Synoptic Influence on High Shear, Low CAPE Convective Events

High shear, low CAPE (HSLC) severe weather events present a challenge for forecasters, commonly occurring during the cold season and overnight hours. In order to further improve forecasting and nowcasting of HSLC severe weather events, it is important that forecasters know and understand the characteristics of these convective environments, including how convection is initiated and sustained. The goal of this research is to understand the progression of HSLC environments prior to and during convection, and to determine the degree to which the synoptic environment influences convective ingredients in these cases. Our approach is to perform both case study and idealized simulations of two observed HSLC events.

The first HSLC case is a severe quasi-linear convective system (QLCS) that occurred during overnight hours on January 29-30, 2013 in Tennessee and southern Kentucky. The second HSLC case exhibited scattered convection containing several severe mini-supercells on February 10, 2013 in Mississippi. The QLCS was well simulated with the WRF-ARW using reanalysis data. It is evident that the pre-convective environment was destabilized and moistened over time, possibly by synoptic scale lifting. A HSLC profile from this pre-convective environment was then initialized in an idealized simulation using CM1. These profiles were rather dry aloft, and exhibited potential instability. In the idealized runs, convection only developed when a significant wedge-shaped cold slab was used, implying that the environment would not support convection without additional broad lifting (and the possible release of the potential instability). Further analysis, and work pertaining to the mini-supercell outbreak, is ongoing and will be detailed at the conference.