Tornado failure modes in central and southern Great Plains severe thunderstorm episodes

Several ingredients are important to the formation of supercell thunderstorms capable of producing significant tornadoes: sufficient moisture, instability, vertical wind shear, and a convective mode dominated by discrete storms. If any of these ingredients are substantially limited, then the threat for significant tornadoes decreases correspondingly. This work will explore the relative frequency of “missing” ingredients for significant tornadoes in severe storm days across the Great Plains.

Spring severe thunderstorm episodes will be examined across the central and southern Great Plains (Nebraska to Texas). Specifically, we will examine all severe weather events with > 50 severe storm reports from Nebraska to central Texas during the period 2000-2006. Important tornado days will be identified, such as days containing multiple tornadoes with relatively long tracks or wide damage paths, or F2-F5 tornado damage. Representative values of 100 mb mean parcel CAPE, 0-6 km bulk vector shear, 0-1 km storm-relative helicity, and surface temperature-dew point temperature spread will be derived from archived soundings and surface observations for each case. The observed values in each case will be compared to “threshold” values based on the supercell proximity sounding sample presented by Thompson et al. (2006), with emphasis on identifying those days where one or more significant supercell tornado ingredients were sub-optimal. Primary convective mode (linear or discrete cells) will be established via regional radar reflectivity mosaics.