An Investigation Between Tornadic and Non-Tornadic QLCS Vortices using Blended MRMS Products

Quasi-linear convective system (QLCS) tornadoes have become an active area of research over the last several years. Through numerical simulations, it is theorized that QLCS vortex formation occurs near the surface in a quick response to heterogeneities along the baroclinic zone at the leading edge of the system. There exist a few conceptual models that describe QLCS vortex formation. The process of downward vortex line tilting occurs as storm outflow forces existing baroclinic vorticity downward, creating subsequent vorticity couplets within the updraft. Upward vortex line tilting occurs after a surge in outflow that allows the development of a vorticity couplet on both ends of the bowing segment. The subsequent gust front begins to tilt baroclinic vorticity along the leading edge, promoting a cyclonic-only vortex. The release of horizontal shearing instability along the leading edge of the system acquires energy from the ambient flow, subsequently producing vertical vorticity at the near surface that allows mesovortexgenesis to take place. These conceptual models describe vortex formation resulting from forced lift along the gust front in an area of enhanced baroclinity. Given the rather complex storm-scale dynamics and brief nature of QLCS vortex formation, is it possible to detect signatures in the minutes leading up to QLCS mesovortexgenesis and subsequent QLCS tornadogenesis using currently operational systems?

The Multi-Radar Multi-Sensor (MRMS) systems has a few experimental algorithms that can observe storm-scale dynamic features in real time taking advantage of the quality of the WSR-88D network. Incorporating WSR-88D radars surrounding a target QLCS can provide a more complete three-dimensional image that captures storm-scale characteristics at both the low and upper levels, blended onto a 1 km and 500 m grid space. This work highlights testing of currently operational (e.g., dual-pol products and azimuthal shear) and experimental MRMS products (e.g., divergence shear and total shear) that aid in detecting QLCS vortices in both pre-tornadic and tornadic phases. A total of 107 tornadic and 139 non-tornadic vortices are examined over 13 QLCS events from 2019 through 2022. This presentation will highlight that a combination of intense low-level cyclonic shear collocated with strong divergence in the mid-to-upper levels surrounding the vortex is a unique signature 15 minutes prior to a QLCS tornado report. Tornadic vortices are associated with lower ZDR below 3 km AGL and higher KDP below 3 km AGL relative to non-tornadic vortices throughout the duration of their lifetime. However, high variability in all operational and experimental products exists for tornadic vortices retained in the dataset, indicating that the processes involved in QLCS tornado formation vary on a case-by-case basis.