The Temporal Evolution of Severe vs. Non-Severe High Shear Low CAPE Environments

Abstract:

High-shear low-CAPE (HSLC) severe weather events, defined as those in which surface-based CAPE is below 500 J/kg or most unstable CAPE is less than 1000 J/kg and have a 0-6 km bulk wind difference of at least 18 m/s, are uniquely challenging to forecasters due to their rapid evolution times and relatively infrequent production of severe weather. Additionally, these environments tend to occur during the cool season and overnight hours, which present their own challenges in terms of current conceptual understanding and forecaster verification. To better understand how rapid environmental evolution contributes to severe weather production in HSLC environments, nearly 250 tornado reports from HSLC events in the southeastern U.S. between 2014-2018 were categorized based on their radar signature near the time of tornadogenesis. More than half of the reports were from supercells, with the next largest contributor being bowing segments. Next, model soundings are used to characterize the near-storm environment and its temporal evolution, focusing on the time of tornadogenesis, as well as the hour before. For comparison, two nearby locations not associated with tornadoes also had their environmental evolution quantified. Differences in environmental shifts between tornadic and non-tornadic reports will be shown, along with sensitivities to associated radar signatures, time of day, and time of year. The goal of this study is to enhance short-term forecasts of HSLC events by quantifying the impact and degree of environmental variability associated with severe and non-severe convection.