was organized to provide input to the North American regional component of THORPEX: A Global Atmospheric Research Programme, but the priorities identified are broadly applicable to all weather forecast research and applications.

To motivate and frame SERA activities, we first discuss the concept of high-impact weather forecasts and the chain from forecast creation to value realization. Next, we present five interconnected SERA priority themes—use of forecast information in decision making, communication of forecast uncertainty, user-relevant verification, economic value of forecasts, and decision support—and propose research integrated across the themes.

SERA activities can significantly improve understanding of weather–society interactions to the benefit of the meteorological community and society. However, reaching this potential will require dedicated effort to bring together and maintain a sustainable interdisciplinary community.

Murillo, J., M. W. Douglas, R. Orozco, J. M. Galvez, J. F. Mejia, C. Brown, 2005: Quality control of pilot balloon data for climate monitoring. Preprints, 13th Symposium on Meteorological Observations and Instrumentation, Savannah, GA, USA, American Meteorological Society, JP1.30.

Ortega, K. L., P. T. Marsh, K. A. Scharfenberg, K. L. Manross, 2011: Populations at risk: Estimating the number of people in the path of 27 April 2011. Preprints, 36th Annual Meeting of the National Weather Association, Birmingham, AL, USA, National Weather Association, P1.27.

Tornado outbreaks can be evaluated in numerous ways. Typically, an outbreak is ranked by number of tornadoes, strength of the tornadoes, the number of fatalities or some combination. Warning effectiveness is usually implied through traditional POD/FAR measures and by the number of injuries or fatalities.

We will investigate using gridded population data to estimate the populations affected by tornadoes and warnings. Population estimates could help in ranking and evaluating not only the outbreak itself, but also warning effectiveness.

Park, H., A. Ryzhkov, H. Reeves, T. Schuur, 2009: Classification of precipitation types during transitional winter weather using the RUC model and polarimetric radar retrievals. Extended Abstracts, 34th Conference on Radar Meteorology, Williamsburg, VA, USA, AMS, P2.20.

Available online at http://ams.confex.com/ams/pdfpapers/155580.pdf.

Parker, D. J., M. W. Douglas, M. Christoph, A. H. Fink, S. Janicot, J. B. Ngamini, E. Afiesimama, A. Agusti-Panareda, A. Beljaars, F. Dide, A. Ddiedhiou, T. Lebel, J. Polcher, J. L. Redelsperger, C. Thorncroft, G. Wilson, 2008: The Amma radiosonde programme and its implications for the future of atmospheric monitoring over Africa.. Preprints, 28th Conference on Hurricanes and Tropical Meteorology, Orlando, FL, USA, American Meteorological Society, 3C.1.

This presentation describes the upper air observational programme which is being carried out as part of the African Monsoon Multidisciplinary Analysis (AMMA). An important goal of AMMA is to evaluate the impact of the upper-air data on weather and climate prediction for West Africa, and for the hurricane genesis regions of the tropical Atlantic. Since 2004, AMMA scientists have been working with operational agencies in Africa to reactivate silent radiosonde stations, to renovate unreliable stations, and to install new stations in regions of particular climatic importance. A comprehensive upper air network of 21 stations, including four GCOS Upper Air Network (GUAN) stations, is now active over West Africa, and during the AMMA Special Observing Period (SOP) June to September 2006 some 7000 soundings were made in the region, representing the greatest density of upper air observations ever since in the region, exceeding even the number of soundings made during the GATE programme of 1974. AMMA also encompassed a short, intensive campaign on a network of PILOT stations in the western part of the region, centered on Senegal. This activity both exposed the dilapidated state of the operational PILOT network in the region, and demonstrated that important upper air data can be collected at relatively low cost through PILOT soundings. Many operational lessons were learned in AMMA, involving technical problems in the harsh environment of sub-Saharan Africa and issues of funding, coordination and communication among the many nations and agencies involved. From these lessons we are able to make firm recommendations for the maintenance and operation of a useful upper air network in WMO Region I in the future.

Parker, D. J., A. Fink, S. Janicot, J. Ngamini, M. W. Douglas, E. Afiesimama, A. Agusti-Panareda, A. Beljaars, F. Dide, A. Diedhiou, T. Lebel, J. Polcher, J. L. Redelsperger, C. Thorncroft, G. A. Wilson, 2008: The Amma Radiosonde Program and its Implications for the Future of Atmospheric Monitoring Over Africa. Bulletin of the American Meteorological Society, 89, 1015-1027.

This article describes the upper-air program, which has been conducted as part of the African Monsoon Multidisciplinary Analysis (AMMA). Since 2004, AMMA scientists have been working in partnership with operational agencies in Africa to reactivate silent radiosonde stations, to renovate unreliable stations, and to install new stations in regions of particular climatic importance. A comprehensive upper-air network is now active over West Africa and has contributed to high-quality atmospheric monitoring over three monsoon seasons. During the period June to September 2006 high-frequency soundings were performed, in conjunction with intensive aircraft and ground-based activities: some 7,000 soundings were made, representing the greatest density of upper air measurements ever collected over the region. An important goal of AMMA is to evaluate the impact of these data on weather and climate prediction for West Africa, and for the hurricane genesis regions of the tropical Atlantic. Many operational difficulties were encountered in the program, involving technical problems in the harsh environment of sub-Saharan Africa and issues of funding, coordination, and communication among the many nations and agencies involved. In facing up to these difficulties, AMMA achieved a steady improvement in the number of soundings received by numerical weather prediction centers, with a success rate of over 88% by August 2007. From the experience of AMMA, we are therefore able to make firm recommendations for the maintenance and operation of a useful upper-air network in WMO Region I in the future.

Pinto, J., C. Kessinger, B. Hendrickson, D. Megenhardt, P. Harasti, Q. Xu, P. Zhang, Q. Zhao, M. Frost, J. Cook, S. Potts, 2007: Storm characterization and short term forecasting potential using a phase array radar. Extended Abstracts, 33rd Conference on Radar Meteorology, Cairns, Australia, Amer. Meteor. Soc., P5.18.

Available online at http://ams.confex.com/ams/pdfpapers/123703.pdf.

Potvin, C. K., A. Shapiro, M. Xue, 2012: Impact of a Vertical Vorticity Constraint in Variational Dual-Doppler Wind Analysis: Tests with Real and Simulated Supercell Data. Journal of Atmospheric and Oceanic Technology, 29, 32-49.

One of the greatest challenges to dual-Doppler retrieval of the vertical wind is the lack of low-level divergence information available to the mass conservation constraint. This study examines the impact of a vertical vorticity equation constraint on vertical velocity retrievals when radar observations are lacking near the ground. The analysis proceeds in a three-dimensional variational data assimilation (3DVAR) framework with the anelastic form of the vertical vorticity equation imposed along with traditional data, mass conservation, and smoothness constraints. The technique is tested using emulated radial wind observations of a supercell storm simulated by the Advanced Regional Prediction System (ARPS), as well as real dual-Doppler observations of a supercell storm that occurred in Oklahoma on 8 May 2003. Special attention is given to procedures to evaluate the vorticity tendency term, including spatially variable advection correction and estimation of the intrinsic evolution. Volume scan times ranging from 5 min, typical of operational radar networks, down to 30 s, achievable by rapid-scan mobile radars, are considered. The vorticity constraint substantially improves the vertical velocity retrievals in our experiments, particularly for volume scan times smaller than 2 min.

Qiu, C., A. Shao, S. Liu, Q. Xu, 2005: A two-step variational method for three-dimensional wind retrieval from single Doppler radar. Meteorology and Atmospheric Physics, 90(1-2), .

Qiu, C., A. Shao, Q. Xu, L. Wei, 2007: An Ensemble-Based 4DVar Approach Based on SVD Technique. Extended Abstracts, 18th Conference on Numerical Weather Prediction, park City, UT, USA, Amer. Meteor. Soc., P2.2.

Available online at http://ams.confex.com/ams/22WAF18NWP/techprogram/paper_123933.htm.

Qiu, C., A. Shao, Q. Xu, L. Wei, 2007: Fitting model fields to observations by using singular value decomposition – An ensemble-based 4DVar approach. Journal of Geophysical Research - D: Atmospheres., 112, .

Rauhala, J., H. E. Brooks, D. M. Schultz, 2012: Tornado Climatology of Finland. Monthly Weather Review, 140, 1446-1456.

A tornado climatology for Finland is constructed from 1796 to 2007. The climatology consists of two datasets. A historical dataset (1796-1996) is largely constructed from newspaper archives and other historical archives and datasets, and a recent dataset (1997-2007) is largely constructed from eyewitness accounts sent to the Finnish Meteorological Institute and news reports. This article describes the process of collecting and evaluating possible tornado reports. Altogether, 298 Finnish tornado cases comprise the climatology: 129 from the historical dataset and 169 from the recent dataset. An annual average of 14 tornado cases occur in Finland (1997-2007).
A case with a significant tornado (F2 or stronger) occurs in our database on average every other year, comprising 14% of all tornado cases. All documented tornadoes in Finland have occurred between April and November. As in the neighbouring countries in northern Europe, July and August are the months with the maximum frequency of tornado cases, coincident with the highest lightning occurrence both over land and sea. Waterspouts tend to be favored later in the summer, peaking in August. The peak month for significant tornadoes is August. The diurnal peak for tornado cases is 1700-1859 local time.

Reeves, H. D., R. Rotunno, 2008: Orographic Flow Response to Variations in Upstream Humidity. Journal of the Atmospheric Sciences, 65, 3557-3570.

The effects of upstream relative humidity, RH , on low-level wind and precipitation patterns for low-speed, statically stable flows over a mountain are investigated using idealized two- and three-dimensional numerical-simulation experiments wherein RH is increased from 0 to 100%. For RH less than some critical threshold, the flow upstream becomes less decelerated as RH is increased; for RH greater than this threshold, the flow upstream becomes more decelerated as RH is increased. This increasing deceleration with RH is due to locally enhanced static stability owing to enhanced condensation near the freezing level. Analyses from the simulations indicate that the lifted condensation level and the height of the freezing level are significant control parameters for the upstream-flow deceleration in the steady-state solutions. Dimensional analysis using these control parameters (as well as others) brings forth new nondimensional parameters that are shown to enter into analytic formulas for the orographic upstream-flow deceleration in a moist atmosphere.

Reeves, H. D., D. J. Stensrud, 2009: Synoptic-scale flow and valley cold pool evolution in the Western United States. Weather and Forecasting, 24, 1625-1643.

Valley cold pools (VCPs), which are trapped, cold layers of air at the bottoms of basins or valleys, pose a significant problem for forecasters because they can lead to several forms of difficult-to-forecast and hazardous weather such as fog, freezing rain, or poor air quality. Numerical models have historically failed to routinely provide accurate guidance on the formation and demise of VCPs, making the forecast problem more challenging. In some case studies of persistent wintertime VCPs, there is a connection between the movement of upper-level waves and the timing of VCP formation and decay. Herein, a 3-yr climatology of persistent wintertime VCPs for five valleys and basins in the western United States is performed to see how often VCP formation and decay coincides with synoptic-scale (~200-2000 km) wave motions. Valley cold pools are found to form most frequently as an upper-level ridge approaches the western United States and in response to strong midlevel warming. The VCPs usually last as long as the ridge is over the area and usually only end when a trough, and its associated midlevel cooling, move over the western United States. In fact, VCP strength appears to be almost entirely dictated by midlevel temperature changes, which suggests large-scale forcing is dominant for this type of VCP most of the time.

Reeves, H. D., K. L. Elmore, G. S. Manikin, D. J. Stensrud, 2011: Assessment of forecasts during persistent valley cold pools in the Bonneville Basin by the North American Mesoscale model. Weather and Forecasting, 26, 447-467.

The North American Mesoscale (NAM) model forecasts of low-level temperature and dewpoint during persistent valley cold pools in the Bonneville Basin of Utah are assessed. Stations near the east sidewall have a daytime cold and nighttime warm bias. This is due to a poor representation of the steep slopes on this side of the basin. Basin stations where the terrain is better represented by the model have a distinct warm, moist bias at night.
Stations in snow-covered areas have a cold bias for both day and night. Biases are not dependent on forecast lead or validation time. Several potential causes for the various errors are considered in a series of sensitivity experiments. An experiment with 4-km grid spacing, which better resolves the gradient of the slopes on the east side of the basin, yields smaller
errors along the east corridor of the basin. The NAM model assumes all soil water freezes at a temperature of 273 K. This is likely not representative of the freezing temperature in the salt flats in the western part of the basin, since salt reduces the freezing point of water. An experiment testing this hypothesis shows that reducing the freezing point of soil water in the salt flats leads to an average error reduction between 1.5 and 4 K, depending on the station and time of day. Using a planetary boundary layer scheme that has greater mixing alleviates the cold bias over snow somewhat, but the exact source of this bias could not be determined.

Reeves, H. D., K. L. Elmore, G. S. Manikin, D. J. Stensrud, 2011: Assessment of forecasts during persistent valley cold pools in the Bonneville basin by the North American Mesoscale Model.. Weather and Forecasting, 26, 447-467.

North American Mesoscale Model (NAM) forecasts of low-level temperature and dewpoint during persistent valley cold pools in the Bonneville Basin of Utah are assessed. Stations near the east sidewall have a daytime cold and nighttime warm bias. This is due to a poor representation of the steep slopes on this side of the basin. Basin stations where the terrain is better represented by the model have a distinct warm, moist bias at night. Stations in snow-covered areas have a cold bias for both day and night. Biases are not dependent on forecast lead or validation time. Several potential causes for the various errors are considered in a series of sensitivity experiments. An experiment with 4-km grid spacing, which better resolves the gradient of the slopes on the east side of the basin, yields smaller errors along the east corridor of the basin. The NAM assumes all soil water freezes at a temperature of 273 K. This is likely not representative of the freezing temperature in the salt flats in the western part of the basin, since salt reduces the freezing point of water. An experiment testing this hypothesis shows that reducing the freezing point of soil water in the salt flats leads to an average error reduction between 1.5 and 4 K, depending on the station and time of day. Using a planetary boundary layer scheme that has greater mixing alleviates the cold bias over snow somewhat, but the exact source of this bias could not be determined.

Scharfenberg, K. A., D. L. Andra, P. T. Marsh, K. L. Ortega, J. Brotzge, 2010: Tornado warning services for misoscale circulations in quasilinear convective systems. Extended Abstracts, 11th Severe Local Storms Conference, Denver, CO, USA, American Meteorological Society, P4.5.

Although long known to exist, misoscale circulations in quasilinear convective systems are becoming more readily observable in warning environments due to the improved availability of real-time radar data at higher spatial and temporal resolutions. These circulations are frequently associated with narrow paths of enhanced wind damage, particularly when combined with a fast system motion.

Some of these circulations have been observed to grow in size and/or intensity, and some last longer than others. It is a significant challenge to anticipate in real-time where circulations might develop along the line, which nascent circulations might intensify enough to produce swaths of enhanced wind damage, and which circulations will quickly dissipate.

In a storm environment capable of producing significant misoscale circulations, this presents a major dilemma regarding Tornado Warning services. Large, long duration Tornado Warnings to cover all possible tornadic circulations in a quasilinear system have potentially negative societal implications, setting into motion widespread protective and emergency response actions for, at the most, very isolated impacts. On the other hand, while a few of these circulations might intensify enough to be classified as tornadoes, by the time one is detected and a warning disseminated, the threat is usually over.

This presentation will show archived examples of misoscale circulations in quasilinear convective systems of various sizes, durations, and intensities, to illustrate the wide range of events observed. The discussion will focus on the difficulty in classifying these events as tornadic vs. non-tornadic, the challenge in anticipating transient tornadic circulations among the many weaker circulations, and the dilemma facing forecasters when deciding whether to issue a Tornado Warning during these events. The presentation will conclude with recommendations for effective warning services during such events.

Available online at http://ams.confex.com/ams/25SLS/techprogram/paper_176213.htm.

Schenkman, A. D., M. Xue, A. Shapiro, K. Brewster, J. Gao, 2011: The Analysis and Prediction of the 8–9 May 2007 Oklahoma Tornadic Mesoscale Convective System by Assimilating WSR-88D and CASA Radar Data Using 3DVAR. Monthly Weather Review, 139, 224-246.

