Radar Precursors to Severe Weather Reports in Left-moving Supercells

While much research has examined dual-polarimetric signatures of right-moving supercells, very little has been done with left-moving supercells. Given that left-moving supercells are thought to be disproportionate producers of large hail, understanding their internal dynamics is vitally important. This study examines differences and trends in the dual-polarimetric signatures of left-moving supercells to identify precursors to severe weather reports. A dataset of left-moving supercells associated with severe weather reports was created. These storms are processed with an automated analysis algorithm that identifies and quantifies the polarimetric signatures in each storm. A method for analysis of differences and trends in their dual-polarization signatures in the 30 minutes prior to a severe weather report is developed. ZDR columns and arcs are used to infer changes in storm and updraft strength. ZDR arcs show no statistically significant differences leading to a severe hail report. The increase in reflectivity magnitude over the 30-minute analysis period prior to a severe hail report is statistically significant. The key finding from this research is that ZDR columns show a statistically significant decreasing trend in both depth and areal extent leading to a severe hail report, which may be operationally valuable. Advisor: Matthew S. Van Den Broeke