Sensitivities of Simulated High-Shear, Low-CAPE Convection to Low-Level Bulk Wind Shear and Lapse Rates

High-shear, low-CAPE (HSLC) environments pose a challenge for operational forecasters, as evident by their associated low probability of detection of tornadoes and high false alarm rate of tornado warnings. Recent work has documented the skill of low-level shear vector magnitudes and low-level lapse rates in discriminating between severe and nonsevere HSLC convective events; however, the dynamics behind this skill have yet to be fully explained. The purpose of this work is to evaluate the sensitivities of HSLC convection’s mode, structure, and dynamics to low-level shear vector magnitude and lapse rates (or, equivalently in this case, CAPE) by systematically varying these parameters through a matrix of idealized simulations.

It will be shown that increased shear in the 0-1 km layer leads to the development of a larger number of near-surface vortices and strong low-level updrafts in simulated QLCSs, thus providing more opportunities for the intensification of near-surface vortices via stretching. Additionally, it will be shown that steeper 0-3 km lapse rates—and thus, increased 0-3 km CAPE—promote stronger low-level updrafts and embedded supercellular features within the simulated QLCSs, again increasing the likelihood that near-surface vortices will be intensified.

The goal of this work is to determine the mesoscale and storm-scale precursors leading to near-surface vortexgenesis within HSLC environments and how they are sensitive to relevant environmental parameters. Combined with existing forecasting techniques, these findings will help operational meteorologists anticipate convection that exhibits an increased likelihood of producing severe straight-line winds or tornadoes.