An Analysis of Observed Cold Pools in VORTEX-SE Supercells and Quasi-Linear Convective Systems

Many past severe weather field campaigns have focused on supercell thunderstorms over the Great Plains of the United States, leading to a deeper understanding of supercell dynamics in traditional tornadic environments which are often characterized by high CAPE and high vertical wind shear. However, there is a lack of supercell and linear-mode observations recorded in the less traditional environments of the southeastern United States. These environments (such as high vertical wind shear with low CAPE) produce supercells that may differ dynamically from Great Plains storms, and oftentimes produce hybrid storm modes such as embedded supercell clusters and quasi-linear convective systems (QLCS) circulations. The Verification of the Origin of Rotation in Tornadoes Experiment – Southeast (VORTEX-SE) field project hopes to remedy this lack of in-situ data by observing supercells and QLCS circulations that occurred in Northern Alabama and Southern Tennessee during 2016 and 2017.

During the VORTEX-SE field campaign, 16 Texas Tech University “StickNet” probes observed the equivalent potential temperature and virtual potential temperature deficits within the cold pools of supercell thunderstorms and QLCSs. These measurements were motivated by previous observational studies which showed tornadic storms tend to have weaker temperature deficits and higher buoyancy in their flanking downdraft regions than nontornadic supercells. However, there are no studies that consider the cold pool deficits between tornadic and non-tornadic segments of QLCS events.

This study will compare the potential temperature deficits and cold pool evolution of tornadic and nontornadic supercells and QLCS circulations sampled during VORTEX-SE. We will also show that the cohesiveness of a cold pool edge and the rate of buoyancy decrease may also be important for tornadogenesis by virtue of the implied baroclinic vorticity generation. A QLCS on 30 April 2017 showed relatively smaller equivalent potential temperature deficits associated with two mesovortices, one of which was weakly tornadic and another which was tornado-warned but nontornadic. The tornadic mesovortex was also associated with one of the largest virtual potential temperature gradients within that QLCS, thereby differentiating the tornadic and nontornadic mesovortices. This feature has been identified in at least one other VORTEX-SE QLCS event. Additionally, a tornadic QLCS on 10 March 2017 produced the largest deficits of the event (as large as 19 K) at the probe nearest to the tornadic activity. This is generally contrary to the results found in observational studies of supercells, although it is not known if the cold pool near the tornadoes still contained positive buoyancy. These results will help establish a climatology of southeastern supercell and QLCS cold pool deficits and characteristics, components of which may shed light on mechanisms for tornadogenesis.