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.

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., K. L. Elmore, 2005: Objective verification of high-resolution WRF forecasts during 2005 NSSL/SPC Spring Program. Preprints, 21st Conference on Weather Analysis and Forecasting/17th Conference on Numerical Weather Prediction., Durham, NC, USA, American Meteorologocal Society, 11B.4. [Available from Michael Baldwin, 1313 Halley Circle, Norman, OK, USA, 73069.]

Forecast output from several versions of the WRF model will be evaluated during the 2005 NSSL/SPC Spring Program. These include a ~4km grid-spacing version of the WRF-NMM run at NCEP, a ~4km version of WRF-ARW run at NCAR, and a ~2km version of WRF-ARW run by CAPS at PSC. This output will be evaluated subjectively in real-time by teams of operational forecasters and researchers (see Kain et al. 2005, 21st WAF/17th NWP conf). In addition, several objective verification techniques will be applied to these forecasts, in particular, predicted and observed composite radar reflectivities will be compared. Object-oriented techniques will be used to compare the forecast and observed characteristics of a variety of rainfall systems. Other statistical techniques will be applied in order to measure biases in the forecast fields, structure, etc. This paper will report on ongoing research related to meaningful, objective verification of forecasts that contain realistic, high-resolution detail.

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.

Banacos, P. C., D. M. Schultz, 2005: The use of moisture flux convergence in forecasting convective initiation: Historical and operational perspectives. Weather and Forecasting, 20, 351-366.

Moisture flux convergence (MFC) is a term in the conservation of water vapor equation and was first calculated in the 1950s and 1960s as a vertically integrated quantity to predict rainfall associated with synoptic-scale systems. Vertically integrated MFC was also incorporated into the Kuo cumulus parameterization scheme for the Tropics. MFC was eventually suggested for use in forecasting convective initiation in the midlatitudes in 1970, but practical MFC usage quickly evolved to include only surface data, owing to the higher spatial and temporal resolution of surface observations. Since then, surface MFC has been widely applied as a short-term (0-3 h) prognostic quantity for forecasting convective initiation, with an emphasis on determining the favorable spatial location(s) for such development. A scale analysis shows that surface MFC is directly proportional to the horizontal mass convergence field, allowing MFC to be highly effective in highlighting mesoscale boundaries between different air masses near the earth's surface that can be resolved by surface data and appropriate grid spacing in gridded analyses and numerical models. However, the effectiveness of boundaries in generating deep moist convection is influenced by many factors, including the depth of the vertical circulation along the boundary and the presence of convective available potential energy (CAPE) and convective inhibition (CIN) near the boundary. Moreover, lower- and upper-tropospheric jets, frontogenesis, and other forcing mechanisms may produce horizontal mass convergence above the surface, providing the necessary lift to bring elevated parcels to their level of free convection without connection to the boundary layer. Case examples elucidate these points as a context for applying horizontal mass convergence for convective initiation. Because horizontal mass convergence is a more appropriate diagnostic in an ingredients-based methodology for forecasting convective initiation, its use is recommended over MFC.

Barnes, L. R., E. C. Gruntfest, M. H. Hayden, D. M. Schultz, C. Benight, 2007: False alarms and close calls: A conceptual model of warning accuracy. Weather and Forecasting, 22, 1140-1147.

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.

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. Atmospheic 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.

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.

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.

Bruning, E., W. D. Rust, D. MacGorman, T. Schuur, J. Straka, P. Krehbiel, W. Rison, T. Hamlin, 2005: Polarimetric radar and electrical structure of a multicell storm. Preprints, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, P14R.9.

Bruning, E. C., W. D. Rust, T. J. Schuur, D. R. MacGorman, P. R. Krehbiel, W. Rison, 2007: Electrical and Polarimetric Radar Observations of a Multicell Storm in TELEX. Monthly Weather Review, 135, 2525-2544.

