The Origins of Rotation within High-Shear, Low-CAPE Mesovortices and Mesocyclones

A large fraction of eastern U.S. cool season and overnight tornadoes and significant straight-line wind events occur within high-shear, low-CAPE (HSLC) environments; however, this portion of the parameter space is also associated with low probability of detection and high false alarm rates of NWS watch and warning products. The compact spatial dimensions of HSLC mesovortices and mesocyclones (~2-4 km in diameter and depth) make their interrogation by radar challenging. Additionally, these sizes are comparable to the grid spacing of operational convection-allowing models, meaning that they are poorly (if at all) represented in high-resolution numerical weather prediction.

The purpose of this work is to evaluate high-resolution, idealized simulations of HSLC QLCSs in an attempt to elucidate the origins of rotation within these embedded mesovortices and mesocyclones. Data collected near HSLC convection during recent field projects, along with observed and modeled soundings from case studies and climatologies of severe HSLC convection, are used as a basis for the homogeneous, idealized environment in these simulations. In addition to process studies focused on the origins of rotation, sensitivity studies varying the vertical distributions of CAPE and shear are undertaken to determine what environmental characteristics promote versus curb the development of embedded supercells and mesovortices.