The Advanced Regional Prediction System (ARPS) model is employed to perform high-resolution numerical simulations of a mesoscale convective system and associated cyclonic line-end vortex (LEV) that spawned several tornadoes in central Oklahoma on 8–9 May 2007. The simulation uses a 1000 km × 1000 km domain with 2-km horizontal grid spacing. The ARPS three-dimensional variational data assimilation (3DVAR) is used to assimilate a variety of data types. All experiments assimilate routine surface and upper-air observations as well as wind profiler and Oklahoma Mesonet data over a 1-h assimilation window. A subset of experiments assimilates radar data. Cloud and hydrometeor fields as well as in-cloud temperature are adjusted based on radar reflectivity data through the ARPS complex cloud analysis procedure. Radar data are assimilated from the Weather Surveillance Radar-1988 Doppler (WSR-88D) network as well as from the Engineering Research Center for Collaborative and Adaptive Sensing of the Atmosphere (CASA) network of four X-band Doppler radars. Three-hour forecasts are launched at the end of the assimilation window. The structure and evolution of the forecast MCS and LEV are markedly better throughout the forecast period in experiments in which radar data are assimilated. The assimilation of CASA radar data in addition to WSR-88D data increases the structural detail of the modeled squall line and MCS at the end of the assimilation window, which appears to yield a slightly better forecast track of the LEV.

Schenkman, A. D., M. Xue, A. Shapiro, K. Brewster, J. Gao, 2011: Impact of CASA Radar and Oklahoma Mesonet Data Assimilation on the Analysis and Prediction of Tornadic Mesovortices in an MCS. Monthly Weather Review, 139, 3422-3445.

The impact of radar and Oklahoma Mesonet data assimilation on the prediction of mesovortices in a tornadic mesoscale convective system (MCS) is examined. The radar data come from the operational Weather Surveillance Radar-1988 Doppler (WSR-88D) and the Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere’s (CASA) IP-1 radar network. The Advanced Regional Prediction System (ARPS) model is employed to perform high-resolution predictions of an MCS and the associated cyclonic line-end vortex that spawned several tornadoes in central Oklahoman 8–9 May 2007, while the ARPS three-dimensional variational data assimilation (3DVAR) system in combination with a complex cloud analysis package is used for the data analysis. A set of data assimilation and prediction experiments are performed on a 400-m resolution grid nested inside a 2-km grid, to examine the impact of radar data on the prediction of meso-g-scale vortices (mesovortices). An 80-min assimilation window is used in radar data assimilation experiments. An additional set of experiments examines the impact of assimilating 5-min data from the Oklahoma Mesonet in addition to the radar data. Qualitative comparison with observations shows highly accurate forecasts of mesovortices up to 80 min in advance of their genesis are obtained when the low-level shear in advance of the gust front is effectively analyzed. Accurate analysis of the low-level shear profile relies on assimilating high resolution low-level wind information. The most accurate analysis (and resulting prediction) is obtained in experiments that assimilate low-level radial velocity data from the CASA radars. Assimilation of 5-min observations from the Oklahoma Mesonet has a substantial positive impact on the analysis and forecast when high-resolution low-level wind observations from CASA are absent; when the low-level CASA wind data are assimilated, the impact of Mesonet data is smaller. Experiments that do not assimilate low-level wind data from CASA radars are unable to accurately resolve the low-level shear profile and gust front structure, precluding accurate prediction of mesovortex development.

Available online at http://journals.ametsoc.org/toc/mwre/139/11.

Schuur, T. J., H. S. Park, A. V. Ryzhkov, H. D. Reeves, 2012: Classification of precipitation types during transitional winter weather using the RUC model and polarimetric radar retrievals. Journal of Applied Meteorology and Climatology, 51, 763-779.

A new hydrometeor classification algorithm that combines thermodynamic output from the Rapid Update Cycle (RUC) model with polarimetric radar observations is introduced. The algorithm improves upon existing classification techniques that rely solely on polarimetric radar observations by using thermodynamic information to help to diagnose microphysical processes (such as melting or refreezing) that might occur aloft. This added information is especially important for transitional weather events for which past studies have shown radar-only techniques to be deficient. The algorithm first uses vertical profiles of wet-bulb temperature derived from the RUC model output to provide a background precipitation classification type. According to a set of empirical rules, polarimetric radar data are then used to refine precipitation-type categories when the observations are found to be inconsistent with the background classification. Using data from the polarimetric KOUN Weather Surveillance Radar-1988 Doppler (WSR-88D) located in Norman, Oklahoma, the algorithm is tested on a transitional winter-storm event that produced a combination of rain, freezing rain, ice pellets, and snow as it passed over central Oklahoma on 30 November 2006. Examples are presented in which the presence of a radar bright band (suggesting an elevated warm layer) is observed immediately above a background classification of dry snow (suggesting the absence of an elevated warm layer in the model output). Overall, the results demonstrate the potential benefits of combining polarimetric radar data with thermodynamic information from numerical models, with model output providing widespread coverage and polarimetric radar data providing an observation-based modification of the derived precipitation type at closer ranges.

Schwartz, C. S., J. S. Kain, S. J. Weiss, M. Xue, D. R. Bright, F. Kong, K. W. Thomas, J. J. Levit, M. C. Coniglio, 2009: Next-day convection-allowing WRF model guidance: A second look at 2 vs. 4 km grid spacing. Monthly Weather Review, 137, 3351-3372.

During the 2007 NOAA Hazardous Weather Testbed (HWT) Spring Experiment, the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma produced convection-allowing forecasts from a single deterministic 2 km model and a 10-member 4 km resolution ensemble. In this study, the 2 km deterministic output was compared with forecasts from the 4 km ensemble control member. Other than the difference in horizontal resolution, the two sets of forecasts featured identical WRFARW configurations, including vertical resolution, forecast domain, initial and lateral boundary conditions, and physical parameterizations. Therefore, forecast disparities were attributed solely to differences in horizontal grid spacing.

This study is a follow-up to similar work that was based on results from the 2005 Spring Experiment. Unlike the 2005 Experiment, however, model configurations were more rigorously controlled in the present study, providing a more robust dataset and a cleaner isolation of the dependence on horizontal resolution. Additionally, in this study, the 2 and 4 km output were compared to 12 km forecasts from the North American Mesoscale (NAM) model.

Model forecasts were analyzed using objective verification of mean hourly precipitation and visual comparison of individual events, primarily during the 21- to 33-hour forecast period to examine the utility of the models as next-day guidance. On average, both the 2 and 4 km model forecasts showed substantial improvement over the 12 km NAM. However, although the 2 km forecasts produced more detailed structures on the smallest resolvable scales, the patterns of convective initiation, evolution, and organization were remarkably similar to the 4 km output. Moreover, on average, metrics such as equitable threat score, frequency bias, and fractions skill score revealed no statistical improvement of the 2 km forecasts compared to the 4 km forecasts. These results, based on the 2007 dataset, corroborate previous findings, suggesting that decreasing horizontal grid spacing from 4 to 2 km provides little added value as next-day guidance for severe convective storm and heavy rain forecasters in the United States.

Schwartz, C. S., J. S. Kain, S. J. Weiss, D. R. Bright, M. Xue, F. Kong, K. W. Thomas, J. J. Levit, M. C. Coniglio, 2008: Next-day convection-allowing WRF model guidance: A second look at 2- vs. 4-km grid spacing. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., CD-ROM, P10.3. [Available from Jack Kain, NSSL, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Available online at http://ams.confex.com/ams/24SLS/techprogram/paper_142052.htm.

Schwartz, C. S., J. S. Kain, D. R. Bright, S. J. Weiss, M. Xue, F. Kong, J. J. Levit, M. C. Coniglio, M. S. Wandishin, 2008: Toward improved convection-allowing ensembles: Model physics sensitivities and optimizing probabilistic guidance with small ensemble membership. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., CD-ROM, 13A.6. [Available from Jack Kain, NSSL, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Available online at http://ams.confex.com/ams/24SLS/techprogram/paper_142048.htm.

Schwartz, C. S., J. S. Kain, D. R. Bright, S. J. Weiss, M. Xue, F. Kong, J. J. Levit, M. C. Coniglio, M. S. Wandishin, 2009: Optimizing probabilistic high resolution ensemble guidance for hydrologic prediction. Preprints, 23rd Conference on Hydrology, Phoenix, AZ, USA, Amer. Meteor. Soc., CD-ROM, 9.4.

Available online at http://ams.confex.com/ams/89annual/techprogram/paper_147171.htm.

Schwartz, C. S., J. S. Kain, M. C. Coniglio, S. J. Weiss, D. R. Bright, M. Xue, F. Kong, K. W. Thomas, M. S. Wandishin, 2010: Toward Improved Convection-Allowing Ensembles: Model Physics Sensitivities and Optimizing Probabilistic Guidance with Small Ensemble Membership. Weather and Forecasting, 25, 263-280.

During the 2007 NOAA Hazardous Weather Testbed Spring Experiment, the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma produced a daily 10-member 4-km horizontal resolution ensemble forecast covering approximately three-fourths of the continental United States. Each member used the Advanced Research version of the Weather Research and Forecasting (WRF-ARW) model core, which was initialized at 2100 UTC, ran for 33 h, and resolved convection explicitly. Different initial condition (IC), lateral boundary condition (LBC), and physics perturbations were introduced in 4 of the 10 ensemble members, while the remaining 6 members used identical ICs and LBCs, differing only in terms of microphysics (MP) and planetary boundary layer (PBL) parameterizations. This study focuses on precipitation forecasts from the ensemble.

The ensemble forecasts reveal WRF-ARW sensitivity to MP and PBL schemes. For example, over the 7-week experiment, the Mellor–Yamada–Janjić PBL and Ferrier MP parameterizations were associated with relatively high precipitation totals, while members configured with the Thompson MP or Yonsei University PBL scheme produced comparatively less precipitation. Additionally, different approaches for generating probabilistic ensemble guidance are explored. Specifically, a “neighborhood” approach is described and shown to considerably enhance the skill of probabilistic forecasts for precipitation when combined with a traditional technique of producing ensemble probability fields.

Segele, Z. T., D. J. Stensrud, I. C. Ratcliffe, G. M. Henebry, 2005: Influence of a hailstreak on boundary layer evolution. Monthly Weather Review, 133, 942-960.

Severe thunderstorms developed on 20 June 1997 and produced heavy precipitation, damaging winds, and large hail over two swaths in southeastern South Dakota. Calculations of fractional vegetation coverage (scaled from 0 to 1) based upon composite satellite data indicate that, within the hailstreak region, vegetation coverage decreased from 0.50 to near 0.25 owing to the damaging effects of hail on the growing vegetation. The northern edge of the larger hailstreak was located a few km south of Chamberlain, South Dakota, a National Weather Service surface observation site. Hourly observations from Chamberlain and several nearby surface sites in South Dakota are averaged over 7 days both before and after this hail event. These observations illustrate that the late afternoon (nighttime) temperatures are 2°C higher (2°C lower) near the hailstreak after the event than before the event. Similarly, daily average dewpoint temperatures after the event are 2.6°C lower near the hailstreak. These changes are consistent with the influences of a recently devegetated zone on changes to the surface energy budget.

To explore how these hailstreaks further affected the evolution of the planetary boundary layer in this region, two model simulations are performed using the Fifth-Generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model (MM5). In the control run, climatology is used for the land surface characteristics and hence the simulation is independent of the hailstreaks. In the hailstreak simulation (HSS), the fractional vegetation coverage and soil moisture in the hailstreak regions are modified to reflect the likely conditions within the hailstreaks. Two different days are simulated, one with low surface wind speeds and one with stronger surface wind speeds. For the low surface wind speed case, the HSS simulation produces a sea-breeze-like circulation in the boundary layer by mid-morning. For the stronger surface wind speed case, this sea-breeze-like circulation does not develop in the HSS, but the simulated low-level temperatures are modified over a larger area. These results suggest that to capture and reasonably simulate the evolution of boundary layer structures, there is a need for routine daily updates of land surface information. Hailstreaks also are important to consider in the future as the focus for observational studies on non-classical mesoscale circulations.

Shao, A., S. Xi, C. Qiu, Q. Xu, 2009: A hybrid-space approach for ensemble-based 4DVar. Journal of Geophysical Research - D: Atmospheres, 114, .

A new scheme is developed to improve the ensemble-based 4D variational data assimilation (En4DVar). In this scheme, leading singular vectors are extracted from 4D ensemble perturbations in a hybrid space and then used to construct the analysis increment to fit the 4D innovation (observation minus background) data. The hybrid space combines the 4D observation space with only a gridded 3D subspace at the end of each assimilation cycle, so its dimension can be much smaller than the dimension of the fully gridded 4D space used in the original En4DVar. This improves the computational efficiency. With this hybrid-space approach, the analysis increment can fit the 4D innovation data in the observation space directly and also provide the necessary initial condition in the gridded 3D subspace exclusively for the model integration into the next assimilation cycle, so the background covariance matrix can be and only needs to be constructed by the ensemble perturbations in the 3D subspace. This reduces the rank deficiency of the ensemble-constructed covariance matrix and improves analysis accuracy as long as the observations are not too sparse. The potential merits of the new scheme are demonstrated by assimilation experiments performed with an imperfect shallow-water equation model and simulated observations.

Smith, T. S., K. M. Kulman, K. L. Ortega, K. L. Manross, D. W. Burgess, J. Gao, D. J. Stensrud, 2010: A survey of real-time 3DVAR analyses conducted durng the 2010 Experimental Warning Program spring experiment. Extended Abstracts, 25th Conference on Severe Local Storms, Denver, CO, USA, AMS, P5.7.

Sobash, R. A., D. R. Bright, A. R. Dean, J. S. Kain, M. C. Coniglio, S. J. Weiss, J. J. Levit, 2008: Severe storm forecast guidance based on explicit identification of convective phenomena in WRF-model forecasts. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., CD-ROM, 11.3.

Available online at http://ams.confex.com/ams/24SLS/techprogram/paper_142187.htm.

Sobash, R. A., J. S. Kain, D. R. Bright, A. R. Dean, M. C. Coniglio, S. J. Weiss, J. J. Levit, 2009: Forecast guidance for severe thunderstorms based on identification of extreme phenomena in convection-allowing model forecasts. Preprints, 23rd Conference on Weather Analysis and Forecasting/19th Conference on Numerical Weather Prediction, Omaha, NE, USA, Amer. Meteor. Soc., CD-ROM, 4B.6.

Available online at http://ams.confex.com/ams/23WAF19NWP/techprogram/paper_154328.htm.

Stensrud, D. J., 2007: Parameterization Schemes: Keys to Understanding Numerical Weather Prediction Models. Cambridge University Press, 459 pp.

2008 Office of Oceanic and Atmospheric Research (OAR) Outstanding Scientific Paper Award - Special Recognition

Numerical weather prediction models play an increasingly important role in meteorology, both in short- and medium-range forecasting and global climate change studies. Arguably, the most important components of any numerical weather prediction model are the subgrid-scale parameterization schemes. These parameterization schemes determine the amount of energy that reaches the Earth's surface; determine the evolution of the planetary boundary layer; decide when subgrid-scale clouds and convection develop and produce rainfall; and determine the influence of subgrid-scale orography on the atmosphere. The analysis and understanding of parameterization schemes is a key aspect of numerical weather prediction.

This is the first book to provide in-depth explorations of the most commonly used types of parameterization schemes that influence short-range weather forecasts and global climate models. Each chapter covers a different type of parameterization scheme, starting with an overview explaining why each scheme is needed, and then reviewing the basic theory behind it. Several parameterizations are summarized and compared, followed by a discussion of their limitations. Review questions at the end of each chapter enable readers to monitor their understanding of the topics covered, and solutions are available at www.cambridge.org/9780521865401.

Stensrud, D. J., N. Yussouf, 2005: Bias-corrected short-range ensemble forecasts of near surface variables. Meteorological Applications, 12, 217-230.

