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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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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.

Publications Copernicus
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)...