Predicting Tornadogenesis in Supercell Merger Events Using Cloud-to-Ground Lightning

Supercells are a unique and typically destructive type of thunderstorm that are responsible for nearly all violent (EF-3 or greater) tornadoes, as well as most significant (2 inches or greater) hail and significant (EF-2 or greater) tornadoes. In nearly half of all supercell cases, these storms experience merger events with other storm cells, which rapidly alters the dynamics and environment of the supercell. This can result in a wide variety of consequences, ranging from complete storm collapse to violent tornado production. Predicting this outcome can be particularly difficult in operational settings due to the current lack of quantifiable indicators in radar or surface analysis. However, numerous past studies have identified strong, observable relationships between cloud-to-ground (CG) lightning behavior and the strength, stage, and dynamics of thunderstorms. This study identifies correlations between CG lightning behavior and tornado production in supercell merger events. The lightning properties under investigation include strike time, location, polarity, multiplicity, and peak current, as well as the flash frequency, all of which are examined before, during, and after the merger event. Because the storm structure and the surrounding environment rapidly change during these events, anomalous behavior of these lightning properties may be indicative of a storm structure or environment that is favorable for constructive development and tornado production. This study quantifies these relationships over a large geographical scale, across a large set of cases, and within the specific scope of cell-supercell merger events. The results of this study may be particularly useful to operational meteorologists and forecasters who can use these statistical correlations to predict the tornadic potential of a supercell merger event, allowing for greater lead times when issuing warnings. The findings will also be of great interest to those researching storm structure, mesoscale dynamics, and tornadogenesis due to its implications on the roles that cell and supercell structure play in tornado production.