Abstract
Abstract
Derechos are widespread, destructive windstorms produced by mesoscale convective systems (MCSs). Past studies have shown various layers of vertical wind shear, and possibly thermodynamic variables like lapse rates and instability, to be of use in forecasting MCS wind swath intensity, up to and including derechos. A recent proposal to enhance the wind criteria for derechos, as well as the availability of a long-term MCS dataset, motivated a new analysis of derecho and non-derecho MCS environments. Midlevel lapse rates, bulk shear in the 0–6-km above ground layer or deeper, mean wind speed in the uppermost 3 km below the tropopause, and combined parameters that incorporate lapse rates and deep shear discriminate best between derechos and non-derechos in early life and around the onset of peak intensity. Regional variations also appear: deep-layer shear is the best discriminator in the Central and Southern Plains, while midlevel lapse rates discriminate somewhat better than shear in the Midwest and Ohio Valley. Weakly forced, lower-predictability derechos, which are the focus of this study, also tend to have weaker shear at low levels and midlevels, slower mean winds, and lower storm-relative helicity than derechos associated with synoptic troughs upstream.