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Volume 18, issue 4 | Copyright
Nat. Hazards Earth Syst. Sci., 18, 1261-1277, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Apr 2018

Research article | 27 Apr 2018

Characterizing severe weather potential in synoptically weakly forced thunderstorm environments

Paul W. Miller and Thomas L. Mote Paul W. Miller and Thomas L. Mote
  • Department of Geography, University of Georgia, Athens, GA 30602, USA

Abstract. Weakly forced thunderstorms (WFTs), short-lived convection forming in synoptically quiescent regimes, are a contemporary forecasting challenge. The convective environments that support severe WFTs are often similar to those that yield only non-severe WFTs and, additionally, only a small proportion of individual WFTs will ultimately produce severe weather. The purpose of this study is to better characterize the relative severe weather potential in these settings as a function of the convective environment. Thirty-one near-storm convective parameters for > 200000 WFTs in the Southeastern United States are calculated from a high-resolution numerical forecasting model, the Rapid Refresh (RAP). For each parameter, the relative odds of WFT days with at least one severe weather event is assessed along a moving threshold. Parameters (and the values of them) that reliably separate severe-weather-supporting from non-severe WFT days are highlighted.

Only two convective parameters, vertical totals (VTs) and total totals (TTs), appreciably differentiate severe-wind-supporting and severe-hail-supporting days from non-severe WFT days. When VTs exceeded values between 24.6 and 25.1°C or TTs between 46.5 and 47.3°C, odds of severe-wind days were roughly 5 ×  greater. Meanwhile, odds of severe-hail days became roughly 10 ×  greater when VTs exceeded 24.4–26.0°C or TTs exceeded 46.3–49.2°C. The stronger performance of VT and TT is partly attributed to the more accurate representation of these parameters in the numerical model. Under-reporting of severe weather and model error are posited to exacerbate the forecasting challenge by obscuring the subtle convective environmental differences enhancing storm severity.

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Short summary
The likelihood of severe weather events in synoptically weakly forced thunderstorm (WFT) environments is best characterized by lapse-rate-based parameters. These measures, also among the most accurate model-derived variables, are posited to best capture the subtle convective environmental differences that favor WFT severity. Forecasters should consider weighting their WFT forecasts in favor of lapse-rate-based parameters over others that may be more sensitive to model biases.
The likelihood of severe weather events in synoptically weakly forced thunderstorm (WFT)...