A multimodel short-range ensemble forecasting system created as part of a National Oceanic and Atmospheric Administration program on improved high temperature forecasting during the summer of 2003 is evaluated. Results from this short-range ensemble system indicate that using the past complete 12 days of forecasts to bias correct today’s forecast yields ensemble mean forecasts of 2-m temperature, 2-m dewpoint temperature, and 10-m wind speed that are competitive with or better than those available from any of the model output statistics presently generated operationally in the United States. However, the bias-corrected ensemble system provides more than just the ensemble mean forecast. Probabilities produced by this system are skillful and reliable, and have been found to be valuable when evaluated in a cost-loss model. The ensemble appears to provide better guidance for more unlikely events, such as very warm temperatures, that likely have the greatest economic significance. Industries that are sensitive to the weather, such as power companies, transportation, and agriculture, may benefit from the probability information provided. Thus, it is possible to develop post-processing for short-range ensemble forecasting systems that is competitive with or better than traditional post-processing techniques, thereby allowing the rapid production of useful and accurate guidance forecasts of many near surface variables.

Stensrud, D. J., M. C. Coniglio, R. P. Davies-Jones, J. S. Evans, 2005: Comments on “A Theory for Strong Long-Lived Squall Lines” Revisited. Journal of the Atmospheric Sciences, 62, 2989-2996.

No abstract.

Stensrud, D. J., H. E. Brooks, 2005: The future of peer review?. Weather and Forecasting, 20, 825-826.

No abstract.

Stensrud, D. J., 2006: NEHRTP Workshop: Improving weather forecast services used by the electric utility industry. Bulletin of the American Meteorological Society, 87, 499-501.

No abstract.

Stensrud, D. J., N. Yussouf, M. E. Baldwin, J. T. McQueen, J. Du, B. Zhou, B. Ferrier, G. Manikin, F. M. Ralph, J. M. Wilczak, A. B. White, I. Djlalova, J. W. Bao, R. J. Zamora, S. G. Benjamin, P. A. Miller, T. L. Smith, T. Smirnova, M. F. Barth, 2006: The New England High-Resolution Temperature Program. Bulletin of the American Meteorological Society, 87, 491-498.

The New England High-Resolution Temperature Program seeks to improve the accuracy of summertime 2-m temperature and dewpoint temperature forecasts in the New England region through a collaborative effort between the research and operational components of the National Oceanic and Atmospheric Administration (NOAA). The four main components of this program are 1) improved surface and boundary layer observations for model initialization, 2) special observations for the assessment and improvement of model physical process parameterization schemes, 3) using model forecast ensemble data to improve upon the operational forecasts for near surface variables, and 4) transfering knowledge gained to commercial weather services and end users. Since 2002 this program has enhanced surface temperature observations by adding 70 new automated Cooperative Observer Program (COOP) sites, identified and collected data from over 1000 non-NOAA mesonet sites, and deployed boundary layer profilers and other special instrumentation throughout the New England region to better observe the surface energy budget. Comparisons of these special data sets with numerical model forecasts indicate that near surface temperature errors are strongly correlated to errors in the model predicted radiation fields. The attenuation of solar radiation by aerosols is one potential source of the model radiation bias. However, even with these model errors, results from bias-corrected ensemble forecasts are more accurate than the operational model output statistics (MOS) forecasts for 2-m temperature and dewpoint temperature, while also providing reliable forecast probabilities. Discussions with commerical weather vendors and end users have emphasized the potential economic value of these probabilistic ensemble-generated forecasts.

Stensrud, D. J., N. Yussouf, 2007: Reliable probabilistic quantitative precipitation forecasts from a short-range ensemble forecasting system. Weather and Forecasting, 22, 3-17.

A simple binning technique is developed to produce reliable 3-h probabilistic quantitative precipitation forecasts (PQPFs) from the National Centers for Environmental Prediction (NCEP) multimodel shortrange ensemble forecasting system obtained during the summer of 2004. The past 12 days’ worth of forecast 3-h accumulated precipitation amounts and observed 3-h accumulated precipitation amounts from the NCEP stage-II multisensor analyses are used to adjust today’s 3-h precipitation forecasts. These adjustments are done individually to each of ensemble members for the 95 days studied. Performance of the adjusted ensemble precipitation forecasts is compared with the raw (original) ensemble predictions. Results show that the simple binning technique provides significantly more skillful and reliable PQPFs of rainfall events than the raw forecast probabilities. This is true for the base 3-h accumulation period as well as for accumulation periods up to 48 h. Brier skill scores and the area under the relative operating characteristics curve also indicate that this technique yields skillful probabilistic forecasts. The performance of the adjusted forecasts also progressively improves with the increased accumulation period. In addition, the adjusted ensemble mean QPFs are very similar to the raw ensemble mean QPFs, suggesting that the method does not significantly alter the ensemble mean forecast. Therefore, this simple postprocessing scheme is very promising as a method to provide reliable PQPFs for rainfall events without degrading the ensemble mean forecast.

Stensrud, D. J., N. Yussouf, D. C. Dowell, M. C. Coniglio, 2009: Assimilating surface data into a mesoscale model ensemble: Cold pool analyses from spring 2007. Atmos. Res., 93, 207-220.

Hourly mesoscale analyses are created through an ensemble Kalman filter assimilation of 2-m potential temperature, 2-m dewpoint temperature, and 10-m wind observations into the Weather Research and Forecast (WRF-ARW) model using the Data Assimilation Research Testbed (DART) framework. Hourly analyses are created from 1300 UTC to 0600 UTC each day from 15 March through 30 June 2007. Two cases in which a distinct isolated mesoscale convective system is seen in observations are selected for further examination. Results indicate that the ensemble mean surface analyses reproduce the surface mesoscale features associated with cold pools underneath these precipitating systems in agreement with available observations. However, the ensemble Kalman filter also is able to produce vertical motion fields and vertical structures within and above the boundary layer that are consistent with these observed surface features. In particular, a rear inflow jet is produced at roughly 1 km above ground level behind the main convective line along with an “onion” sounding along the back edge of the trailing stratiform precipitation region near a surface mesolow. Both of these structures are known to be associated with MCSs and the ability of the ensemble Kalman filter assimilation to produce these important mesoscale features is encouraging.

Stensrud, D. J., M. Xue, L. J. Wicker, K. E. Kelleher, M. P. Foster, J. T. Schaefer, R. S. Schneider, S. G. Benjamin, S. S. Weygandt, J. T. Ferree, J. P. Tuell, 2009: Convective-scale warn on forecast: A vision for 2020. Bulletin of the American Meteorological Society, 90, 1487-1499.

The National Oceanic and Atmospheric Administration’s (NOAA’s) National Weather Service (NWS) issues warnings for severe thunderstorms, tornadoes, and flash floods since these phenomena are a threat to life and property. These warnings are presently based upon either visual confirmation of the phenomena or the observational detection of proxy signatures that are largely based upon radar observations. Convective-scale weather warnings are unique in the NWS by having little reliance on direct numerical forecast guidance. Since increasing severe thunderstorm, tornado, and flash flood warning lead times is a key NOAA strategic mission goal designed to reduce the loss of life, injury, and economic costs of these high impact weather phenomena, a new warning paradigm is needed in which numerical model forecasts play a larger role in convective-scale warnings. This new paradigm shifts the warning process from warn-on-detection to warn-on-forecast and has the potential to dramatically increase warning lead times.

A warn-on-forecast system is envisioned as a probabilistic convective-scale ensemble analysis and forecast system that assimilates in-storm observations into a high-resolution convection-resolving model ensemble. The building blocks needed for such a system are presently available and initial research results clearly illustrate the value of radar observations to the production of accurate analyses of convective weather systems and improved forecasts. While a number of scientific and cultural challenges still need to be overcome, the potential benefits are significant. A probabilistic convective-scale warn-on-forecast system is a vision worth pursuing.

Stensrud, D. J., J. Gao, 2010: Importance of Horizontally Inhomogeneous Environmental Initial Conditions to Ensemble Storm-Scale Radar Data Assimilation and Very Short-Range Forecasts. Monthly Weather Review, 138, 1250-1272.

The assimilation of operational Doppler radar observations into convection-resolving numerical weather prediction models for very short-range forecasting represents a significant scientific and technological challenge. Numerical experiments over the past few years indicate that convective-scale forecasts are sensitive to the details of the data assimilation methodology, the quality of the radar data, the parameterized microphysics, and the storm environment. In this study, the importance of horizontal environmental variability to very short-range (0–1 h) convective-scale ensemble forecasts initialized using Doppler radar observations is investigated for the 4–5 May 2007 Greensburg, Kansas, tornadic thunderstorm event. Radar observations of reflectivity and radial velocity from the operational Doppler radar network at 0230 UTC 5 May 2007, during the time of the first large tornado, are assimilated into each ensemble member using a three-dimensional variational data assimilation system (3DVAR) developed at the Center for Analysis and Prediction of Storms (CAPS). Very short-range forecasts are made using the nonhydrostatic Advanced Regional Prediction System (ARPS) model from each ensemble member and the results are compared with the observations. Explicit three-dimensional environmental variability information is provided to the convective-scale ensemble using analyses from a 30-km mesoscale ensemble data assimilation system. Comparisons between convective-scale ensembles with initial conditions produced by 3DVAR using 1) background fields that are horizontally homogeneous but vertically inhomogeneous (i.e., have different vertical environmental profiles) and 2) background fields that are horizontally and vertically inhomogeneous are undertaken. Results show that the ensemble with horizontally and vertically inhomogeneous background fields provides improved predictions of thunderstorm structure, mesocyclone track, and low-level circulation track than the ensemble with horizontally homogeneous background fields. This suggests that knowledge of horizontal environmental variability is important to successful convective-scale ensemble predictions and needs to be included in real-data experiments.

Stensrud, D. J., J. Gao, T. M. Smith, K. L. Manross, J. Brogden, V. Lakshmanan, 2010: A realtime weather-adaptive 3DVAR analysis system with automatic storm positioning and on-demand capability. Preprints, 25th Conference on Severe Local Storms, Denver, CO, USA, AMS, CD-ROM, 8B.1.

Radar is a fundamental tool for severe storm monitoring and nowcasting activities. Forecasters examine real-time WSR-88D observations from multiple radars, other remote sensing tools, severe weather detection algorithms, and use their considerable experience and situational awareness to issue severe storm warnings that help protect the public from hazardous weather events. Escalating data flow rates from new sensors and applications, however, will make it challenging for forecasters to make the best use of all the available data in warning operations. In this study, we investigate the possibility of identifying supercells with a real-time, dynamically-adaptive three-dimensional variational data assimilation (3DVAR) system that incorporates all available radar observations. A storm positioning program is implemented in the 3DVAR system based on the National Severe Storm Laboratory (NSSL) WDSS-II two-dimensional composite reflectivity product. The system has the ability to automatically detect and analyze severe local hazardous weather by identifying mesocyclones at high spatial resolution (1km horizontal resolution) and high time frequency (every 5 minutes) using data primarily from the national WSR-88D radar network and NCEP's North American Mesoscale (NAM) model product. The analysis can also be performed with on-demand capability in which end-users (or forecasters) set up the location of the analysis domain in real time based on the current weather situation. Although still in the early development stage, this system performed very well during the spring of 2010. Many severe weather events, such as the Mississippi tornadoes on April 24th, Arkansas tornadoes on April 26th, and Oklahoma/Kansas tornadoes and hailstorms on May 10th, May 16th, May 19th, May 25th were all successfully detected and analyzed.

The objectivity of the procedure ensures that (i) all available information, including all nearby WSR-88Ds and NAM high resolution analysis and forecast products, are used, (ii) physically-consistent gridded data are provided to forecasters to help make their warning decisions in a timely manner, and (iii) the problem of subjectivity, inherent to some arbitrary criteria in some severe weather detection algorithms, is avoided. Furthermore, the analysis system can be also run offline, and this enables, for example, the study of a specific area in greater detail or the investigation of the evolution and lifetime of certain kinds of severe weather. The performance of the system will be accessed and discussed in the conference.

Stolzenburg, M., T. C. Marshall, W. D. Rust, E. Bruning, D. R. MacGorman, T. Hamlin, 2007: Electric field values observed near lightning flash initiations. Geophysical Research Letters, 34, L04804-L04804.

From a dataset of about 250 soundings of electric field (E), nine were adversely affected by lightning. These soundings are interpreted as ending near lightning initiation locations. Scaled to standard pressure, the largest observed E was 626 kV m−1 and the largest estimated E was 929 kV m−1. E exceeded runaway breakdown threshold, RBth, by factors of 1.1–3.3 before each flash, and overvoltages were 1.4–4.3. Seven cases had rapid E increases (rates of 11–100 kV m−1 s−1) in the few seconds before the flash, and in three the maximum E occurred 3 s or more before the flash. A tenth sounding with E > RBth for 38 s had subsequent lightning initiate 2 km from the balloon; one channel came within 400 m, but the flash and large E did not adversely affect the instruments. The findings suggest that E > RBth is a necessary condition for lightning initiation, but it is not sufficient.

Available online at http://www.agu.org/pubs/crossref/2007/2006GL028777.shtml.

Straka, J., E. Mansell, D. MacGorman, E. Bruning, C. L. Ziegler, 2007: Comparison of modeled and observed electrical charging and lightning in a low-precipitation supercell storm during TELEX. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, International Commission on Atmospheric Electricity, 272-275.

Stuart, N. A., P. S. Market, B. Telfeyan, G. M. Lackmann, K. Carey, H. E. Brooks, B. C. Motta, K. Reeves, 2006: The future of humans in an increasingly automated forecast process. Bulletin of the American Meteorological Society, 87, 1-6.

The meteorological community is considering new roles for forecasters as increased accuracy in computer-generated weather forecasts continues to reduce the need for human intervention.

Available online at http://www.nssl.noaa.gov/users/brooks/public_html/papers/stuart.pdf.

Suarez, A., H. D. Reeves, D. Wheatley, M. Coniglio, 2012: Comparison of Ensemble Kalman Filter–Based Forecasts to Traditional Ensemble and Deterministic Forecasts for a Case Study of Banded Snow. Weather and Forecasting, 27, 85-105.

The ensemble Kalman filter (EnKF) technique is compared to other modeling approaches for a case study of banded snow. The forecasts include a 12- and 3-km grid-spaced deterministic forecast (D12 and D3), a 12-km 30-member ensemble (E12), and a 12-km 30-member ensemble with EnKF-based four- dimensional data assimilation (EKF12). In D12 and D3, flow patterns are not ideal for banded snow, but they have similar precipitation accumulations in the correct location. The increased resolution did not improve the quantitative precipitation forecast. The E12 ensemble mean has a flow pattern favorable for banding and precipitation in the approximate correct location, although the magnitudes and probabilities of relevant features are quite low. Six members produced good forecasts of the flow patterns and the precipitation structure. The EKF12 ensemble mean has an ideal flow pattern for banded snow and the mean produces banded precipitation, but relevant features are about 100 km too far north. The EKF12 has a much lower spread than does E12, a consequence of their different initial conditions. Comparison of the initial ensemble means shows that EKF12 has a closed surface low and a region of high low- to midlevel humidity that are not present in E12. These features act in concert to produce a stronger ensemble-mean cyclonic system with heavier precipitation at the time of banding.

Available online at http://dx.doi.org/10.1175/WAF-D-11-00030.1.

Taylor, A. A., L. M. Leslie, D. J. Stensrud, 2005: Forecasts of near-surface variables using a coupled atmosphere-land surface model. 19th Conference on Hydrology, San Diego, CA, USA, American Meteorological Society, 1.6.

Thompson, W., S. Burk, J. Lewis, 2005: Fog and low clouds in a coastally trapped disturbance. J. Geophysical Research, 110, .

Thompson, W., S. Burk, J. Lewis, 2005: Fog and low clouds in a coastally trapped disturbance. Journal of Geophysical Research - D: Atmospheres, 110, .

Trapp, R. J., S. A. Tessendorf, E. S. Godfrey, H. E. Brooks, 2005: Tornadoes from Squall Lines and Bow Echoes. Part I: Climatological Distribution. Weather and Forecasting, 20, 23-34.

