S31 Characteristics and estimated warning success rates of QLCS and supercell-produced significant tornadoes in the Southeast U.S

Sunday, 23 January 2011
Garrett D. Combs, Lyndon State College, Lyndonville, VT; and S. Nelson

The primary objective of this poster was to compare storm characteristics, derived from National Weather Service (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 National Climatic Data Center (NCDC) from November 2007 to May 2010. Mesocyclone rotational velocity and diameter were computed by manually interrogating Level II radar data over an approximately 30 minute period prior to and immediately following each event. Based on this analysis, each type of tornado associated with each storm was classified as supercell or QLCS. Of the tornado events examined during this time period, 71% were produced by supercells and 29% by QLCS. Supercell tornadoes had approximately 1 to 3 ms-1 greater rotational velocity values on average than QLCS cases. However, the trends in the rotational velocity were nearly equivalent between the two storm types. Diameter trends were approximately similar as well. NWS Weather Forecast Office (WFO) storm-based warning information was also downloaded and analyzed. WFO warnings during QLCS cases were found to have significantly shorter lead time and lower accuracy than with supercells. The average initial lead time for QLCS events was nearly 7 minutes lower (19 min vs. 12 min) and the accuracy, as measured by the percentage of event warned (PEW) metric, was 18% lower (95% vs. 77%).
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