The High Shear/Low CAPE Problem: Improving Detection of Significant Weather Events in Marginally Unstable Environments

Environments consisting of large 0-6 km shear (≥ 35 knots) and low surface-based convective available potential energy (CAPE; ≤ 500 J kg^-1) have been associated with a substantial fraction of severe weather events across the mid-Atlantic and southeastern United States over the last decade, including dozens of significant (EF2 or greater on the Enhanced Fujita scale) tornadoes. High shear/low CAPE (HSLC) events remain a challenge for operational meteorologists at local National Weather Service (NWS) Weather Forecast Offices (WFOs) and the NWS Storm Prediction Center (SPC) due to their tendency to occur during climatologically unfavorable times and environments. Research on HSLC events has been limited to few studies over the past two decades, and overall understanding of HSLC environments is poor.

The purpose of this study is to identify discriminating environmental features between significant HSLC events and non-severe HSLC convection. Primarily, through statistical analysis and case studies, we will explore the utility of environmental parameters and existing composite parameters in diagnosing areas favorable for significant tornadoes, significant winds (≥ 65 knots), and significant hail (≥ 2” in diameter) while reducing false alarms. The results will lead into a discussion on the practicality of developing a composite parameter suited for HSLC environments.