P4.20 Characteristics and Estimated Warning Success Rates of QLCS and Supercell-Produced Significant Tornadoes in the Southeast United States

Tuesday, 12 October 2010
Grand Mesa Ballroom ABC (Hyatt Regency Tech Center)
Steven E. Nelson, NOAA/NWS, Peachtree City, GA; and G. D. Combs

The primary objective of this study was to compare storm characteristics, derived from NWS Doppler radar data, and warning success measures for significant tornadoes (EF2 and greater) in the Southeastern U.S. originating from supercell thunderstorms and quasi-linear convective systems (QLCS). Non-tropical, significant tornado events were obtained from the National Climatic Data Center for November 2008 to April 2010. Mesocyclone rotational velocity and diameter were computed by manually interrogating the WSR-88D Level II data over an approximately 30 minute period prior to and immediately following each event. Based on this analysis, the type of storm with which each tornado was associated was classified as supercell or QLCS.

Of the 254 tornado events examined, around 10% were identified as significant. Of these, about 80% were produced by supercells and about 20% by QLCS. Supercell tornadoes had approximately 10 kt greater rotational velocity values, on average, than QLCS cases. However, the trends in the rotational velocity, as well as the average mesocyclone diameters, were nearly the same for both the two storm types.

NWS Weather Forecast Office (WFO) storm-based warnings were also analyzed. WFO warnings during QLCS cases were found to have significantly shorter lead times and lower accuracy than with supercells. The average initial lead time for QLCS events was nearly 14 minutes shorter (4 min vs 18 min) and the accuracy, as measured by the Percent of Events Warned metric, was about 20% lower (93% vs 72%).

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