The threat of severe weather across the Mid-Atlantic and Southeast has been well advertised with the initial threat noted in the “Day 5” portion of the SPC 4-8 Day Severe Weather Outlook issued on 17 February. Today’s potential for severe weather is focused on damaging wind gusts while brief QLCS events could result in short episodes of an increased tornado threat.
For multiple days the SHERB parameter has highlighted the potential for an enhanced severe weather threat associated with a High-Shear Low CAPE (HSLC) environment on the northern periphery of region of more favorable surface-based instability located across southeastern NC and SC. The SHERB parameter was developed as a part of an NC State-NWS CSTAR project. You can learn more about it in a PDF version of a presentation entitled Improving Forecasting of High Shear, Low CAPE Severe Weather Environments.
SHERB guidance from multiple runs of the NAM and other NWP sources have shown an enhanced HSLC threat across northeastern NC and southeastern NC this afternoon, centered around 18 UTC, with SHERB values greater than 1 (see the first image below). These locations are forecast to have an air mass characterized by SBCAPE values of around or possibly a little more than 500 J/Kg and MUCAPE values of close to 1000 J/Kg, meaning they are a borderline HSLC case (see 03Z SREF forecast for KRDU valid 18z in the second image below). Despite the more limited surface based instability in these regions than locations further south, the SHERB highlights this region as especially susceptible to severe weather which is consistent with the 12 UTC SPC Severe Weather Outlook.