On 28-29 June 2004 a multicellular thunderstorm west of Oklahoma City was probed as part of the Thunderstorm Electrification and Lightning Experiment (TELEX) field program. This study makes use of radar observations from the KOUN polarimetric WSR-88D, threedimensional lightning mapping data from the Oklahoma Lightning Mapping Array (LMA), and balloon-borne vector electric field meter (EFM) measurements. The storm had a low flash rate (30 flashes in 40 min). Four charge regions were inferred from a combination of LMA and EFM data. Lower positive charge near 4 km and mid-level negative charge from 4.5–6 km MSL (0 to -6.5°C) were generated in and adjacent to a vigorous updraft pulse. Further mid-level negative charge from 4.5–6 km MSL and upper positive charge from 6–8 km (-6.5 to -19°C) were generated later in quantity sufficient to initiate lightning as the updraft decayed. A negative screening layer was present near storm top (8.5 km MSL, -25°C). Initial lightning flashes were between lower positive and mid-level negative charge and started occurring shortly after a cell began lofting hydrometeors into the mixed phase region, where graupel was formed. A leader from the storm's first flash avoided a region where polarimetric radar suggested wet growth and the resultant absence of non-inductive charging of those hydrometeors. Initiation locations of later flashes that propagated into upper positive charge tracked the descending location of a polarimetric signature of graupel. As the storm decayed, electric fields greater than 160 kV m-1 exceeded the minimum threshold for lightning initiation suggested by the hypothesized runaway breakdown process at 5.5 km MSL, but lightning did not occur. The small spatial extent (≈100 m) of the large electric field may not have been sufficient to allow runaway breakdown to fully develop and initiate lightning.

Bruning, E., W. D. Rust, D. R. MacGorman, M. I. Biggerstaff, P. Krehbiel, 2008: Lightning mapping data as a tool for assessing storm structure and evolution. Proc. 3rd Conference on the Meteorological Applications of Lightning Data, AMS Annual Meeting, New Orleans, LA, New Orleans, LA, USA, American Meteorological Society, 8.1A.

Bruning, E. C., W. D. Rust, D. R. MacGorman, T. J. Schuur, P. R. Krehbiel, W. Rison, 2007: Temporal and Spatial Structure of Storm Charge and Kinematics in the 26 May 2004 Supercell Storm During TELEX. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, International Commission on Atmospheric Electricity, 229-232. [Available from 1313 Halley Circle, 1313 Halley Circle, Norman, OK, USA, 73069.]

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.

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.

Cheong, B., R. Palmer, C. Curtis, K. Hondl, P. Heinselman, D. Zrnic, D. Forsyth, R. Murnan, R. Reed, R. Vogt, M. Foster, 2007: Real-time implementation of refractivity retrieval: Partnership between the University of Oklahoma, National Severe Storms Laboratory, and the Radar Operations Center. Preprints, 33rd Conference on Interactive Information and Processing Systems, San Antonio, TX, USA, American Meteorological Society, CD-ROM, P8B.8.

High-resolution, near-surface refractivity measurements have the potential of becoming an important tool for operational forecasting and general scientific studies. Access to measured refractivity fields with high spatial and temporal resolution near the surface opens a new paradigm for understanding the convective processes within the boundary layer. It has been shown via advanced physical models that surface refractivity plays an important role in con vective processes and, therefore, is expected to be valuable for forecasting of the initiation and intensity of convective precipitation. For this project, the refractivity field is retrieved remotely using S-band radars by measuring the returned phase from ground clutter. Pioneering work of Fabry et. al. [J. Atmos. Oceanic Technol., 14, 978-987, 1997] has demonstrated the usefulness of this technique. By adopting this refractivity retrieval concept, an independent real-time software platform has been developed. The software was written with a modular design for portability and will be tested during the spring 2007 storm season on two radars in Oklahoma. Both the National Weather Radar Testbed (Phased Array), maintained by the National Severe Storm Laboratory (NSSL), and the WSR-88D weather radar near Oklahoma City (KTLX), supported by the Radar Operations Center (ROC), will be used for this study. Using the raw Level-I time series data from the radars, the modular software platform will be used to process the data in real-time for refractivity fields, which will be sent to the Norman Weather Forecast Office (WFO) for evaluation. Working closely with the WFO forecasters, qualitative assessment procedures will be followed to evaluate the usefulness of the refractivity fields for operational forecasting.

Cohen, R. A., D. M. Schultz, 2005: Contraction rate and its relationship to frontogenesis, the Lyapunov exponent, fluid trapping, and airstream boundaries. Monthly Weather Review, 133, 1353-1369.

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, R. A., D. M. Schultz, 2006: Reply. Monthly Weather Review, 134, 2644-2644.

