Polarimetric Radar Signatures of Significantly Severe Left-moving Supercells

Left-moving (LM) supercells are capable of producing damaging winds, large hail, and even tornadoes in exceedingly rare cases. Their impact and capability for destruction is well-established; however, the existing research on LM supercells is extremely limited. This study evaluates over 100 significantly severe LM supercells (producing hail 2” or greater, winds 75 mph or more, or a tornado) and is the first study to conduct a comprehensive evaluation of the polarimetric radar presentation of a significant quantity of LM supercells. The majority of published work on LM supercells takes a case-study approach, examining only a few or even just a single storm. Additionally, most LM supercell research was conducted prior to the polarimetric upgrade to the WSR-88D radar network, a renovation that led to numerous studies on right-moving (RM) supercells. These radar studies have substantially improved scientific understanding of RM supercells, but similar work has not been done for LM supercells, leaving forecasters and researchers at a disadvantage regarding an entire class of impactful storms.

This study utilizes an automated detection algorithm - the Supercell Polarimetric Observation Research Kit optimized for LM supercells (Left-SPORK) - to quantify several polarimetric supercell signatures. The Z_DR arc area, Z_DR column area and depth, K_DP foot area, hailfall area, and K_DP-Z_DR separation vector are calculated for each case. Mean values are calculated and compared to those for significantly severe RM supercells in order to develop a baseline model of LM supercell radar presentation in the context of the widely understood RM supercell radar model. Significant differences found in the polarimetric signatures between the two models are highlighted.