Using short-range ensemble forecasts for predicting severe weather events

An ensemble of mesoscale model simulations of the most severe tornadic outbreak of the modern period, 24-25 June 1967, is examined. Results indicate that the fields of convective available potential energy (CAPE), storm-relative environmental helicity (SREH), and bulk Richardson number shear (BRNSHR), are able to provide useful guidance on the region of tornadic supercell thunderstorms for this outbreak. CAPE is used to define the region in which convection is possible, SREH is used to define the region in which thunderstorms are likely to be supercells, and BRNSHR is used to define the region in which low-level mesocyclogenesis is more likely. These results highlight the potential value of analyzing various severe weather parameters in forecasting tornadic thunderstorms, and the value of mesoscale ensemble forecasts for predicting severe, life threatening weather events in Europe. The ensemble also clearly shows the sensitivity and uncertainty of the model simulations to the physical process schemes used. Variations in all three severe weather parameters are significant near regions of convection, which unfortunately are where forecasters need these parameter values to be most reliable. These sensitivities highlight the value of an ensemble system for short-range weather forecasting, since it is clear that if a single model forecast of convective activity goes awry, then it provides little guidance to forecasters concerned with threats to life and property from severe weather. Published by Elsevier Science B.V.