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.

Conway, J. B., D. Nealson, J. J. Stagliano, A. V. Ryzhkov, D. S. Zrnic, 2005: A New C-band Polarimetric Radar with Simultaneous Transmission for Hydrometeor Classification and Rainfall Measurements. Extended Abstracts, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, AMS, CD-ROM, P12R.14.

Corfidi, S. F., S. J. Corfidi, D. M. Schultz, 2006: Toward a better understanding of elevated convection. Preprints, 23rd Conf. on Severe Local Storms, St. Louis, MO, USA, Amer. Meteor. Soc., CD-ROM, P1.5.

Available online at ://http://ams.confex.com/ams/23SLS/techprogram/paper_115485.htm.

Dabberdt, W. F., T. W. Schlatter, F. H. Carr, E. W. Friday, D. P. Jorgensen, S. Koch, M. Pirone, F. M. Ralph, J. Sun, P. Welsh, X. Zou, 2005: Multi-Functional Mesoscale Observing Networks. Bulletin of the American Meteorological Society, 86, 961-982.

The U.S. Weather Research Program (USWRP) sponsored a community workshop on the design and development of multifunctional mesoscale observing networks in support of integrated forecasting systems, on 8–10 December 2003 at the National Center for Atmospheric Research in Boulder, Colorado. The workshop goals were to identify challenges, needs, and opportunities involved in developing improved, economically viable, integrated atmospheric mesoscale observing, modeling, and information-delivery systems. Recommendations were sought for improved mesoscale observing networks that recognize the needs of users, modelers, and forecasters.

Doswell, C. A., D. M. Schultz, 2006: On the use of indices and parameters in forecasting severe storms. Electronic Journal of Severe Storms Meteorology, 1(3), 1-22.

This paper discusses our concept of the proper (and improper) use of diagnostic variables in severe-storm forecasting. A framework for classification of diagnostic variables is developed, indicating the limi-tations of such variables and their suitability for operational diagnosis and forecasting. The utility of diag-nostic indices and parameters as prognostic tools for forecasting is discussed, revealing the relevant issues in designing new diagnostic variables used for making weather forecasts. Finally, criteria required to claim that a new diagnostic variable represents an effective prognostic variable are proposed. We argue that few, if any, diagnostic variables have met these criteria for demonstrated utility at prognosis.

Available online at ://http://www.ejssm.org/ojs/index.php/ejssm/issue/view/3.

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.

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.

Elmore, K. L., M. E. Baldwin, D. M. Schultz, 2006: Field Significance Revisited: Spatial Bias Errors in Forecasts as Applied to the Eta Model. Monthly Weather Review, 134, 519-531.

The spatial structure of bias errors in numerical model output is valuable to both model developers and operational forecasters, especially if the field containing the structure itself has statistical significance in the face of naturally occurring spatial correlation. A semi-parametric
Monte Carlo method, along with a moving blocks bootstrap method is used to determine the field significance of spatial bias errors within spatially correlated error fields. This process can be completely automated, making it an attractive addition to the verification tools already in use. The process demonstrated here results in statistically significant spatial bias error fields at any arbitrary
significance level.

To demonstrate the technique, 0000 and 1200 UTC runs of the operational Eta model and the operational Eta model using the Kain–Fritsch convective parameterization scheme are examined. The resulting fields for forecast errors for geopotential heights and winds at 850, 700, 500, and 250 hPa over a period of 14 months (26 January 2001 through 31 March 2002) are examined and compared using the verifying initial analysis. Specific examples are shown, and some plausible causes for the resulting significant bias errors are proposed.

Elmore, K. L., D. M. Schultz, M. E. Baldwin, 2006: The Behavior of Synoptic-Scale Errors in the Eta Model. Monthly Weather Review, 134, 3355-3366.