The primary objective of this study was to estimate the percentage of U.S. tornadoes that are spawned annually by squall lines and bow echoes, or quasi-linear convective systems (QLCSs). This was achieved by examining radar reflectivity images for every tornado event recorded during 1998-2000 in the contiguous United States. Based on these images, the type of storm associated with each tornado was classified as cell, QLCS, or other. Of the 3828 tornadoes in the database, 79% were produced by cells, 18% were produced by QLCSs, and the remaining 3% were produced by other storm types, primarily rainbands of landfallen tropical cyclones. Geographically, these percentages as well as those based on tornado days exhibited wide variations. For example, 50% of the tornado days in Indiana were associated with QLCSs. In an examination of other tornado attributes, statistically more weak (F1) and fewer strong (F2-F3) tornadoes were associated with QLCSs than with cells. QLCS tornadoes were more probable during the winter months than were cells. And finally, QLCS tornadoes displayed a comparatively higher and statistically significant tendency to occur during the late night/early morning hours. Further analysis revealed a disproportional decrease in F0-F1 events during this time of day, which led the authors to propose that many (perhaps as many as 12% of the total) weak QLCSs tornadoes were not reported.

Trapp, R. J., N. S. Diffenbaugh, H. E. Brooks, M. E. Baldwin, E. D. Robinson, J. S. Pal, 2007: Changes in severe thunderstorm environment frequency during the 21st century caused by anthropogenically enhanced global radiative forcing. Proceedings of the National Academy of Sciences of the United States of America, 104, 19723.

Severe thunderstorms comprise an extreme class of deep convective clouds and produce high-impact weather such as destructive surface winds, hail, and tornadoes. This study addresses the question of how severe thunderstorm frequency in the United States might change because of enhanced global radiative forcing associated with elevated greenhouse gas concentrations. We use global climate models and a high-resolution regional climate model to examine the larger-scale (or "environmental") meteorological conditions that foster severe thunderstorm formation. Across this model suite, we find a net increase during the late 21st century in the number of days in which these severe thunderstorm environmental conditions (NDSEV) occur. Attributed primarily to increases in atmospheric water vapor within the planetary boundary layer, the largest increases in NDSEV are shown during the summer season, in proximity to the Gulf of Mexico and Atlantic coastal regions. For example, this analysis suggests a future increase in NDSEV of 100% or more in locations such as Atlanta, GA, and New York, NY. Any direct application of these results to the frequency of actual storms also must consider the storm initiation.

Van Cooten, S., K. E. Kelleher, K. W. Howard, J. Zhang, J. J. Gourley, J. S. Kain, K. Nemunaitis-Monroe, A. Arthur, C. Langston, Z. Flamig, H. Moser, . et al., 2011: The CI-FLOW Project: A System for Total Water Level Prediction from the Summit to the Sea. Bulletin of the American Meteorological Society, 92, 1427-1442.

The objective of the Coastal and Inland Flooding Observation and Warning (CI-FLOW) project is to prototype new hydrometeorologic techniques to address a critical NOAA service gap: routine total water level predictions for tidally influenced watersheds. Since February 2000, the project has focused on developing a coupled modeling system to accurately account for water at all locations in a coastal watershed by exchanging data between atmospheric, hydrologic, and hydrodynamic models. These simulations account for the quantity of water associated with waves, tides, storm surge, rivers, and rainfall, including interactions at the tidal/surge interface.

Within this project, CI-FLOW addresses the following goals: i) apply advanced weather and oceanographic monitoring and prediction techniques to the coastal environment; ii) prototype an automated hydrometeorologic data collection and prediction system; iii) facilitate interdisciplinary and multiorganizational collaborations; and iv) enhance techniques and technologies that improve actionable hydrologic/hydrodynamic information to reduce the impacts of coastal flooding. Results are presented for Hurricane Isabel (2003), Hurricane Earl (2010), and Tropical Storm Nicole (2010) for the Tar–Pamlico and Neuse River basins of North Carolina. This area was chosen, in part, because of the tremendous damage inflicted by Hurricanes Dennis and Floyd (1999). The vision is to transition CI-FLOW research findings and technologies to other U.S. coastal watersheds.

Available online at http://journals.ametsoc.org/doi/pdf/10.1175/2011BAMS3150.1.

Van Cooten, S., K. Kelleher, K. Howard, J. Zhang, J. J. Gourley, C. Langston, V. Farmer, K. Monroe, Z. L. Flamig, H. Moser, R. Kolar, Y. Hong, K. Dresback, E. Tromble, H. Vergara, R. Luettich, B. Blanton, K. Galuppi, C. A. Blain, J. F. Thigpen, K. Mosher, D. Figursky, M. Moneypenny, J. Orrock, R. Bandy, C. Goodall, J. Kelley, J. Greenlaw, M. Wengren, D. Eslinger, J. Payne, J. Feldt, J. Schmidt, T. Hamill, R. H. Bacon, R. Stickney, L. Spence, 2011: Coastal and Inland FLooding Observation and Warning (CI-FLOW) Project-An Assesment of Research Outcomes From An Integrated Hydrologic Prediction System for Coastal Watersheds. Preprints, 25th Conference on Hydrology, Seattle, WA, USA, American Meteorological Society, 7.4.

The objective of the Coastal and Inland FLooding Observation and Warning (CI-FLOW) project is to develop and prototype new hydrometeorological techniques to address a critical NOAA service gap: routine total water level predictions for tidally-influenced watersheds. Since February 2000, the project has focused on developing a system to accurately account for water at all locations in a coastal watershed. The CI-FLOW computing framework interactively exchanges data between atmospheric, river, and ocean models to produce water quantity simulations upstream and downstream of the tidal plain, including shorelines. These simulations account for the quantity of water associated with waves, tides, storm surge, rivers, and rainfall, inclusive of interactions at the tidal/surge interface.

Within this framework, CI-FLOW accomplishes the following goals: 1) apply advanced weather monitoring and prediction techniques to the coastal environment; 2) prototype an automated hydrometeorological data collection and prediction system; 3) facilitate interdisciplinary and multi-organizational collaborations; and 4) enhance techniques and technologies that improve actionable hydrologic information to reduce the impacts of coastal floods/flash floods. Results are presented for Hurricane Isabel, the first test of the integrated framework, for the Tar-Pamlico and Neuse river basins of North Carolina. This area was chosen, in part, because of the tremendous damage inflicted by Hurricanes Dennis and Floyd in September 1999. However, the vision is to transition CI-FLOW research findings and technologies to other U.S. coastal watersheds

Available online at http://ams.confex.com/ams/91Annual/flvgateway.cgi/id/17363?recordingid=17363.

Vasiloff, S. V., D. J. Seo, K. W. Howard, J. Zhang, D. H. Kitzmiller, M. G. Mullusky, W. F. Krajewski, E. A. Brandes, R. M. Rabin, D. S. Berkowitz, H. E. Brooks, J. A. McGinley, R. J. Kuligowski, B. G. Brown, 2007: Improving QPE and Very Short Term QPF: An Initiative for a Community-Wide Integrated Approach. Bulletin of the American Meteorological Society, 88, 1899-1911.

Accurate quantitative precipitation estimates (QPE) and very short term quantitative precipitation forecasts (VSTQPF) are critical to accurate monitoring and prediction of water-related hazards and water resources. While tremendous progress has been made in the last quarter-century in many areas of QPE and VSTQPF, significant gaps continue to exist in both knowledge and capabilities that are necessary to produce accurate high-resolution precipitation estimates at the national scale for a wide spectrum of users. Toward this goal, a national next-generation QPE and VSTQPF (Q2) workshop was held in Norman, Oklahoma, on 28–30 June 2005. Scientists, operational forecasters, water managers, and stakeholders from public and private sectors, including academia, presented and discussed a broad range of precipitation and forecasting topics and issues, and developed a list of science focus areas. To meet the nation's needs for the precipitation information effectively, the authors herein propose a community-wide integrated approach for precipitation information that fully capitalizes on recent advances in science and technology, and leverages the wide range of expertise and experience that exists in the research and operational communities. The concepts and recommendations from the workshop form the Q2 science plan and a suggested path to operations. Implementation of these concepts is expected to improve river forecasts and flood and flash flood watches and warnings, and to enhance various hydrologic and hydrometeorological services for a wide range of users and customers. In support of this initiative, the National Mosaic and Q2 (NMQ) system is being developed at the National Severe Storms Laboratory to serve as a community test bed for QPE and VSTQPF research and to facilitate the transition to operations of research applications. The NMQ system provides a real-time, around-the-clock data infusion and applications development and evaluation environment, and thus offers a community-wide platform for development and testing of advances in the focus areas.

Vera, C., J. Beaz, M. Douglas, C. Emmanuel, J. Marengo, J. Meitin, M. Nicolini, J. Nouges-Paegle, J. Paegle, O. Penalba, P. Salio, C. Saulo, M. A. Silva-Dias, P. Silva-Dias, E. Zipser, 2006: The South American Low-Level Jet Experiment. Bulletin of the American Meteorological Society, 87, 63-77.

Verbout, S. M., L. M. Leslie, H. E. Brooks, D. Schultz, D. Karoly, 2005: Tornado outbreaks associated with land-falling tropical cyclones in the Atlantic Basin. Preprints, 6th Conference on Coastal Atmospheric and Oceanic Prediction and Processes, San Diego, CA, USA, American Meteorological Society, CD-ROM, 7.1.

Available online at http://ams.confex.com/ams/Annual2005/techprogram/paper_84926.htm.

Verbout, S. M., H. E. Brooks, L. M. Leslie, D. M. Schultz, 2006: Evolution of the U.S. tornado database: 1954-2004. Weather and Forecasting, 21, 86-93.

Over the last 50 yr, the number of tornadoes reported in the United States has doubled from about 600 per year in the 1950s to around 1200 in the 2000s. This doubling is likely not related to meteorological causes alone. To account for this increase a simple least squares linear regression was fitted to the annual number of tornado reports. A "big tornado day" is a single day when numerous tornadoes and/or many tornadoes exceeding a specified intensity threshold were reported anywhere in the country. By defining a big tornado day without considering the spatial distribution of the tornadoes, a big tornado day differs from previous definitions of outbreaks. To address the increase in the number of reports, the number of reports is compared to the expected number of reports in a year based on linear regression. In addition, the F1 and greater Fujita-scale record was used in determining a big tornado day because the F1 and greater series was more stationary over time as opposed to the F2 and greater series. Thresholds were applied to the data to determine the number and intensities of the tornadoes needed to be considered a big tornado day. Possible threshold values included fractions of the annual expected value associated with the linear regression and fixed numbers for the intensity criterion. Threshold values of 1.5% of the expected annual total number of tornadoes and/or at least 8 F1 and greater tornadoes identified about 18.1 big tornado days per year. Higher thresholds such as 2.5% and/or at least 15 F1 and greater tornadoes showed similar characteristics, yet identified approximately 6.2 big tornado days per year. Finally, probability distribution curves generated using kernel density estimation revealed that big tornado days were more likely to occur slightly earlier in the year and have a narrower distribution than any given tornado day.

Available online at http://www.cimms.ou.edu/~schultz/pubs/verboutetal06.pdf.

Verbout, S. M., D. M. Schultz, L. M. Leslie, H. E. Brooks, D. J. Karoly, K. L. Elmore, 2007: Tornado outbreaks associated with landfalling hurricanes in the north Atlantic Basin: 1954–2004. Meteorology and Atmospheric Physics, 97, 255-271.

Tornadoes are a notable potential hazard associated with landfalling hurricanes. The purpose of this paper is to discriminate hurricanes that produce numerous tornadoes (tornado outbreaks) from those that do not (nonoutbreaks). The data consists of all hurricane landfalls that affected the United States from the North Atlantic basin from 1954 to 2004 and the United States tornado record over the same period. Because of the more than twofold increase in the number of reported tornadoes over these 51 years, a simple least-squares linear regression ("the expected number of tornadoes") was fit to the annual number of tornado reports to represent a baseline for comparison.

The hurricanes were sorted into three categories. The first category, outbreak hurricanes, was determined by hurricanes associated with the number of tornado reports exceeding a threshold of 1.5% of the annual expected number of tornadoes and at least 8 F1 and greater tornadoes during the time of landfall (from outer rainbands reaching shore to dissipation of the system). Eighteen hurricane landfalls were classified as outbreak hurricanes. Second, 37 hurricanes having less han 0.5% of the annual expected number of tornadoes were classified as nonoutbreak landfalls. Finally, 28 hurricanes that were neither outbreak nor nonoutbreak hurricanes were classified as midclass hurricane landfalls.

Stronger hurricanes are more likely to produce tornado outbreaks than weaker hurricanes. While 78% of outbreak hurricanes were category 2 or greater at landfall, only 32% of nonoutbreak hurricanes were category 2 or greater at landfall. Hurricanes that made landfall along the southern coast of the United States and recurved northeastward were more likely to produce tornadoes than those that made landfall along the east coast or those that made landfall along the southern coast but did not recurve. Recurvature was associated with a 500-hPa trough in the jet stream, which also contributed to increased deep-layer shear through the hurricane, favoring mesocyclogenesis, and increased the low-level shear, favoring tornadogenesis. The origin of the hurricane, date of landfall, and El Niño-Southern Oscillation phase do not appear to be factors in outbreak hurricane creation. The results of this study help clarify inconsistencies in the previous literature regarding tornado occurrences in landfalling hurricanes.

Available online at http://www.springerlink.com/content/8132257282886516/fulltext.pdf.

Vich, M., R. Romero, H. E. Brooks, 2011: Ensemble prediction of Mediterranean high-impact events using potential vorticity perturbations. Part I: Comparison against the multiphysics approach. Atmospheric Research, 102, 227-241.

The western Mediterranean is a very cyclogenetic area and many of the cyclones developed over this region are associated with high-impact weather phenomena that affect the society of the coastal countries. Two ensemble prediction systems (EPSs) based on multiphysics and perturbed initial and boundary conditions (IBC) are designed in order to improve the forecast of these heavy rain episodes. The MM5 mesoscale model nested in the ECMWF forecast fields provides the simulations, run at 22.5 km resolution for a two-day period.

The multiphysics ensemble combines different model physical parameterization schemes while the other ensemble perturbs the initial state and boundary forcing of the model with the
aid of a PV inversion scheme. A PV error climatology derived from the large-scale fields allows to perturb the ECMWF PV fields using the appropriate error range.

The verification procedure indicates that even though both EPSs are skillful, the perturbed IBC ensemble is more proficient than the multiphysics EPS for the 19 Mediterranean cyclonic events with heavy rain considered in the study. Therefore the results show a more dominant role of the uncertainties in the initial and boundary conditions than the model error, although both of them contribute significantly to improve the predictability of Western Mediterranean high impact weather situations.

Wandishin, M. S., D. J. Stensrud, S. L. Mullen, L. J. Wicker, 2008: On the Predictability of Mesoscale Convective Systems: Two-Dimensional Simulations. Weather and Forecasting, 23, 773-785.

Mesoscale convective systems (MCSs) are a dominant climatological feature of the central United States and are responsible for a substantial fraction of warm season rainfall. Yet very little is known about the predictability of MCSs. To help alleviate this situation, a series of ensemble simulations of an MCS are performed on a two-dimensional, storm-scale (dx ~ 1 km) model. Ensemble member perturbations in wind speed, relative humidity, and instability are based on current 24-h forecast errors from the North American
Model (NAM). The ensemble results thus provide an upper bound on the predictability of mesoscale convective systems within realistic estimates of environmental uncertainty, assuming successful convective initiation.

The simulations are assessed by considering an ensemble member a success when it reproduces a convective system of at least 20 km in length (roughly the size of two convective cells) within 100 km on either side of the location of the MCS in the control run. By that standard, MCSs occur roughly 70% of the time for perturbation magnitudes consistent with 24-h forecast errors. Reducing the perturbations for all fields to one-half the 24-h error values increases the MCS success rate to over 90%. The same improvement in
forecast accuracy would lead to a 30%–40% reduction in maximum surface wind speed uncertainty and a roughly 20% reduction in the uncertainty in maximum updraft strength, and initially slower growth in the
uncertainty in the size of the MCS. However, the occurrence of MCSs drops below 50% as the midlayer mean relative humidity falls below 65%. The response of the model to reductions in forecast errors for instability, moisture, and wind speed is not consistent and cannot be easily generalized, but each can have a substantial impact on forecast uncertainty.

