The Impacts of Wind Shear on Derecho Development and Maintenance

Derechos pose a considerable threat to communities in their damage path, capable of overwhelming emergency responders and causing billions in property damage. Classified as a large and damaging windstorm generated by a Mesoscale Convective System, derechos must produce severe wind reports (26+ m/s or 58+ mph) in swaths at least 400 km (~250 miles) long, and at least 97 km (~60 miles) wide, with no more than 1 hour between reports. Progressive derechos, those primarily organized and driven by their own convective outflows rather than synoptic scale features, are difficult to forecast because they tend to be subtly forced. There remains uncertainty within the literature about the relative importance of low level and deep layer shear in relation to the intensity and longevity of these windstorms. Given the challenge progressive derechos present forecasters, we elected to sample robust progressive derechos with widespread significant severe wind in weakly forced synoptic regimes. By utilizing this sample set and a representative sample of less severe MCS wind events to compare with, we explore the overall hodograph shape, line-normal shear in the RKW framework (Weisman et al. 1988), deeper-layer shear, storm-relative inflow and helicity, and other MCS-relative kinematic parameters using the SPC's SfcOA/RUC archive to represent proximity environments. Understanding the relationship to its kinematic environment is pivotal to forecasting the most damaging of derechos, enabling forecasters to better protect communities within the large and destructive paths of these windstorms.