A previous study of the mean spatial bias errors associated with operational forecast models motivated an examination of the mechanisms responsible for these biases. One hypothesis for the cause of these errors is that mobile synoptic-scale phenomena are partially responsible. This paper explores this hypothesis using 24-h forecasts from the operational Eta model and an experimental version called the EtaKF.
For a sample of 44 well-defined upper-level short-wave troughs arriving on the west coast of the United States, 70% were underforecast (as measured by the 500-hPa geopotential height), a likely result of being undersampled by the observational network. For a different sample of 45 troughs that could be tracked easily across the country, consecutive model runs showed that the height errors associated with 44% of the troughs generally decreased in time, 11% increased in time, 18% had relatively steady errors, 2% were uninitialized entering the west coast, and 24% exhibited some other kind of behavior. Thus, landfalling short-wave troughs were typically underforecast (positive errors, heights too high), but these errors tended to decrease as they moved across the United States, likely a result of being better initialized as the troughs became influenced by more upper-air data. Nevertheless, some errors in short-wave troughs were not corrected as they fell under the influence of supposedly increased data amount and quality. These results indirectly show the effect that the amount and quality of observational data has on the synoptic-scale errors in the models. On the other hand, long-wave ridges tended to be underforecast (negative errors, heights too low) over a much larger horizontal extent.
These results are confirmed in a more systematic manner over the entire dataset by segregating the model output at each grid point by the sign of the 500-hPa relative vorticity. Although errors at grid points with positive relative vorticity are small but positive in the western United States, the errors become large and negative farther east. Errors at grid points with negative relative vorticity, on the other hand, are generally negative across the United States. A large negative bias observed in the Eta and EtaKF over the southeast United States is believed to be due to an error in the longwave radiation scheme interacting with water vapor and clouds. This study shows that model errors may be related to the synoptic-scale flow, and even large scale features such as long-wave troughs can be associated with significant large-scale height errors.

Available online at ://http://ams.allenpress.com/.

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.

Fierro, A. O., L. Leslie, E. R. Mansell, G. J. Holland, J. M. Straka, 2006: Numerical simulations of the evolution of tropical cyclone electrification, lightning, microphysics, and dynamics at landfall: preliminary results. Preprints, Second Conference on Meteorological Applications of Lightning Data, Atlanta, GA, USA, American Meteorological Society, CD-ROM, P1.12.

Providing accurate and timely forecasts of the intensity and location of landfalling tropical cyclones (TCs) is a major meteorological challenge, and is increasingly important as coastal regions affected become more populated. A major unsolved problem is why TCs vary so much in their electrical activity. Some storms have little lightning activity, while others are extremely active, especially in their spiral cloud bands or within their eyewall as they intensify or weaken. At present, little is known about the evolution of charge and subsequent electrification in hurricanes, so our early results are a guideline for future studies. The findings are expected to have major implications for TC predictions and lightning observation strategies at landfall. We suggest that they may also lead to improved understanding of TC structure in general.

Toward this goal, a sophisticated cloud model featuring a 10-ICE microphysics scheme and a 3D branched lightning module explores the utility of a systematic monitoring of lightning activity such as flash rate, cloud to ground polarity and stroke multiplicity within TCs, as they strengthen or weaken over the ocean, especially when they make landfall. Of interest is how the microphysical and subsequent charge structure differs from, or resembles, that of electrically active continental convective systems such as supercells or mesoscale convective systems. A preliminary set of high-resolution numerical simulations were performed on a fine grid having a horizontal grid spacing of 3km and a vertical mean spacing of 600 m (45 height levels). The environmental initial conditions were from a composite sounding from TC Charley (2004), which showed a clear increase in lightning activity before intensifying from a borderline Category 3 to a high-end Category 4 storm on the Saffir-Simpson scale 8 hours before landfall on the west Florida coast. A meridionally orientated horizontal slab moving towards the TC at a fixed constant speed (of 8 m/s) was used as an initial simulation of landfall. More sophisticated landfall representations are being developed.

Preliminary results show that the highest total lightning flash rate are found within the stronger cells forming the outer rainbands and within the eyewall, where updraft speeds seldom exceed 15 m/s, consistent with observations. Significant charging capable to produce lightning flashes are collocated with regions having moderate graupel mixing ratio (> 0.5 g/kg) and moderate LWC (> 1 g/kg), namely within the eyewall and the strongest outer band cells. Using the Gardiner non-inductive scheme and weak inductive charging settings, the eyewall exhibits a normal tripole charge structure while a normal dipole is observed in the outer eyewall startiform region as induction responsible for the formation/enhancement of the lowest charge region becomes negligible there. The charges forming the dipole in the outer eyewall are generated within the eyewall via non-inductive collisional charging between graupel pellets and lighter ice crystals in the mixed-phase region at midlevels (~-15C isotherm level at 7km AGL) and are ejected radially outward by the centripetal force induced by the storm intense circulation at and near its center.