Wandishin, M. S., D. J. Stensrud, S. L. Mullen, L. J. Wicker, 2010: On the predictability of mesoscale convective systems: Three-dimensional simulations. Monthly Weather Review, 138, 863-885.

Mesoscale convective systems (MCSs) are a dominant climatological feature of the central United States and are responsible for a substantial fraction of warm-season rainfall. Yet very little is known about the predictability of MCSs. To help address this situation, a previous paper by the authors examined a series of ensemble MCS simulations using a two-dimensional version of a storm-scale (dx = 1 km) model. Ensemble member perturbations in the preconvective environment, namely, wind speed, relative humidity, and convective instability, are based on current 24-h forecast errors from the North American Model (NAM). That work is now extended using a full three-dimensional model.

Results from the three-dimensional simulations of the present study resemble those found in two dimensions. The model successfully produces an MCS within 100 km of the location of the control run in around 70% of the ensemble runs using perturbations to the preconvective environment consistent with 24-h forecast errors, while reducing the preconvective environment uncertainty to the level of current analysis errors improves the success rate to nearly 85%. This magnitude of improvement in forecasts of environmental conditions would represent a radical advance in numerical weather prediction. The maximum updraft and surface wind forecast uncertainties are of similar magnitude to their two-dimensional counterparts. However, unlike the two-dimensional simulations, in three dimensions, the improvement in the forecast uncertainty of storm features requires the reduction of preconvective environmental uncertainty for all perturbed variables. The MCSs in many of the runs resemble bow echoes, but surface winds associated with these solutions, and the perturbation profiles that produce them, are nearly indistinguishable from the nonbowing solutions, making any conclusions about the bowlike systems difficult.

Wang, B., J. Zhang, W. Xia, K. Howard, X. Xu, 2008: Analysis of radar and gauge rainfall during the warm season in Oklahoma. Preprints, The 22nd Conf. on Hydrology, New Orleans, LA, USA, Amer. Meteor. Soc., CD-ROM, P2.1.

Wang, S. Y., A. J. Clark, 2010: NAM Model forecasts of warm-season quasi-stationary frontal environments in the central United States. Weather and Forecasting, 25, 1281-1292.

Wang, S. Y., A. J. Clark, 2010: Quasi-decadal spectral peaks of tropical western Pacific SSTs as a percursor for tropical cyclone threat.. Geophysical Research Letters, 37, .

Ware, E. C., D. M. Schultz, H. E. Brooks, P. J. Roebber, S. L. Bruening, 2006: Improving snowfall forecasting by accounting for the climatological variability of snow density. Weather and Forecasting, 21, 94-103.

Accurately forecasting snowfall is a challenge. In particular, one poorly understood component of snowfall forecasting is determining the snow ratio. The snow ratio is the ratio of snowfall to liquid equivalent and is inversely proportional to the snow density. In a previous paper, an artificial neural network was developed to predict snow ratios probabilistically in three classes: heavy (1:1 < ratio < 9:1), average (9:1 <= ratio <= 15:1), and light (ratio > 15:1). A Web-based application for the probabilistic prediction of snow ratio in these three classes based on operational forecast model soundings and the neural network is now available. The goal of this paper is to explore the statistical characteristics of the snow ratio to determine how temperature, liquid equivalent, and wind speed can be used to provide additional guidance (quantitative, wherever possible) for forecasting snowfall, especially for extreme values of snow ratio. Snow ratio tends to increase as the low-level (surface to roughly 850 mb) temperature decreases. For example, mean low-level temperatures greater than −2.7°C rarely (less than 5% of the time) produce snow ratios greater than 25:1, whereas mean low-level temperatures less than −10.1°C rarely produce snow ratios less than 10:1. Snow ratio tends to increase strongly as the liquid equivalent decreases, leading to a nomogram for probabilistic forecasting snowfall, given a forecasted value of liquid equivalent. For example, liquid equivalent amounts 2.8–4.1 mm (0.11–0.16 in.) rarely produce snow ratios less than 14:1, and liquid equivalent amounts greater than 11.2 mm (0.44 in.) rarely produce snow ratios greater than 26:1. The surface wind speed plays a minor role by decreasing snow ratio with increasing wind speed. Although previous research has shown simple relationships to determine the snow ratio are difficult to obtain, this note helps to clarify some situations where such relationships are possible.

Available online at http://www.cimms.ou.edu/~schultz/pubs/wareetal06.pdf.

Watts, C. J., R. L. Scott, J. Garatuza-Payan, J. C. Rodriguez, J. H. Prueger, W. P. Kustas, M. Douglas, 2007: Changes in Vegetation Condition and Surface Fluxes during NAME 2004. Journal of Climate, 20, .

Weiss, S., J. Kain, L. Wicker, R. Davies-Jones, D. Bright, J. Levit, G. Carbin, M. Baldwin, 2005: Evaluating the skill of daily explicit predictions of mesocyclones in multiple high-resolution WRF model forecasts during the 2005 SPC/NSSL Spring Program. Preprints, 12th Conf. On Mesoscale Processes,, Albuquerque, NM, USA, Amer. Meteor. Soc., no preprint.

Weiss, S. J., J. S. Kain, D. R. Bright, J. J. Levit, M. Pyle, Z. I. Janjic, B. Ferrier, J. Du, M. L. Weisman, M. Xue, 2007: The NOAA Hazardous Weather Testbed: Collaborative testing of ensemble and convection-allowing WRF models and subsequent transfer to operations at the Storm Prediction Center.. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 6B.4.

Weiss, S. J., J. S. Kain, D. R. Bright, J. J. Levit, M. Pyle, Z. I. Janjic, B. S. Ferrier, J. Du, M. L. Weisman, M. Xue, 2007: The NOAA Hazardous Weather Testbed: Collaborative testing of ensemble and convection-allowing WRF models and subsequent transfer to operations at the Storm Prediction Center. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, Amer. Mete. [Available from S. J. Weiss, SPC, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Since 2003, the Storm Prediction Center (SPC) has played a leading role in testing various configurations of Short-Range Ensemble Forecast (SREF) systems and high resolution WRF models for their operational utility. These test and evaluation activities have occurred during organized collaborative activities in the NOAA Hazardous Weather Testbed (HWT) in Norman. The HWT is designed to bring research scientists, model developers, and forecasters together to work on issues of mutual interest, facilitating the rapid transfer of research to operations. This organizational framework helps researchers and model developers to better understand the operational challenges and requirements of forecasters, educates forecasters on new science and technological advances, and has accelerated the application of new modeling approaches to severe weather forecasting. This paper focuses on the use of the operational NCEP SREF and two experimental high resolution convection-allowing WRF models as complementary sources of information for SPC forecasters.

NCEP is running a 21 member multi-model, multi-analysis SREF system with enhanced physics diversity four times daily with output through 87 hours. SPC processes the grids from all SREF members and produces a large variety of products for severe weather forecasting, including standard spaghetti, mean and spread, probability, and max/min charts, as well as specialized multi-parameter convective fields and post-processed calibrated probabilities for the occurrence of thunderstorms, dry thunderstorms, and severe thunderstorms.

NCEP has also been running an experimental high resolution WRF-Non-hydrostatic Mesoscale Model (WRF-NMM4) for the SPC since April 2004; this model was recently upgraded to a 4 km grid length. And starting in November 2006, SPC forecasters have had access to output from a 4 km Advanced Research WRF (WRF-ARW4) developed by NCAR and run at the National Severe Storms Laboratory. Both WRF models are initialized from a cold start once daily at 0000 UTC using initial and lateral boundary conditions from the operational North American Mesoscale model, and provide forecasts through a 36 hour period over a domain covering approximately three-fourths of the U.S. Several unique WRF products have been developed for use by severe weather forecasters, including simulated reflectivity and measures of updraft rotation in model-generated storms.

The incorporation of SREF and high resolution WRF guidance into an operational severe weather forecasting environment already dealing with high volumes of observational and model data requires careful assessment of the unique strengths of each modeling system, and knowledge of the specific needs of SPC forecasters. Since the SPC severe weather forecast mission focuses on phenomena smaller than that predicted by mesoscale models, such as tornadoes and severe thunderstorms, the traditional forecast methodology has focused on first predicting the evolution of the mesoscale environment and then determining the spectrum of convective storms a particular environment may support. SREF output has been found to be particularly useful in quantifying the likelihood that the environment will occupy specific parts of convective parameter space, as well as the likelihood and timing for thunderstorms and severe thunderstorms to develop over Outlook-scale regions. While this can be extremely helpful to SPC forecasters, more detailed information about the intensity and mode of storms is also needed, since the type of severe weather (e.g., tornadoes, damaging wind) is often strongly related to convective mode. The value of the high resolution WRF guidance is most evident here, as it has capability to resolve near storm-scale convective characteristics, such as the development of discrete cells ahead of a line of storms, and the development of model storms with rotating updrafts.

We will examine the complementary role of SREF and high resolution WRF output during several strongly-forced and weakly-forced severe weather days during the winter and spring severe weather period and illustrate the operational application of these model datasets in the SPC decision-making process for both Convective Outlooks and Watches.

Available online at http://ams.confex.com/ams/pdfpapers/124772.pdf.

Wen, Y., Y. Hong, G. Zhang, T. J. Schuur, J. J. Gourley, Z. Flamig, K. Morris, Q. Cao, 2011: Cross validation of spaceborne radar and ground polarimetric radar aided by polarimetric echo classification of hydrometeor types. Journal of Applied Meteorology and Climatology, 50, 1389-1402.

Wheatley, D. M., D. J. Stensrud, 2010: The Impact of Assimilating Surface Pressure Observations on Severe Weather Events in a WRF Mesoscale Ensemble System. Monthly Weather Review, 138, 1673-1694.

Surface pressure observations are assimilated into a Weather Research and Forecast ensemble using an ensemble Kalman filter (EnKF) approach and the results are compared with observations for two severe weather events. Several EnKF experiments are performed to evaluate the relative impacts of two very different pressure observations: altimeter setting (a total pressure field) and 1-h surface pressure tendency. The primary objective of this study is to determine the surface pressure observation that is most successful in producing realistic mesoscale features, such as convectively driven cold pools, which often play an important role in future convective development. Results show that ensemble-mean pressure analyses produced from the assimilation of surface temperature, moisture, and winds possess significant errors in regard to mesohigh strength and location. The addition of surface pressure tendency observations within the assimilation yields limited ability to constrain such errors, while the assimilation of altimeter setting yields accurate depictions of the mesoscale pressure patterns associated with mesoscale convective systems. The mesoscale temperature patterns produced by all the ensembles are quite similar and tend to reproduce the observed features. Results suggest that even though surface pressure observations can have large cross covariances with temperature and the wind components, the resulting analyses fail to improve upon the EnKF temperature and wind analyses that exclude the surface pressure observations. Ensemble forecasts following the assimilation period show the potential to improve short-range forecasting of surface pressure.

Wheatley, D. M., D. J. Stensrud, D. C. Dowell, N. Yussouf, 2012: Application of a WRF Mesoscale Data Assimilation System to Springtime Severe Weather Events 2007-09. Monthly Weather Review, 140, 1539-1557.

An ensemble-based data assimilation system using the Weather Research and Forecasting (WRF) model has been used to initialize forecasts of prolific severe weather events from springs 2007-2009. These experiments build on previous work that has shown the ability of ensemble Kalman filter (EnKF) data assimilation to produce realistic mesoscale features, such as drylines and convectively driven cold pools, which often play an important role in future convective development. For each event in this study, severe weather parameters are calculated from an experimental ensemble forecast started from EnKF analyses, and then compared to a control ensemble forecast in which no ensemble-based data assimilation is performed. Root mean square errors for surface observations averaged across all events are generally smaller for the experimental ensemble over the 0-6 h forecast period. At model grid points nearest tornado reports, the ensemble-mean significant tornado parameter (STP) and the probability of STP > 1 are often greater in the experimental 0-6 h ensemble forecasts than in the control forecasts. Likewise, the probability of MCS Maintenance Probability (MMP) is often greater with the experimental ensemble at model grid points nearest wind reports. Severe weather forecasts can be sharpened by coupling the respective severe weather parameter with the probability of measurable rainfall at model grid points. The differences between the two ensembles are found to be significant at the 95% level, suggesting that even a short period of ensemble data assimilation can yield improved forecast guidance for severe weather events.

Wulfmeyer, V., A. Behrendt, C. Kottmeier, U. Corsmeier, C. Barthlott, G. C. Craig, M. Hagen, D. Althausen, F. Aoshima, M. Arpagaus, H. S. Bauer, L. Bennett, A. Blyth, C. Brandau, C. Champollion, S. Crewell, G. Dick, P. DiGirolamo, M. Dorninger, Y. Dufournet, R. Eigenmann, R. Engelmann, C. Flamant, T. Foken, T. Gorgas, M. Grzeschik, J. Handwerker, C. Hauck, H. Hoeller, W. Junkermann, N. Kalthoff, C. Kiemle, S. Klink, M. Koenig, L. Krauss, C. N. Long, F. Madonna, S. Mobbs, B. Neiniger, S. Pal, G. Peters, G. Pigeon, E. Richard, M. W. Rotach, H. Russchenberg, T. Schwitalla, V. Smith, R. Steinacker, J. Trentmann, D. D. Turner, J. van Baelen, S. Vogt, H. Volkert, T. Weckwerth, H. Wernli, A. Wieser, M. Wirth, 2011: The convective and orographically induced precipitation study (COPS): The scientific strategy, the field phase, and first highlights.. Quarterly Journal of the Royal Meteorological Society, 137, 3-30.

Within the framework of the international field campaign COPS (Convective and Orographically-induced Precipitation Study), a large suite of state-of-the-art meteorological instrumentation was operated, partially combined for the first time. This includes networks of in situ and remote-sensing systems such as the Global Positioning System as well as a synergy of multi-wavelength passive and active remote-sensing instruments such as advanced radar and lidar systems. The COPS field phase was performed from 01 June to 31 August 2007 in a low-mountain area in southwestern Germany/eastern France covering the Vosges mountains, the Rhine valley and the Black Forest mountains. The collected data set covers the entire evolution of convective precipitation events in complex terrain from their initiation, to their development and mature phase until their decay. Eighteen Intensive Observation Periods with 37 operation days and eight additional Special Observation Periods were performed, providing a comprehensive data set covering different forcing conditions. In this article, an overview of the COPS scientific strategy, the field phase, and its first accomplishments is given. Highlights of the campaign are illustrated with several measurement examples. It is demonstrated that COPS research provides new insight into key processes leading to convection initiation and to the modification of precipitation by orography, in the improvement of quantitative precipitation forecasting by the assimilation of new observations, and in the performance of ensembles of convection-permitting models in complex terrain.

Xu, Q., 2005: Non-modal growths of symmetric perturbations produced by paired normal modes. 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, 6M4.

Xu, Q., K. Nai, L. Wei, P. Zhang, L. Wang, H. Lu, Qingyun Zhao, 2005: Progress in doppler radar data assimilation. 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, JP1J7.

Xu, Q., W. Gu, S. Gao, 2005: Nonlinear oscillations of semigeostrophic Eady waves in the presence of diffusivity. Advances in Atmospheric Sciences, 22, 49-57.

Xu, Q., 2005: Representations of inverse covariances by differential operators. Advances in Atmospheric Sciences, 22, 181-198.

Xu, Q., L. Wei, H. Lu, K. Nai, Q. Zhao, 2006: Phased-array radar data assimilation at the National Weather Radar Testbed -- Theoretical issues and practical solutions. Preprints, Fourth European Conference on Radar Meteorology, Barcelona, Spain, ERAD multiple Sponsors. See http://www.grahi.upc.edu/ERAD2006/i, 515-518.

Available online at http://www.grahi.upc.edu/ERAD2006/index.php.

