The S2K Severe weather detection algorithms and their performance

One of the main goals of the Sydney 2000 Forecast Demonstration Project was to demonstrate the efficacy and utility of automated severe weather detection radar algorithms. As a contribution to this goal, this paper describes the radar-based severe weather algorithms used in the project, their performance, and related radar issues. Participants in this part of the project included the National Severe Storm Laboratory (NSSL) Warning Decision Support System (WDSS), the Meteorological Service of Canada Canadian Radar Decision Support (CARDS) system, the National Center for Atmospheric Research Thunderstorm Initiation, Tracking, Analysis, and Nowcasting (TITAN) system, and a precipitation-typing algorithm from the Bureau of Meteorology Research Centre polarized C-band polarimetric (C-Pol) radar. Three radars were available: the S-band reflectivity-only operational radar, the C-band Doppler Kurnell radar, and the C-band Doppler polarization C-Pol radar. The radar algorithms attempt to diagnose the presence of storm cells; provide storm tracks; identify mesocyclone circulations, downbursts and/or microbursts, and hail; and provide storm ranking. The tracking and identification of cells was undertaken using TITAN and WDSS. Three versions of TITAN were employed to track weak and strong cells. Results show TITAN cell detection thresholds influence the ability of the algorithm to clearly identify storm cells and also the ability to correctly track the storms. WDSS algorithms are set up with lower-volume thresholds and provided many more tracks. WDSS and CARDS circulation algorithms were adapted to the Southern Hemisphere. CARDS had lower detection thresholds and, hence, detected more circulations than WDSS. Radial-velocity-based and reflectivity-based downburst algorithms were available from CARDS. Since the reflectivity-based algorithm was based on features aloft, it provided an earlier indication of strong surface winds. Three different hail algorithms from WDSS, CARDS, and C-Pol provided output on the presence, the probability, and the size of hail. Although the algorithms differed considerably they provided similar results. Size distributions were similar to observations. The WDSS provided a ranking algorithm to identify the most severe storm. Many of the algorithms had been adapted and altered to account for differences in radar technology, configuration, and meteorological regime. The various combinations of different algorithms and different radars provided an unprecedented opportunity to study the impact of radar technology on the performance of the severe weather algorithms. The algorithms were able to operate on both single- and dual-pulse repetition frequency Doppler radars and on C- and S-band radars with minimal changes. The biggest influence on the algorithms was data quality. Beamwidth smoothing limited the effective range of the algorithms and ground clutter and ground clutter filtering affected the quality of the low-level radial velocities and the detection of low-level downbursts. Cycle time of the volume scans significantly affected the tracking results.

[1]  James W. Wilson,et al.  The 3 November Tornadic Event during Sydney 2000: Storm Evolution and the Role of Low-Level Boundaries , 2004 .

[2]  Harold E. Brooks,et al.  Verification of Nowcasts from the WWRP Sydney 2000 Forecast Demonstration Project , 2004 .

[3]  T. Keenan.  The World Weather Research Programme (WWRP) Sydney 2000 Forecast Demonstration Project: Overview , 2001 .

[4]  Stacy R. Stewart.  The prediction of pulse-type thunderstorm gusts using vertically integrated liquid water content (VIL) and the cloud top penetrative downdraft mechanism , 1991 .

[5]  Elizabeth E. Ebert,et al.  The Sydney 2000 Olympic Games Forecast Demonstration Project: Forecasting, Observing Network Infrastructure, and Data Processing Issues , 2004 .

[6]  A. Waldvogel,et al.  Criteria for the Detection of Hail Cells , 1979 .

[7]  Arthur Witt,et al.  The National Severe Storms Laboratory Tornado Detection Algorithm , 1998 .

[8]  R. Donaldson.  RADAR REFLECTIVITY PROFILES IN THUNDERSTORMS , 1961 .

[9]  Peter T. May,et al.  Radar Characteristics of Storms in the Sydney Area , 2000 .

[10]  M. Dixon,et al.  TITAN: Thunderstorm Identification, Tracking, Analysis, and Nowcasting—A Radar-based Methodology , 1993 .

[11]  Arthur Witt,et al.  The Storm Cell Identification and Tracking Algorithm: An Enhanced WSR-88D Algorithm , 1998 .

[12]  Elizabeth E. Ebert,et al.  Sydney 2000 Forecast Demonstration Project: Convective Storm Nowcasting , 2004 .

[13]  Donald W. Burgess,et al.  Automatic Detection of Mesocyclonic Shear with Doppler Radar , 1985 .

[14]  A. Witt,et al.  An Enhanced Hail Detection Algorithm for the WSR-88D , 1998 .

[15]  K. Emanuel.  A Similarity Theory for Unsaturated Downdrafts within Clouds , 1981 .

[16]  N. I Fox.  Assessing the impact of advanced nowcasting systems on severe weather warning dissemination , 2001 .

[17]  H. Brooks,et al.  Recent progress in the operational forecasting of summer severe weather , 1995 .

[18]  Neil I. Fox,et al.  The Impact of Advanced Nowcasting Systems on Severe Weather Warning during the Sydney 2000 Forecast Demonstration Project: 3 November 2000 , 2004 .

[19]  David M. L. Sills.  Meteorological aspects of the 3 November 2000 severe storms in Sydney, Australia , 2001 .

[20]  P. Joe,et al.  Correction of Dual PRF Velocity Errors for Operational Doppler Weather Radars , 2003 .

[21]  T. Bird,et al.  The BMRC/NCAR C-Band Polarimetric (C-POL) Radar System , 1998 .

[22]  Donald W. Burgess,et al.  The National Severe Storms Laboratory Mesocyclone Detection Algorithm for the WSR-88D* , 1998 .

[23]  Barbara G. Brown.  Forecast verification activities for the Sydney 2000 Forecast Demonstration Project , 2001 .

[24]  Elizabeth M. Quoetone,et al.  Warning Decision Making: The Relative Roles of Conceptual Models, Technology, Strategy, and Forecaster Expertise on 3 May 1999 , 2002 .

[25]  J. Bally,et al.  The Societal, Social, and Economic Impacts of the World Weather Research Programme Sydney 2000 Forecast Demonstration Project (WWRP S2000 FDP) , 2004 .