Available online at ://http://ams.confex.com/ams/Annual2006/techprogram/paper_103235.htm.

Fierro, A. O., M. S. Gilmore, L. J. Wicker, E. R. Mansell, J. M. Straka, 2006: Electrification and lightning in an idealized boundary-crossing supercell simulation of 2 June 1995. Monthly Weather Review, 134, 3171.

A nonhydrostatic cloud model with electrification and lightning processes was utilized to investigate how simulated supercell thunderstorms respond when they move into environments favorable for storm intensification. One model simulation was initialized with an idealized horizontally varying environment, characteristic of that observed across an outflow boundary in the west Texas Panhandle on 2 June 1995 with larger convective available potential energy (CAPE) and wind shear on the boundary’s cool side. That simulation was compared with a control simulation initialized without the boundary. The simulated right-moving supercell rapidly increased in updraft strength and volume, low-level rotation, radar reflectivity, and 40-dBZ echo-top height as it crossed the boundary, whereas the supercell that did not cross the boundary failed to intensify. For the same kinematic and microphysical evolution and the same inductive charging parameterization, four noninductive (NI) charging parameterizations were tested. In all four cases, there was a general tendency for the charge regions to be lofted higher within the updraft after crossing the boundary. Once the precipitation regions between the main storm and a secondary storm started merging farther on the cool side of the boundary, a gradual deepening and strengthening of the lowest charge regions occurred with relatively large increases in hail and graupel volume, charging rates, charge volume, charge density, and intracloud and cloud-to-ground (CG) flash rates. The negative charge present on graupel within the downdraft appeared to have a common origin via strong NI charging within the midlevel updraft in all four NI cases. Positive channels were more consistent in coming closer to the ground with time compared to negative channels within this graupel and hail-filled downdraft (four of four cases). Those NI schemes that also set up a positive dipole (three of four cases) or inverted tripole (two of four cases) above the downdraft had downward-propagating positive channels that reached ground as positive CG (+CG) flashes. The best overall performance relative to the 2 June 1995 CG lightning observations occurred within one of the rime-accretion-rate-based schemes and the Gardiner scheme as parameterized by Ziegler.

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.

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.

Gallus, W. A., M. E. Baldwin, K. L. Elmore, 2007: Evaluation of probabilistic precipitation forecasts determined from Eta and AVN forecasted amounts.. Weather and Forecasting, 22, 207-215.

This note examines the connection between the probability of precipitation and forecasted amounts from the NCEP Eta (now known as the North American Mesoscale model) and Aviation (AVN; now known as the Global Forecast System) models run over a 2-yr period on a contiguous U.S. domain. Specifically, the quantitative precipitation forecast (QPF)–probability relationship found recently by Gallus and Segal in 10-km grid spacing model runs for 20 warm season mesoscale convective systems is tested over this much larger temporal and spatial dataset. A 1-yr period was used to investigate the QPF–probability relationship, and the predictive capability of this relationship was then tested on an independent 1-yr sample of data. The same relationship of a substantial increase in the likelihood of observed rainfall exceeding a specified threshold in areas where model runs forecasted higher rainfall amounts is found to hold over all seasons. Rainfall is less likely to occur in those areas where the models indicate none than it is elsewhere in the domain; it is more likely to occur in those regions where rainfall is predicted, especially where the predicted rainfall amounts are largest. The probability of rainfall forecasts based on this relationship are found to possess skill as measured by relative operating characteristic curves, reliability diagrams, and Brier skill scores. Skillful forecasts from the technique exist throughout the 48-h periods for which Eta and AVN output were available. The results suggest that this forecasting tool might assist forecasters throughout the year in a wide variety of weather events and not only in areas of difficult-to-forecast convective systems.

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.

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.

Gochis, D., D. M. Schultz, . et al., 2005: The Water Cycle Across Scales. Bulletin of the American Meteorological Society, 86, 1743-1746.

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/.

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.

Hane, C. E., D. L. Andra Jr., K. Trammell, F. H. Carr, 2005: Development of a tool to aid in forecasting the evolution of Great Plains MCSs during late morning hours. AIRMASS 2005 Conference, Wichita, KS, USA, American Meteorological Society, CD-ROM, XXXX.

