MODELS and ASSIMILATION

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

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

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

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

NSSL Outstanding Scientific Paper Award

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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.

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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. 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.

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

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

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

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

NOAA Outstanding Publication Award in 2006

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

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

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Pinto, J., C. Kessinger, B. Hendrickson, D. Megenhardt, P. Harasti, Q. Xu, P. Zhang, Q. Zhao, M. Frost, J. Cook, S. Potts, 2007: Storm characterization and short term forecasting potential using a phase array radar. Extended Abstracts, 33rd Conference on Radar Meteorology. 6–10 August 2007, Cairns, Australia. Amer. Meteor. Soc.,, Cairns, Australia, Amer. Meteor. Soc., P5.18.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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