Xu, Q., S. Liu, M. Xue, 2006: Background error covariance functions for vector wind analyses using Doppler radar radial-velocity observations. Quart. J. Roy. Meteor. Soc., 132, 2887-2904.

Xu, Q., K. Nai, L. Wei, 2007: An innovation method for estimating radar radial-velocity observation error and background wind error covariances. Quart. J. Roy. Meteor. Soc., 133, 407-415.

Xu, Q., 2007: Measuring information content from observations for data assimilation: Relative entropy versus Shannon entropy difference. Tellus, 59A, 198-209.

Xu, Q., 2007: Modal and non-modal symmetric perturbations. Part 1. Modal solutions and partial orthogonality. Journal of the Atmospheric Sciences, 64, 1745-1763.

Xu, Q., T. Lei, S. Gao, 2007: Modal and non-modal symmetric perturbations. Part 2. Non-modal growths measured by total perturbation energy. Journal of the Atmospheric Sciences, 64, 1764-1781.

Xu, Q., K. Nai, L. Wei, H. Lu, P. Zhang, S. Liu, D. Parrish, 2007: Estimating radar wind observation error and NCEP WRF background wind error covariances from radar radial-velocity innovations. Extended Abstracts, 18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., 1B.3.

Available online at http://ams.confex.com/ams/pdfpapers/123419.pdf.

Xu, Q., L. Wei, H. Lu, Q. Zhao, C. Qiu, 2007: Time-expanded sampling for ensemble-based filter with covariance localization: assimilation experiments with a shallow-water equation model. Preprints, 18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., 6B.1A.

Available online at http://ams.confex.com/ams/pdfpapers/123409.pdf.

Xu, Q., H. Lu, L. Wei, Q. Zhao, 2007: Studies of phased-array scan strategies for radar data assimilation. Extended Abstracts, 33rd Conference on Radar Meteorology, Cairns, Australia, Amer. Meteor. Soc., 4A.3.

Available online at http://ams.confex.com/ams/pdfpapers/122972.pdf.

Xu, Q., L. Wei, H. Lu, C. Qiu, Q. Zhao, 2008: Time-expanded sampling for ensemble-based filters: Assimilation experiments with a shallow-water equation model. Journal of Geophysical Research - D: Atmospheres, 113, .

Xu, Q., H. Lu, L. Wei, S. Gao, M. Xue, M. Tong, 2008: Time-expanded sampling for ensemble Kalman filter: Assimilation experiments with simulated Radar observations. Monthly Weather Review, 136, 2651-2667.

Xu, X., K. Howard, J. Zhang, 2008: An Automated Radar Technique for the Identification of Tropical Precipitation. Journal of Hydrometeorology, 9, 885-902.

Xu, Q., L. Wei, S. Healy, 2009: Measuring information content from observations for data assimilations: connection between different measures and application to radar scan design. Tellus, 61A, 144-153.

The previously derived formulations for using the relative entropy and Shannon entropy difference to measure information content from observations are revisited in connection with another known information measure – degrees of freedom for signal, which is defined as the statistical average of the signal part of the relative entropy. For a linear assimilation system, the statistical average of the relative entropy reduces to the Shannon entropy difference. The formulations are extended for four-dimensional variational data assimilation (4DVar). The extended formulations reveal that the information content increases (or decreases) as the model error increase (or decrease) and/or become strongly (or weakly) correlated in 4D space. These properties are also highlighted by illustrative examples, and the extended formulations are shown to be potential useful for designing optimum phased-array radar scan configurations to maximize the extractable information contents from radar observations by a 4DVar analysis system.

Xu, Q., K. Nai, L. Wei, P. Zhang, Q. Zhao, P. Harasti, 2009: A real-time radar wind data quality control and analysis system for nowcast application. Extended Abstracts, International Symposium on Nowcasting and Very Short Range Forecasting (WSN09), Whistler, Canada, WMO, CD-ROM, 3.5.

A real-time radar wind analysis system has been developed for monitoring low-level wind conditions at high spatial and temporal resolution. By ingesting real-time wind observations from KTLX radar, Oklahoma Mesonet data and NOAA Profiler Network, this system produces and displays real-time vector wind field at each selected vertical level or on each conical surface of radar scans superimposed on radar reflectivity or radial-velocity image. The products are made available to NWS Norman Forecast Office. The early system has been evaluated and used to provide real-time winds to drive high-resolution emergency response dispersion models. The key technical elements developed in the system for the radar data quality control and wind analysis are presented with illustrative examples.

Xu, Q., K. Nai, L. Wei, Q. Zhao, 2009: An unconventional approach for assimilating aliased radar radial velocities. Tellus, 61A, 621-630.

An aliasing operator is introduced to mimic the effect of aliasing that causes discontinuities in radial-velocity observations, and to modify the observation term in the costfunction for direct assimilations of aliased radar radial-velocity observations into numerical models. It is found that if the aliasing operator is treated as a part of the observation operator and applied to the analysed radial velocity in a conventional way, then the analysis is not ensured to be aliased (or not aliased) in consistency with the aliased (or not aliased) observation at every observation point. Thus, the analysis-minus-observation term contains a large alias error whenever an inconsistency occurs at an observation point. This causes fine-structure discontinuities in the costfunction. An unconventional approach is thus introduced to apply the aliasing operator to the entire analysis-minus-observation term at each observation point in the observation term of the costfunction. With this approach, the costfunction becomes smooth and concave upwards in the vicinity of the global minimum. The usefulness of this approach for directly assimilating aliased radar radial-velocity observations under certain conditions is demonstrated by illustrative examples.

Available online at http://ejournals.ebsco.com/direct.asp?ArticleID=448381488B6BEA676451.

Xu, Q., 2009: Bayesian perspective of the unconventional approach for assimilating aliased radar radial velocities. Tellus, 61A, 631-634.

The global minimization problem for directly assimilating aliased radial velocities is derived in terms of Bayesian estimation by folding the domain of the original Gaussian non-aliased observation probability density function (pdf) into the Nyquist interval. By truncating the folded tails of the observation pdf, the observation term in the costfunction recovers the aliased observation term formulated previously by an unconventional approach. This establishes the theoretical basis for the unconventional approach and quantifies the involved approximation. The alias-robust radar wind analysis developed based on the unconventional approach is also revisited from the Bayesian perspective.

Available online at http://ejournals.ebsco.com/direct.asp?ArticleID=44A7933F6CED60B8DF35.

Xu, Q., K. Nai, L. Wei, 2010: Fitting VAD wind to aliased Doppler radial-velocity observations – A minimization problem with multiple minima. Quart. J. Roy. Meteor. Soc., 136, 451-461.

When the horizontal vector wind is estimated by the traditional velocity azimuth display (VAD) analysis from radar radial-velocity observations on a selected range circle, the observations should be thoroughly de-aliased first. When the effect of aliasing is formulated into the cost function, the VAD analysis can be applied to raw aliased radial-velocity observations, but the minimization problem for the VAD fitting is complicated by the multiple local minima caused by the zigzag-discontinuities of the aliasing operator. An efficient two-step VAD algorithm is thus developed in this paper to find the global minimum in properly transformed subspaces of the VAD wind parameters. The algorithm is then extended into a three-step volume velocity processing (VVP) method to estimate the vertical profile of horizontal winds from each volume of radar radial-velocity scans. Examples are presented to illustrate the capability and robustness of the method.

Xu, Q., L. Wei, W. Gu, J. Gong, Q. Zhao, 2010: A 3.5-Dimensional Variational Method for Doppler Radar Data Assimilation and Its Application to Phased-Array Radar Observations. Advances in Meteorology, 2010, 61-74.

A 3.5-dimensional variational method is developed for Doppler radar data assimilation. In this method, incremental analyses are performed in three steps to update the model state upon the background state provided by the model prediction. First, radar radial-velocity observations from three consecutive volume scans are analyzed on the model grid. The analyzed radial-velocity fields are then used in step 2 to produce incremental analyses for the vector velocity fields at two time levels between the three volume scans. The analyzed vector velocity fields are used in step 3 to produce incremental analyses for the thermodynamic fields at the central time level accompanied by the adjustments in water vapor and hydrometeor mixing ratios based on radar reflectivity observations. The finite element B-spline representations and recursive filter are used to reduce the dimension of the analysis space and enhance the computational efficiency. The method is applied to a squall line case observed by the phased-array radar with rapid volume scans at the National Weather Radar Testbed and is shown to be effective in assimilating the phased-array radar observations and improve the prediction of the subsequent evolution of the squall line.

Xu, Q., 2010: Modal and Nonmodal Growths of Symmetric Perturbations in Unbounded Domain. Journal of the Atmospheric Sciences, 67, 1996-2017.

Xu, Q., K. Nai, P. Zhang, S. Liu, D. Parrish, 2009: A new dealiasing method for Doppler velocity data quality control. Preprints, 34rd Conference on Radar Meteorology, Williamsburg, VA, USA, Amer. Meteor. Soc., CD-ROM, P9.6.

Available online at http://ams.confex.com/ams/34Radar/techprogram/paper_155947.htm.

Xu, Q., K. Nai, L. Wei, P. Zhang, S. Liu, D. Parrish, 2011: A VAD-based dealiasing method for radar velocity data quality control. Journal of Atmospheric and Oceanic Technology, 28, 50-62.

This paper describes a new VAD-based dealiasing method developed for automated radar radial-velocity data quality control to satisfy the high quality standard and efficiency required by operational radar data assimilation. The method is built on an alias-robust velocity azimuth display (AR-VAD) analysis. It upgrades and simplifies the previous three-step dealiasing method in three major aspects. First, the AR-VAD is used with sufficiently stringent threshold conditions in place of the original modified VAD for the preliminary reference check to produce alias-free seed data in the first step. Second, the AR-VAD is more accurate than the traditional VAD for the refined reference check in the original second step, so the original second step becomes unnecessary and is removed. Third, a block-to-point continuity check procedure is developed, in place of the point-to-point continuity check in the original third step, to enhance the use of available seed data in a properly enlarged block area around each flagged data point that is being checked with multiple threshold conditions to avoid false dealiasing. The new method has been tested extensively with aliased radial-velocity data collected under various weather conditions, including hurricane high-wind conditions. The robustness of the new method is exemplified by the result tested with a hurricane case. The limitations of the new method and possible improvements are discussed.

Xu, Q., 2011: Measuring information content from observations for data assimilation: Spectral formulations and their implications to observational data compression. Tellus, 63A, 793-804.

The previous singular-value formulations for measuring information content from observations are transformed into spectral forms in the wavenumber space for univariate analyses of uniformly distributed observations. The transformed spectral formulations exhibit the following advantages over their counterpart singular-value formulations: (i) The information contents from densely distributed observations can be calculated very efficiently even if the background and observation space dimensions become both too large to compute by using the singular-value formulations. (ii) The information contents and their asymptotic properties can be analyzed explicitly for each wavenumber. (iii) Super-observations can be not only constructed by a truncated spectral expansion of the original observations with zero or minimum loss of information but also explicitly related to the original observations in the physical space. The spectral formulations reveal that (i) uniformly thinning densely distributed observations will always cause a loss of information and (ii) compressing densely distributed observations into properly coarsened super-observations by local averaging may cause no loss of information under certain circumstances.

Xu, Q., 2011: Completeness of Normal Modes for Symmetric Perturbations in Vertically Bounded Domain. J. Met. Soc. Japan, 89, 389-397.

Perturbations generated by symmetric instability can be characterized, in terms of growing normal modes, by slantwise vertical motion bands similar to those observed in frontal rainbands. Nonmodal growths of symmetric perturbations, characterized also by slantwise vertical motion bands, can be produced by linear combinations of normal modes even before the basic state becomes symmetrically unstable to generate growing modes. In this paper, normal modes for nonhydrostatic symmetric perturbations in a vertically bounded domain are revisited and constructed by free modes obtained in unbounded domain. The constructed modes form a complete set in the full-solution space and thus can construct any admissible solutions to further explore nonmodal growths of symmetric perturbations in the vertically bounded domain beyond previous studies.

Xu, Q., J. Cao, S. Gao, 2011: Computing streamfunction and velocity potential in a limited domain. Part I: Theory and integral formulae. Adv. Atmos. Sci., 28, 1433-1444.

The non-uniqueness of solution and compatibility between the coupled boundary conditions in computing velocity potential and streamfunction from horizontal velocity in a limited domain of arbitrary shape are revisited theoretically with rigorous mathematic treatments. Classic integral formulas and their variants are used to formulate solutions for the coupled problems.
In the absence of data holes, the total solution is the sum of two integral solutions. One is the internally induced solution produced purely and uniquely by the domain internal divergence and vorticity, and its two components (velocity potential and streamfunction) can be constructed by applying Green's function for Poisson equation in unbounded domain to the divergence and vorticity inside the domain. The other is the externally induced solution produced purely but non-uniquely by the domain external divergence and vorticity, and the non-uniqueness is caused by the harmonic nature of the solution and the unknown divergence and vorticity distributions outside the domain. By setting either the velocity potential (or streamfunction) component to zero, the other component of the externally induced solution can be expressed by the imaginary (or real) part of the Cauchy integral constructed using the coupled boundary conditions and solvability conditions that exclude the internally induced solution. The streamfunction (or velocity potential) for the externally induced solution can also be expressed by the boundary integral of a double-layer (or single-layer) density function. In the presence of data holes, the total solution includes a data-hole--induced solution in addition to the above internally and externally induced solutions.

Xu, Q., L. Wei, 2011: Measuring information content from observations for data assimilation: Utilities of spectral formulations for radar data compression. Tellus, 63A, 1014-1027.

Utilities of the spectral formulations for measuring information content from observations are explored and demonstrated with real radar data. It is shown that the spectral formulations can be used (i) to precisely compute the information contents from one-dimensional radar data uniformly distributed along the radar beam, (ii) to approximately estimate the information contents from two-dimensional radar observations non-uniformly distributed on the conical surface of radar scan, and thus (iii) to estimate the information losses caused by super-observations generated by local averaging with a series of successively coarsened resolutions to find an optimally coarsened resolution for radar data compression with zero or near-zero minimal loss of information. The results obtained from the spectral formulations are verified against the results computed accurately but costly from the singular-value formulations. As the background and observation error power spectra can be derived analytically for the above utilities, the spectral formulations are computationally much more efficient and affordable than the singular-value formulations, even and especially when the background space and observation space are both extremely large and too large to be computed by the singular-value formulations.

Xue, M., F. Kong, D. Weber, K. W. Thomas, Y. Wang, K. Brewster, K. K. Droegemeier, J. S. Kain, S. J. Weiss, D. R. Bright, M. S. Wandishin, M. C. Coniglio, J. Du, 2007: CAPS realtime storm-scale ensemble and high-resolution forecasts as part of the NOAA Hazardous Weather Testbed 2007 Spring Experiment.. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 3B.1.

Xue, M., F. Kong, D. B. Weber, K. W. Thomas, Y. Wang, K. Brewster, K. K. Droegemeier, J. S. Kain, S. J. Weiss, D. R. Bright, M. S. Wandishin, M. C. Coniglio, J. Du, 2007: CAPS realtime storm-scale ensemble and high-resolution forecasts as part of the NOAA Hazardous Weather Testbed 2007 Spring Experiment. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 3B.1. [Available from Ming Xue, CAPS, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

As a continuation of past collaborations with the NOAA Hazardous Weather Testbed (HWT), the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma will produce daily 10-member 4-km-resolution ensemble forecasts during the spring of 2007, as contributions to the HWT 2007 Spring Experiment. At the same time, a single 2-km deterministic forecast will be produced over the same domain that covers two thirds of the continental US. The forecasts will start from 2100 UTC and extend to 0600 UTC of the third day for a total length of 33 hours. The experiment will start in mid-April and last for about 2 months.

The CAPS effort in 2007 will use the WRF ARW model and the ensemble will include both initial/boundary condition and physics perturbations. The initial and boundary condition perturbations will come from the NCEP 2100 UTC SREF forecast cycle, with the control-member initial condition coming from the NAM 2100 UTC analysis on the 12 km grid. The physics perturbation members are designed for easy identification of the strengths and weakness of leading microphysics and PBL schemes within WRF.