Hane, C. E., D. L. Andra, Jr., J. A. Haynes, T. E. Thompson, F. H. Carr, 2005: On the Importance of Environmental Factors in Influencing the Evolution of Morning Great Plains MCS Activity during the Warm Season. Extended Abstracts, Eleventh Conference on Mesoscale Processes, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, P3M.6.

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. L., D. M. Schultz, 2006: Intraseasonal variability of summertime storms over central Arizona during 1997 and 1999. Weather and Forecasting, 21, 559-578.

Although previous climatologies over central Arizona show a summer diurnal precipitation cycle, on any given day precipitation may differ dramatically from this climatology. The purpose of this study is to investigate the intraseasonal variability of diurnal storm development over Arizona and explore the relationship to the synoptic-scale flow and Phoenix soundings during the 1997 and 1999 North American Monsoons (NAMs). Radar reflectivity mosaics constructed from Phoenix and Flagstaff Weather Surveillance Radar-1988 Doppler (WSR-88D) reflectivity data reveal six repeated storm development patterns or regimes. The diurnal evolution of each regime is illustrated by computing frequency maps of reflectivity 25 dBZ and greater during 3-h periods. These regimes are named to reflect their regional and temporal characteristics: dry regime (DR), Eastern Mountain regime (EMR), Central–Eastern Mountain regime (CEMR), Central–Eastern Mountain and Sonoran-isolated regime (CEMSIR), Central–Eastern Mountain and Sonoran regime (CEMSR), and nondiurnal regime (NDR).
Composites constructed from the National Center for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) Reanalysis Project data show that regime occurrence is related to the north–south location of the 500-hPa geopotential height ridge axis of the Bermuda High and the east–west location of the 500-hPa monsoon boundary, a boundary between dry air to the west and moist air to the east. Consequently, precipitable water (PW) from 1200 UTC Phoenix soundings is the best parameter for discriminating the six regimes.

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.

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.

Horgan, K. L., D. M. Schultz, R. H. Johns, S. F. Corfidi, J. E. Hales, 2006: A five-year climatology of elevated severe convective storms in the United States east of the Rocky Mountains. Preprints, Severe Local Storms Special Symposium, Atlanta, GA, USA, Amer. Meteor. Soc., CD-ROM, P1.22.

Available online at ://http://www.cimms.ou.edu/~schultz/papers/horganetal2006.pdf.

Horgan, K. L., D. M. Schultz, R. H. Johns, J. E. Hales, S. F. Corfidi, 2007: A five-year climatology of elevated severe convective storms in the United States east of the Rocky Mountains. Weather and Forecasting, 22, 1031-1044.

James, M. R., R. D. Palmer, T.-Y. Yu, S. M. Torres, R. J. Doviak, D. S. Zrnic, 2005: Implementation of refractivity retrieval from ground clutter using the S-band KOUN radar. Preprints, 32nd International Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, 4R.7.

Johnson, E. V., E. R. Mansell, 2006: Three dimensional lightning mapping of the central Oklahoma supercell on 26 May 2004. Extended Abstracts, Second Conference on Meteorological Applications of Lightning Data, Atlanta, GA, USA, American Meteorological Society, CD-ROM, 6.5.

Three-dimensional lightning mapping observations from the Oklahoma Lightning Mapping Array (OK-LMA) were used to analyze charge structure of a splitting supercell on 26 May 2004 during the Thunderstorm Electrification and Lightning Experiment (TELEX). The OK-LMA was used to evaluate cloud-to-ground (CG) flashes reported by the National Lightning Detection Network's (NLDN). Each NLDN flash between 2300 UTC and 2310 UTC was classified as either a CG or an intra-cloud (IC) flash using LMA-inferred charge structure. The LMA analysis of the charge structure supports charge structure for 23% of the positive CGs. Most of the negative NLDN flashes that were analyzed were not confirmed by the LMA.

Available online at ://http://ams.confex.com/ams/Annual2006/techprogram/paper_104352.htm.

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.

Kanak, K. M., J. M. Straka, D. M. Schultz, 2006: Simulations of mammatus-like clouds and comparison with observations, cloud based detrainment instability theory and Scorer's conjectures.. Preprints, 12th Conf. Cloud Physics, Madison, WI, USA, Amer. Meteor. Soc., CD-ROM, P1.57.

