Evolution of Shear Profiles Preceding Significantly Tornadic, Tornadic, and non-Tornadic QLCSs

Quasi-linear convective system (QLCS) tornadoes are difficult to predict with any confidence, especially more than a few minutes in advance. QLCS tornadoes have lower PODs and shorter lead times than supercellular tornadoes, and though they are disproportionately weaker tornadoes, they can still cause significant damage. Even significant QLCS tornadoes have poor verification statistics compared to supercellular tornadoes of similar strength. The Propagation, Evolution, and Rotation in Linear Storms (PERiLS) project was designed to increase knowledge of QLCSs, especially in the environment leading up to the severe weather. This analysis, which is funded by the PERiLS project, will examine the near-storm environment, with the goal of understanding how changes in the kinematic environment affect the prevalence of QLCS tornadoes.

This project uses NEXRAD Velocity Azimuth Display (VAD) data and its derived wind profiles to examine how the environment changes ahead of QLCS systems. Traditional upper air releases are too spatially and temporally sparse to use for this analysis, but VAD data is a widely accessible substitute. Environmental changes are examined for three different QLCS modes: significantly tornadic (QLCS that produced more than 5 tornadoes), weakly tornadic (QLCS that produced just 1 tornado), and non-tornadic (QLCS that produced at least 10 severe wind reports, but no tornadoes). To complement PERiLS field observations, the VAD analyses begin 4 hours prior to a QLCS passing over a radar site. Changes in shear and helicity across time for the 3 QLCS modes are tracked. In addition, since profiles with the same shear and helicity can behave differently, mean hodographs are examined for each subset of data, and hodograph changes are tracked over time. Preliminary analyses suggest that the size and shape of the hodographs vary significantly through the subset modes, and could be of use by forecasters performing mesoanalysis.

This analysis looks at QLCS systems that occurred in the Southeastern United States from the years 2005-2018, and data from this project will be compared to data collected during the PERiLS field campaign. Work continues on expanding the database to bring in null cases, as well as further stratifying the QLCS events by tornado count, tornado strength, and wind damage report count.