Selected data fields will be fed directly into the NAWIPS systems in the HWT for use by experimental forecast and evaluation teams in the Spring Experiment. These will be combined with separate deterministic WRF forecasts at 3 km grid spacing, contributed by NCAR and EMC. Additional data fields from the CAPS runs will be posted on the web in realtime for external verification purposes. These include side by side comparisons of 2-km forecast composite reflectivity with the NSSL national reflectivity mosaic at 5-minute intervals and graphical displays of a large array of 2-D fields and ensemble products, including postage stamps and probability maps

Over 1000 CPUs at the Pittsburgh Supercomputing Center (PSC) will be used to produce the forecasts while additional processors at the University of Oklahoma Supercomputing Center for Education and Research (OSCER) will be used for post-processing. A special super-high-speed link capable of 200 MB/s will be set up between PSC and OSCER for data transfer.

Results of realtime forecasts and preliminary retrospective analysis on selected cases will be presented at the conference.

Available online at http://ams.confex.com/ams/pdfpapers/124587.pdf.

Xue, M., F. Kong, K. W. Thomas, J. Gao, Y. Wang, K. Brewster, K. K. Droegemeier, J. S. Kain, S. J. Weiss, D. R. Bright, M. C. Coniglio, J. Du, 2009: CAPS realtime 4 km multi-model convection-allowing ensemble and 1 km convection-resolving forecasts for the NOAA Hazardous Weather Testbed 2009 Spring Experiment. Preprints, 23rd Conference on Weather Analysis and Forecasting/19th Conference on Numerical Weather Prediction, Omaha, NE, USA, Amer. Meteor. Soc., CD-ROM, 16A.2.

Available online at http://ams.confex.com/ams/23WAF19NWP/techprogram/paper_154323.htm.

Xue, M., F. Kong, K. W. Thomas, J. Gao, Y. Wang, K. Brewster, K. K. Droegemeier, J. S. Kain, S. J. Weiss, D. R. Bright, M. C. Coniglio, J. Du, 2008: CAPS realtime storm-scale ensemble and high-resolution forecasts as part of the NOAA Hazardous Weather Testbed 2008 Spring Experiment. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., CD-ROM, 12.2.

Available online at http://ams.confex.com/ams/24SLS/techprogram/paper_142036.htm.

Yeary, M., R. Palmer, M. Xue, T. Y. Yu, G. Zhang, A. Zahrai, J. Crain, Y. Zhang, R. Doviak, Q. Xu, P. Chilson, 2008: Introduction to multi-channel receiver development for the realization of multi-mission capabilities at the National Weather Radar Testbed. Extended Abstracts, 24rd Conference on Interactive Information Processing Systems (IIPS), New Orleans, LA, USA, AMS, 9A.3.

Yeary, M., G. E. Crain, A. Zahrai, T. Yu, R. Palmer, G. Zhang, Y. Zhang, R. J. Doviak, P. Chilson, M. Xue, Q. Xu, 2009: An update on multi-channel receiver development for the realization multi-mission capabilities at the national weather radar testbed. Extended Abstracts, 25th Conference on International Interactive Information and Processing Systems (IIPS) for Meteorology, Oceanography, and Hydrology, Phoenix, AZ, USA, AMS, CD-ROM, 8B.5.

Yeary, M., J. Crain, A. Zahrai, R. Kelley, J. Meier, Y. Zhang, I. Ivic, C. Curtis, R. Palmer, T. Y. Yu, G. Zhang, R. J. Doviak, P. B. Chilson, M. Xue, Q. Xu, 2010: A status report on the RF and digital components of the multi-channel receiver development at the National Weather Radar Testbed. Extended Abstracts, 26th Conference on International Interactive Information and Processing Systems (IIPS) for Meteorology, Oceanography, and Hydrology, Atlanta, GA, USA, AMS, CD-ROM, 14B.3.

Available online at http://ams.confex.com/ams/90annual/techprogram/paper_160298.htm.

Yu, T. Y., A. B. Chalamalasetti, R. J. Doviak, D. S. Zrnic, 2006: Resolution Enhancement Technique using Range Oversampling. Journal of Atmospheric and Oceanic Technology, 23, 228-240.

Yu, T. Y., G. Zhang, A. Chalamalasetti, R. J. Doviak, D. S. Zrnic, 2005: Improve Radar Resolution using Range Oversampling. Preprints, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, AMS, CD-ROM, 4R.4.

Yussouf, N., D. J. Stensrud, 2006: Prediction of near surface variables at independent locations from a bias-corrected ensemble forecasting system. Monthly Weather Review, 134, 3415-3424.

The ability of a multimodel short-range bias-corrected ensemble (BCE) forecasting system, created as part of NOAA’s New England High Resolution Temperature Program during the summer of 2004, to obtain accurate predictions of near-surface variables at independent locations within the model domain is explored. The original BCE approach produces bias-corrected forecasts only at National Weather Service (NWS) observing surface station locations. To extend this approach to obtain bias-corrected forecasts at any given location, an extended BCE technique is developed and applied to the independent observations provided by the Oklahoma Mesonet. First, a Cressman weighting scheme is used to interpolate the bias values of 2-m temperature, 2-m dewpoint temperature, and 10-m wind speeds calculated from the original BCE approach at the NWS observation station locations to the Oklahoma Mesonet locations. These bias values are then added to the raw numerical model forecasts bilinearly interpolated to this same specified location. This process is done for each forecast member within the ensemble and at each forecast time. It is found that the performance of the extended BCE is very competitive with the original BCE approach across the state of Oklahoma. Therefore, a simple postprocessing scheme like the extended BCE system can be used as part of an operational forecasting system to provide reasonably accurate predictions of near surface variables at any location within the model domain.

Yussouf, N., D. J. Stensrud, 2007: Bias-Corrected Short-Range Ensemble Forecasts of Near-Surface Variables during the 2005/06 Cool Season. Weather and Forecasting, 22, 1274-1286.

A postprocessing method initially developed to improve near-surface forecasts from a summertime multimodel short-range ensemble forecasting system is evaluated during the cool season of 2005/06. The method, known as the bias-corrected ensemble (BCE) approach, uses the past complete 12 days of model forecasts and surface observations to remove the mean bias of near-surface variables from each ensemble member for each station location and forecast time. In addition, two other performance-based weighted-average BCE schemes, the exponential smoothing method BCE and the minimum variance estimate BCE, are implemented and evaluated. Values of root-mean-squared error from the 2-m temperature and dewpoint temperature forecasts indicate that the BCE approach outperforms the routinely available Global Forecast System (GFS) model output statistics (MOS) forecasts during the cool season by 9% and 8%, respectively. In contrast, the GFS MOS provides more accurate forecasts of 10-m wind speed than any of the BCE methods. The performance-weighted BCE schemes yield no significant improvement in forecast accuracy for 2-m temperature and 2-m dewpoint temperature when compared with the original BCE, although the weighted BCE schemes are found to improve the forecast accuracy of the 10-m wind speed. The probabilistic forecast guidance provided by the BCE system is found to be more reliable than the raw ensemble forecasts. These results parallel those obtained during the summers of 2002–04 and indicate that the BCE method is a promising and inexpensive statistical postprocessing scheme that could be used in all seasons.

Yussouf, N., D. J. Stensrud, 2008: Reliable Probabilistic Quantitative Precipitation Forecasts from a Short-Range Ensemble Forecasting System during the 2005/06 Cool Season. Monthly Weather Review, 136, 2157-2172.

A simple binning technique developed to produce reliable probabilistic quantitative precipitation forecasts (PQPFs) from a multimodel short-range ensemble forecasting system is evaluated during the cool season of 2005/06. The technique uses forecasts and observations of 3-h accumulated precipitation amounts from the past 12 days to adjust the present day’s 3-h quantitative precipitation forecasts from each ensemble member for each 3-h forecast period. Results indicate that the PQPFs obtained from this simple binning technique are significantly more reliable than the raw (original) ensemble forecast probabilities. Brier skill scores and areas under the relative operating characteristic curve also reveal that this technique yields skillful probabilistic forecasts of rainfall amounts during the cool season. This holds true for accumulation periods of up to 48 h. The results obtained from this wintertime experiment parallel those obtained during the summer of 2004. In an attempt to reduce the effects of a small sample size on two-dimensional probability maps, the simple binning technique is modified by implementing 5- and 9-point smoothing schemes on the adjusted precipitation forecasts. Results indicate that the smoothed ensemble probabilities remain an improvement over the raw (original) ensemble forecast probabilities, although the smoothed probabilities are not as reliable as the unsmoothed adjusted probabilities. The skill of the PQPFs also is increased as the ensemble is expanded from 16 to 22 members during the period of study. These results reveal that simple postprocessing techniques have the potential to provide greatly improved probabilistic guidance of rainfall events for all seasons of the year.

Yussouf, N., D. J. Stensrud, 2008: Impact of high temporal frequency radar data assimilation on storm-scale NWP model simulations. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., 9B.1. [Available from Nusrat Yussouf, 120 David L. Boren Blvd., Norman, OK, USA, 73072.]

Radial-velocity and reflectivity observations from Doppler radars can provide important information for initializing numerical storm-scale prediction models and in diagnosing the evolution of severe weather events like thunderstorms and tornadoes. Recent research indicates that the assimilation of Doppler radar data using the Ensemble Kalman Filter (EnKF) approach generates good estimates of storm structure. While the conventional Doppler radar takes 4-5 minutes to scan a thunderstorm, the new and emerging Phased Array Radar (PAR) rapid and adaptive scanning technology can scan the same storm in less than a minute and can enhance the scanning angles in real time to get a better depiction of the storm top. Thus, in an effort to explore the impact of high temporal frequency PAR observations in storm assimilation, Observing System Simulation Experiments (OSSEs) are designed using the EnKF as a method for initializing storm-scale numerical forecast models.

Several different OSSEs are conducted with radial-velocity and reflectivity observations constructed from simulated supercells in native radar coordinates using a realistic volume averaging technique. Two sets of experiment are run for each OSSE. One experiment assimilates the simulated Doppler radar observations while the other experiment assimilates the high temporal frequency PAR observations. Results obtained are compared to document the value of new PAR observations to the creation of improved storm analyses and short-range ensemble forecasts.

Available online at http://ams.confex.com/ams/pdfpapers/141555.pdf.

Yussouf, N., D. J. Stensrud, 2010: Impact of Phased-Array Radar Observations over a Short Assimilation Period: Observing System Simulation Experiments Using an Ensemble Kalman Filter. Monthly Weather Review, 138, 517-538.

The conventional Weather Surveillance Radar-1988 Doppler (WSR-88D) scans a given weather phenomenon in approximately 5 min, and past results suggest that it takes 30–60 min to establish a storm into a model assimilating these data using an ensemble Kalman filter (EnKF) data assimilation technique. Severe weather events, however, can develop and evolve very rapidly. Therefore, assimilating observations for a 30–60-min period prior to the availability of accurate analyses may not be feasible in an operational setting. A shorter assimilation period also is desired if forecasts are produced to increase the warning lead time. With the advent of the emerging phased-array radar (PAR) technology, it is now possible to scan the same weather phenomenon in less than 1 min. Therefore, it is of interest to see if the faster scanning rate of PAR can yield improvements in storm-scale analyses and forecasts from assimilating over a shorter period of time. Observing system simulation experiments are conducted to evaluate the ability to quickly initialize a storm into a numerical model using PAR data in place of WSR-88D data. Synthetic PAR and WSR-88D observations of a splitting supercell storm are created from a storm-scale model run using a realistic volume-averaging technique in native radar coordinates. These synthetic reflectivity and radial velocity observations are assimilated into the same storm-scale model over a 15-min period using an EnKF data assimilation technique followed by a 50-min ensemble forecast. Results indicate that assimilating PAR observations at 1-min intervals over a short 15-min period yields significantly better analyses and ensemble forecasts than those produced using WSR-88D observations. Additional experiments are conducted in which the adaptive scanning capability of PAR is utilized for thunderstorms that are either very close to or far away from the radar location. Results show that the adaptive scanning capability improves the analyses and forecasts when compared with the nonadaptive PAR data. These results highlight the potential for flexible rapid-scanning PAR observations to help to quickly and accurately initialize storms into numerical models yielding improved storm-scale analyses and very short range forecasts.

Yussouf, N., D. J. Stensrud, 2012: Comparison of Single-Parameter and Multiparameter Ensembles for Assimilation of Radar Observations Using the Ensemble Kalman Filter.. Monthly Weather Review, 140, 562-586.

Observational studies indicate that the densities and intercept parameters of hydrometeor distributions can vary widely among storms and even within a single storm. Therefore, assuming a fixed set of microphysical parameters within a given microphysics scheme can lead to significant errors in the forecasts of storms. To explore the impact of variations in microphysical parameters, Observing System Simulation Experiments are conducted based on both perfect- and imperfect-model assumptions. Two sets of ensembles are designed using either fixed or variable parameters within the same single-moment microphysics scheme. The synthetic radar observations of a splitting supercell thunderstorm are assimilated into the ensembles over a 30-min period using an ensemble Kalman filter data assimilation technique followed by 1-h ensemble forecasts. Results indicate that in the presence of a model error, a multiparameter ensemble with a combination of different hydrometeor density and intercept parameters leads to improved analyses and forecasts and better captures the truth within the forecast envelope compared to single-parameter ensemble experiments with a single, constant, inaccurate hydrometeor intercept and density parameters. This conclusion holds when examining the general storm structure, the intensity of midlevel rotation, surface cold pool strength, and the extreme values of the model fields that are most helpful in determining and identifying potential hazards. Under a perfect-model assumption, the single- and multiparameter ensembles perform similarly as model error does not play a role in these experiments. This study highlights the potential for using a variety of realistic microphysical parameters across the ensemble members in improving the analyses and very short-range forecasts of severe weather events.

Zhang, P., S. Liu, Q. Xu, Lulin Song, 2005: Storm targeted radar wind retrieval system. 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, P8R1.

Zhang, P., S. Liu, Q. Xu, 2005: Quality control of Doppler velocities contaminated by migrating birds. Part I: Feature extraction and quality control parameters. Journal of Atmospheric and Oceanic Technology, 22, 1105-1113.

Zhang, S. W., C. J. Qiu, Q. Xu, 2005: Reply. Journal of Applied Meteorology, 44, 551-552.

Zhang, G., Q. Cao, M. Xue, P. Chilson, M. Morris, R. Palmer, J. Brotzke, T. Schuur, E. Brandes, K. Ikeda, A. Ryzhkov, D. Zrnic, E. Jessup, 2008: A field experiment to study rain microphysics using video disdrometers and polarimetric S and X-band radars. Preprints, Symposium on Recent Developments in Atmospheric Applications of Radar and Lidar, New Orleans, LA, USA, American Meteorological Society, P2.23.

Zhang, J., K. Howard, X. Xu, 2008: A warm season radar QPE algorithm using adaptive Z-R relationships. Proc. World Environmental and Water Resources Congress 2008, Honolulu, HI, USA, Amer. Soc. Civil Engineers, CD-ROM, 420.pdf.

Zhang, J., C. Langston, K. Howard, B. Clarke, 2006: Gap-filling in 3D radar mosaic analysis using vertical profile of reflectivity. Preprints, The 12th Conference on Aviation, Range, and Aerospace Meteorology, Atlanta, GA, USA, Amer. Meteor. Soc., CD-ROM, P1.9.

Zhang, G., S. Luchs, A. Ryzhkov, M. Xue, L. Ryzhkova, Q. Cao, 2011: Winter precipitation microphysics characterized by polarimetric radar and video disdrometer observations in central Oklahoma. Journal of Applied Meteorology and Climatology, 50, 1558-1570.

The study of precipitation in different phases is important to understanding the physical processes that occur in storms, as well as to improving their representation in numerical weather prediction models. A 2D video disdrometer was deployed about 30 km from a polarimetric weather radar in Norman, Oklahoma, (KOUN) to observe winter precipitation events during the 2006/07 winter season. These events contained periods of rain, snow, and mixed-phase precipitation. Five-minute particle size distributions were generated from the disdrometer data and fitted to a gamma distribution; polarimetric radar variables were also calculated for comparison with KOUN data. It is found that snow density adjustment improves the comparison substantially, indicating the importance of accounting for the density variability in representing model microphysics.