Available online at ://http://ams.confex.com/ams/Madison2006/techprogram/paper_112359.htm.

Killeen, T. J., M. Douglas, T. Consiglio, P. M. Jorgensen, J. Mejia, 2007: Dry spots and wet spots in the Andean hotspot. Journal of Biogeography, 34, .

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.

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.

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, D. Rust, P. Krehbiel, B. Rison, 2007: Lightning in the anvil region of a supercell storm. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, IUGG/Commission on Atmospheric Electricity, PS5-8.

The Thunderstorm Electrification and Lightning Experiment (TELEX) took place in central Oklahoma during the 2003 and 2004 convective seasons to study the lightning, dynamics and microphysics of thunderstorms. One storm from this field project, a high-precipitation tornadic supercell occurred on 29 May 2004. In this storm, the Oklahoma Lightning Mapping Array detected lightning extending over one hundred kilometers away from the core of the supercell. Lightning is known to occur in the anvil region of supercells; typically this lightning is initiated in the core of the storm and extends out through the anvil. In the 29 May 2004 storm, however, some flashes actually initiated in the anvil region and the subsequent leaders progressed back towards the core of the storm. Some of these flashes were negative cloud-to-ground flashes that initiated over 50 km away from the core and struck ground beneath the anvil close to the initiation point. It appears that interaction between the anvil of this supercell and an anvil of opposite polarity from a weaker left-moving cell to the north was responsible for initiating this lightning.

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.

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

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

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

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

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.

Lund, N., D. MacGorman, D. Rust, T. Schuur, P. Krehbiel, W. Rison, T. Hamlin, J. Straka, M. Biggerstaff, 2007: Relationship between lightning location and polarimetric radar signatures in an MCS. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, IUGG/Commission on Atmospheric Electricity, PS5-2.

The relationship of lightning initiation and structure to the storm microphysics and structure depicted by polarimetric radar has been analyzed for a small mesoscale convective system (MCS) that occurred on 19 June 2004 during the Thunderstorm Electrification and Lightning Experiment (TELEX). Horizontal reflectivity (Z), differential reflectivity (Zdr), specific differential phase (Kdp) and correlation coefficient (ρHV) data were gathered by a 10-cm, polarimetric radar located in Norman, Oklahoma. Three-dimensional lightning structure was mapped by the Oklahoma Lightning Mapping Array (OK-LMA), and ground strike points were mapped by the United States National Lightning Detection Network. OK-LMA data were processed to group mapped points into flashes and to determine the initiation location of each flash that contained more than 10 mapped points. The initiation location was calculated by sequentially eliminating outliers among the first 10 points that occurred in a flash, with no fewer than 5 points being used in the final initiation location. The initiation location and mapped points for each flash were superimposed on polarimetric radar data in order to investigate lightning relationships with storm structure. The lightning initiation points tended to cluster together in one of two altitude ranges and were almost all in the convective line. Initial results show a relationship between the lightning initiation locations and radar signatures in both Z and Kdp. In the lower altitude range, between 3 and 5 km MSL, initiation locations tended to cluster around updraft cores, in regions characterized by a transition in Z from 50 to 55 dBZ and a transition in Kdp from 0.4 to 0.5 deg/km. In the upper range, between 8 and 10 km MSL, initiation points tended to cluster directly above the updrafts, in regions characterized by a transition in Z from 42.5 to 47.5 dBZ and in Kdp from 0.075 to 0.150 deg/km. The two-layer nature of the initiation points is consistent with grossly tripolar structure of the charge distribution involved in lightning in the convective line. Also, the horizontal pattern of the initiation locations has a quasi-periodic horizontal structure which is 180 degrees out of phase with the maximum updraft locations for the lower region and is in phase with the maximum updraft locations for the upper region. There were also a few flash initiations within the stratiform region, possibly associated with decaying cells. The values of Z and Kdp associated with these initiation points were smaller than in the convective line, but as in the convective line, the initiations also occurred along gradients, above a local maximum, in these parameters.

Lund, N., D. R. MacGorman, W. D. Rust, T. J. Schuur, P. Krehbiel, W. Rison, T. Hamlin, J. Straka, M. Biggerstaff, 2008: Relationship between lightning location and polarimetric radar signatures in an MCS. Preprints, 3rd Conference on Meteorological Applications of Lightning Data, New Orleans, LA, USA, American Meteorological Society, P1.5.