Zhao, Q., J. Cook, Q. Xu, P. Harasti, 2005: Improving very-short-term storm predictions by assimilating radar data into a mesoscale NWP model. 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, XXXX.

Zhao, Q., J. Cook, Q. Xu, P. Harasti, 2006: Using radar wind observations to improve mesoscale numerical weather prediction. Weather and Forecasting, 21, 502-522.

Zhao, Q., J. Cook, Q. Xu, P. Harasti, 2008: Improving short-term storm predictions by assimilating both radar radial-wind and reflectivity observations.. Weather and Forecasting, 23, 373-391.

Ziegler, C. L., M. S. Buban, E. N. Rasmussen, 2007: A Lagrangian Objective Analysis Technique for Assimilating In Situ Observations with Multiple-Radar-Derived Airflow. Monthly Weather Review, 135, 2417-2442.

A new Lagrangian analysis technique is developed to assimilate in situ boundary layer measurements using multi-Doppler-derived wind fields, providing output fields of water vapor mixing ratio, potential temperature, and virtual potential temperature from which the lifting condensation level (LCL) and relative humidity (RH) fields are derived. The Lagrangian analysis employs a continuity principle to bidirectionally distribute observed values of conservative variables with the 3D, evolving boundary layer airflow, followed by temporal and spatial interpolation to an analysis grid. Cloud is inferred at any grid point whose height z > zLCL or equivalently where RH ≥ 100%. Lagrangian analysis of the cumulus field is placed in the context of gridded analyses of visible satellite imagery and photogrammetric cloud-base area analyses. Brief illustrative examples of boundary layer morphology derived with the Lagrangian analysis are presented based on data collected during the International H2O Project (IHOP): 1) a dryline on 22 May 2002; 2) a cold-frontal–dryline “triple point” intersection on 24 May 2002. The Lagrangian analysis preserves the sharp thermal gradients across the cold front and drylines and reveals the presence of undulations and plumes of water vapor mixing ratio and virtual potential temperature associated with deep penetrative updraft cells and convective roll circulations. Derived cloud fields are consistent with satellite-inferred cloud cover and cloud-base locations.

Ziegler, C. L., E. N. Rasmussen, M. S. Buban, Y. P. Richardson, L. J. Miller, R. M. Rabin, 2007: The "Triple Point" on 24 May 2002 during IHOP. Part II: Ground-Radar and In Situ Boundary Layer Analysis of Cumulus Development and Convection Initiation. Monthly Weather Review, 135, 2443-2472.

Cumulus formation and convection initiation are examined near a cold front–dryline “triple point” intersection on 24 May 2002 during the International H2O Project (IHOP). A new Lagrangian objective analysis technique assimilates in situ measurements using time-dependent Doppler-derived 3D wind fields, providing output 3D fields of water vapor mixing ratio, virtual potential temperature, and lifted condensation level (LCL) and water-saturated (i.e., cloud) volumes on a subdomain of the radar analysis grid. The radar and Lagrangian analyses reveal the presence of along-wind (i.e., longitudinal) and cross-wind (i.e., transverse) roll circulations in the boundary layer (BL). A remarkable finding of the evolving radar analyses is the apparent persistence of both transverse rolls and individual updraft, vertical vorticity, and reflectivity cores for periods of up to 30 min or more while moving approximately with the local BL wind. Satellite cloud images and single-camera ground photogrammetry imply that clouds tend to develop either over or on the downwind edge of BL updrafts, with a tendency for clouds to elongate and dissipate in the downwind direction relative to cloud layer winds due to weakening updrafts and mixing with drier overlying air. The Lagrangian and radar wind analyses support a parcel continuity principle for cumulus formation, which requires that rising moist air parcels achieve their LCL before moving laterally out of the updraft. Cumuli form within penetrative updrafts in the elevated residual layer (ERL) overlying the moist BL east of the triple point, but remain capped by a convection inhibition (CIN)-bearing layer above the ERL. Dropsonde data suggest the existence of a convergence line about 80 km east of the triple point where deep lifting of BL moisture and locally reduced CIN together support convection initiation.

Ziegler, C. L., E. N. Rasmussen, M. Buban, Y. Richardson, L. J. Miller, R. Rabin, 2005: The boundary layer cumulus formation process near a cold frontal-dryline intersection on 24 May 2002 during IHOP. Preprints, 11th Conference on Mesoscale Processes, Albuquerque, NM, USA, AMS, J6J.2.

Ziegler, C. L., E. Mansell, J. Straka, D. MacGorman, D. Burgess, 2007: Impact of varying inversion strength on the electrification, lightning, kinematics, and microphysics in a simulated supercell storm. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, International Commission on Atmospheric Electricity, 225-228.

Ziegler, C. L., E. R. Mansell, J. M. Straka, D. R. MacGorman, D. W. Burgess, 2008: Impact of Spatially Varying Inversion Strength on the Evolution of a Simulated Supercell Storm.. Extended Abstracts, 24th Conference on Severe Local Storms, Savannah, GA, USA, American Meteorological Society, P10.10.

Ziegler, C. L., K. Kuhlman, M. Biggerstaff, D. Betten, L. Wicker, E. Mansell, D. MacGorman, 2008: Evolution of low-level rotation in the tornadic 29 May 2004 Geary, Oklahoma supercell storm. Extended Abstracts, 24th Conference on Severe Local Storms, Savannah, GA, USA, AMS, 2.2.

Two mobile C-band Doppler SMART radars sampled a high-precipitation, tornadic supercell storm on 29 May 2004 during its severe, right-moving phase. Bulk parameters of the storm’s near-environment were obtained from approximately hourly, storm-following mobile GPS advanced upper-air sounding system (MGAUS) profiles obtained within the storm’s inflow extending from its initiation stage through the time of maximum low-level rotation in central Oklahoma. Analysis of the high-resolution, dual-Doppler three-dimensional airflow focuses on identifying downdraft source regions and estimating vorticity dynamical processes that contribute to the development of the low-level mesocyclonic and tornado-cyclonic circulations.

During the storm’s most intense phase, a storm-scale rear-flank downdraft boundary (RFDB) intersected the conventional forward flank downdraft boundary (FFDB) within the wrapping inflow to the intensifying low-level mesocyclone. The combined dataset facilitates preliminary testing of the hypothesis that the low-level mesocyclone is intensified via the classical mechanism of solenoidal (horizontal streamwise) vorticity generation followed by tilting and stretching with contributions from both the RFDB and FFDB. The evolution of the low-level angular momentum field will also be examined as a preliminary test of the alternate hypothesis that RFD development combined with strong stratification of horizontal angular momentum may combine to trigger a corner-flow collapse process leading to low-level mesocyclogenesis. This case illustrates the likely hypothesis testing procedures for other supercell storms sampled by the SMART radars during the upcoming VORTEX2 field project.

Ziegler, C. L., E. R. Mansell, E. C. Bruning, 2010: Impact of varying CCN concentration on the precipitation process in a simulated convective storm. Extended Abstracts, 13th Conference on Cloud Physics, Portland, OR, USA, American Meteorological Society, JP3.17.

The effects of the concentration of cloud condensation nuclei (CCN) on cloud microphysics have long been recognized, though the impact of CCN on the precipitation process in convective storms has been relatively unexplored. In the present study, the impact of varying CCN concentration on the microphysical structure and evolution of a small multicell storm is simulated with NSSL's 3-dimensional cloud model (COMMAS). The 2-moment microphysics scheme used for this study predicts the mass mixing ratio and number concentration of cloud droplets, rain, ice crystals, snow, graupel, and hail. CCN concentration is predicted as a single-category, monodisperse size spectrum approximating small aerosols. Bulk graupel and hail particle densities are also predicted as functions of rime layer density. Rime density in turn is a function of droplet size (affected by CCN concentration) and impact speed. Particle density (graupel and hail) is also used as a roughness parameter to scale the drag coefficient in the expression for particle fallspeed. The prediction of hydrometeor number concentration is particularly critical to the resolution of secondary ice nucleation at higher temperatures (-5 < T < -20 C) in the mixed phase updraft region, where ice crystals may be produced both by rime fracturing (Hallett–Mossop process) and by splintering of freezing drops in addition to a range of primary nucleation mechanisms. The prediction of cloud droplet and rain drop concentration and mass and their evolution proceeds through condensation growth, quasi-stochastic coalescence, and vertical transport to force the production of graupel embryos via drop freezing (Bigg freezing and crystal contact nucleation).

Model sensitivity tests with a range of ambient CCN concentrations (50 to 2000 per cubic cm) control the mean droplet size at cloud base, thereby modulating drop growth via condensation-coalescence in environments effectively ranging from maritime to continental. Higher CCN concentrations reduce the collision-coalescence formation of rain/drizzle, gradually increasing the proportion of precipitation mass produced by a graupel-based, cold-cloud riming process relative to the warm rain process. Even at the highest CCN concentrations, the primary process of simulated graupel initiation is via drop freezing. Even in the event of high CCN, the vapor supply in the updraft remains sufficient for droplets to eventually grow large enough via condensation to accelerate drop coalescence growth. The time-integrated volume containing graupel at heights above the freezing level increases monotonically with increasing CCN according to a power law relationship.

Precipitation in the simulated storm initiates as raindrops via stochastic collision-coalescence in regions of high cloud water content just below the freezing level. However as expected, formation of significant rain mixing ratios and simulated radar echo are delayed to later times and higher altitudes as CCN concentration is increased. Raindrops lifted in updraft begin freezing at temperatures around -10 deg. C to form graupel. The simulated time-height reflectivity, graupel mass, rain mass, and updraft volume all show systematic variations in their evolutions as base CCN concentration increases. Updraft volume tends to show three maxima at increasing altitudes of 2-3 km, 6-7 km, and 8-11 km at times of about 25-30 min, 40-55 min and 55-65 min in the simulation. Peak integrated rain mass above the freezing level is maximized at CCN concentration of about 500 cm-3, whereas maximum integrated graupel mass tends to increase monotonically with increasing CCN concentration. Average graupel density tends to decrease with increasing CCN concentration above 500 cm-3, as smaller droplets and lower graupel fall speeds lead to lower-density rime formation. As a by-product of the variation of simulated cloud and precipitation content with CCN, additional cloud simulations in which optional electrification mechanisms are activated manifest a sensitivity of microphysically-based charge separation and lightning production to CCN changes.

Available online at http://ams.confex.com/ams/13CldPhy13AtRad/techprogram/paper_171866.htm.

Ziegler, C. L., E. R. Mansell, J. M. Straka, D. R. MacGorman, D. W. Burgess, 2010: The impact of spatial variations of low-level stability on the life cycle of a simulated supercell storm. Monthly Weather Review, 138, 1738-1766.

This study reports on the dynamical evolution of simulated, long-lived right-moving supercell storms in a high-CAPE, strongly sheared mesoscale environment, which initiate in a weakly capped region and subsequently move into a cold boundary layer (BL) and inversion region before dissipating. The storm simulations realistically approximate the main morphological features and evolution of the 22 May 1981 Binger, Oklahoma, supercell storm by employing time-varying inflow lateral boundary conditions for the storm relative moving grid, which in turn are prescribed from a parent, fixed steady-state mesoscale analysis to approximate the observed inversion region to the east of the dryline on that day. A series of full life cycle storm simulations have been performed in which the magnitude of boundary layer coldness and the convective inhibition are varied to examine the ability of the storm to regenerate and sustain its main updraft as it moves into environments with increasing convective stability. The analysis of the simulations employs an empirical expression for the theoretical speed of the right-forward-flank outflow boundary relative to the ambient, low-level storm inflow that is consistent with simulated cold-pool boundary movement. The theoretical outflow boundary speed in the direction opposite to the ambient flow increases with an increasing cold-pool temperature deficit relative to the ambient BL temperature, and it decreases as ambient wind speed increases. The right-moving, classic (CL) phase of the simulated supercells is supported by increasing precipitation content and a stronger cold pool, which increases the right-moving cold-pool boundary speed against the constant ambient BL winds. The subsequent decrease of the ambient BL temperature with eastward storm movement decreases the cold-pool temperature deficit and reduces the outflow boundary speed against the ambient winds, progressing through a state of stagnation to an ultimate retrogression of the outflow boundary in the direction of the ambient flow. Onset of a transient, left-moving low-precipitation (LP) phase is initiated as the storm redevelops on the retrograding outflow boundary. The left-moving LP storm induces compensating downward motions in the inversion layer that desiccates the inflow, elevates the cloudy updraft parcel level of free convection (LFC), and leads to the final storm decay. The results demonstrate that inversion-region simulations support isolated, long-lived supercells. Both the degree of stratification and the coldness of the ambient BL regulate the cold-pool intensity and the strength and capacity of the outflow boundary to lift BL air through the LFC and thus regenerate convection, resulting in variation of supercell duration in the inversion region of approximately 1–2 h. In contrast, horizontally homogeneous conditions lacking an inversion region result in the development of secondary convection from the initial isolated supercell, followed by rapid upscale growth after 3 h to form a long-lived mesoscale convective system.

Ziegler, C., L. Wicker, D. Betten, M. Biggerstaff, E. Mansell, K. Kulman, D. MacGorman, 2009: Evolution of Downdraft thermodynamics and low-level rotation in the 29 May 2004 Geary, OK USA Supercell Storm.. Preprints, 5th European Conference on Severe Storms, Landshut, Germany, European Severe Storm Laboratory (ESSL), 29-30.

Available online at http://www.essl.org/ECSS/2009/preprints/O02-6-ziegler.pdf.

Ziegler, C. L., M. I. Biggerstaff, L. J. Wicker, D. W. Burgess, E. R. Mansell, C. S. Schwarz, P. Markowski, Y. P. Richardson, C. C. Weiss, 2010: Storm structure and decay process of the 9 June 2009 Greensburg, KS supercell during VORTEX2. Extended Abstracts, 25th Conference on Severe Local Storms, Denver, CO, USA, AMS, 7A.2.

Zipser, E. J., C. H. Twohy, S. C. Tsay, K. L. Thornhill, S. Tanelli, R. Ross, T. N. Krishnamurti, Q. Ji, G. Jenkins, S. Ismail, N. C. Hsu, R. Hood, G. M. Heymsfield, A. Heymsfield, J. Halvorson, H. M. Goodman, R. Ferrare, J. P. Dunion, M. Douglas, R. Cifelli, G. Chen, E. V. Browell, B. Anderson, 2009: The Saharan Air Layer and the Fate of African Easterly Waves - NASA's AMMA 2006 Field Study of Tropical Cyclogenesis. Bulletin of the American Meteorological Society, 90, 1137-1156.

In 2006, NASA led a field campaign to investigate the factors that control the fate of African easterly waves (AEWs) moving westward into the tropical Atlantic Ocean. Aircraft and surface-based equipment were based on Cape Verde's islands, helping to fill some of the data void between Africa and the Caribbean. Taking advantage of the international African Monsoon Multidisciplinary Analysis (AMMA) program over the continent, the NASA–AMMA (NAMMA) program used enhanced upstream data, whereas NOAA aircraft farther west in the Atlantic studied several of the storms downstream. Seven AEWs were studied during AMMA, with at least two becoming tropical cyclones. Some of the waves that did not develop while being sampled near Cape Verde likely intensified in the central Atlantic instead. NAMMA observations were able to distinguish between the large-scale wave structure and the smaller-scale vorticity maxima that often form within the waves. A special complication of the east Atlantic environment is the Saharan air layer (SAL), which frequently accompanies the AEWs and may introduce dry air and heavy aerosol loading into the convective storm systems in the AEWs. One of the main achievements of NAMMA was the acquisition of a database of remote sensing and in situ observations of the properties of the SAL, enabling dynamic models and satellite retrieval algorithms to be evaluated against high-quality real data. Ongoing research with this database will help determine how the SAL influences cloud micro-physics and perhaps also tropical cyclogenesis, as well as the more general question of recognizing the properties of small-scale vorticity maxima within tropical waves that are more likely to become tropical cyclones.