MacGorman, D. R., W. D. Rust, P. Krehbiel, W. Rison, E. Bruning, K. Wiens, 2005: The electrical structure of two supercell storms during STEPS. Monthly Weather Review, 133, 2583-2607.

Balloon soundings were made through two supercell storms during the Severe Thunderstorm Electrification and Precipitation Study (STEPS) in summer 2000. Instruments measured the vector electric field, temperature, pressure, relative humidity, and balloon location. For the first time, soundings penetrated both the strong updraft and the rainy downdraft region of the same supercell storm. In both storms, the strong updraft had fewer vertically separated charge regions than found near the rainy downdraft, and the updraft's lowest charge was elevated higher, its bottom being near the 40-dBZ boundary of the weak-echo vault. The simpler, elevated charge structure is consistent with the noninductive graupel-ice mechanism dominating charge generation in updrafts. In the weak-echo vault, the amount of frozen precipitation and the time for particle interactions are too small for significant charging. Inductive charging mechanisms and lightning may contribute to the additional charge regions found at lower altitudes outside the updraft. Lightning mapping showed that the in-cloud channels of a positive ground flash could be in any one of the three vertically separated positive charge regions found outside the updraft, but were in the middle region, at 6-8 km MSL, for most positive ground flashes. Our data are consistent with the electrical structure of these storms having been inverted in polarity from that of most storms elsewhere. We hypothesize that the observed inverted-polarity cloud flashes and positive ground flashes were caused by inverted-polarity storm structure, possibly due to a larger than usual rime accretion rate for graupel in a strong updraft.

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., K. Kuhlman, D. Rust, M. Biggerstaff, T. Schuur, J. Straka, P. Krehbiel, B. Rison, L. Carey, 2007: Lightning and electrical structure of a heavy-precipitation supercell storm during TELEX. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, IUGG/Commission on Atmospheric Electricity, OS5-1.

The Thunderstorm Electrification and Lightning Experiment (TELEX) observed a heavy-precipitation (HP) supercell storm in central Oklahoma on 29 May 2004. In a HP supercell storm, the initial location of the mesocyclone, which is the parent rotation of tornadoes, is embedded well within the precipitation of the storm, instead of being on the edge of the storm (as in classic and low-precipitation supercell storms). Two 5-cm wavelength mobile Doppler radars were positioned near the storm and collected volume scans every 3 minutes for 3 h beginning as the storm became supercellular. The storm had supercell characteristics for this entire period. The Oklahoma Lightning Mapping Array provided three-dimensional data throughout the storm’s supercellular stage and provided two-dimensional data from the time of storm initiation in western Oklahoma. A 10-cm wavelength polarimetric radar also provided data for much of this period.
Lightning flash rates became extraordinarily large as the storm evolved into a supercell and its motion turned rightward. Flash rates increased again (to an estimated peak value of almost 500 flashes per minute) shortly before the storm produced a tornado rated F2 on the Fujita scale. During this period, an upward pulse in lightning density extended as high as 18 km MSL in a plume extending above the equilibrium level, and the region of lightning activity pulsed eastward far into the anvil, up to 150 km from the western edge of the storm. A series of minimums in the plan projection of lightning density (i.e., lightning holes) formed just above the bounded weak echo region. A dual-Doppler synthesis of wind during one volume scan shows the lightning hole was co-located with large vertical wind speeds in the rotating updraft. The hole apparently occurred because precipitation particles had little time to grow and gain charge in the strong updraft before they were lifted to upper regions of the storm and advected outward by flow from the diverging updraft. Cloud-to-ground lightning activity in and near heavy precipitation was dominated initially by negative ground flashes, but during part of the supercell phase, evolved to become dominated by positive ground flashes. Lightning mapping data suggest that, when positive ground flashes dominated, the vertical polarity of the storm’s electrical structure was inverted from the usual polarity.

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.

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.

Marchand, R. N., N. Beagley, S. Thompson, T. P. Ackerman, D. M. Schultz, 2006: A bootstrap technique for testing the relationship between local-scale radar observations of cloud occurrence and large-scale atmospheric fields. Journal of the Atmospheric Sciences, 63, 2813-2830.