May 22 - July 31
Investigating Lightning Flash Rates in Tornadic Environments
Ethan J. Kerr, Vanna C. Chmielewski, and Michael Stock
What is already known:
- Thunderstorm flash rates are related to the strength of the midlevel updraft.
- Lightning jumps, a statistical increase in flash rates, in supercells are often associated with increases in mesocyclone rotation.
- Lightning jumps often occur before the onset of severe weather, but the correlation between flash rates and tornadoes in different storm modes is less understood.
What this study adds:
- Lightning jumps occur frequently in both tornadic and rotating non-tornadic cells, though total lightning is higher in the tornadic cells by a statistically significant margin.
- Trends in flash rates before tornadogenesis in both supercells and QLCSs are similar.
- Lightning flash rates increase steadily preceding tornadogenesis, peaking at around 17 minutes before tornadogenesis.
Abstract:
Lightning jumps, or a rapid increase in total flash rate, often precede severe weather and mesocyclogenesis. While there is plentiful research comparing lightning flash rates and general severe weather, there is less research on temporal relationships between flash rates and tornadogenesis in mixed storm modes. This study analyzes the total lightning flash rates of several dozen rotating cells from 12 tornadic environments from the PERiLS NSSL Lightning Mapping Array (LMA) deployments and the Oklahoma LMA. Cells were defined and tracked by their flash extent density. Comparative analyses were made between tornadic and non-tornadic cells, isolated supercells and cells embedded in quasi-linear convective systems (QLCSs), weak (EFU, EF0-1) and strong (EF2+) tornadoes, and time periods before and surrounding tornadogenesis. In a sample of 25 non-EF0, non-cyclic tornadoes, 80% were preceded by a 2-sigma lightning jump; however, more lightning jumps occurred in non-tornadic cells. When comparing flash rates before 31 tornadoes to peaks in low-level rotation in 19 non-tornadic storms, the tornadic storms experienced more total lightning. In a larger sample of 49 tornadoes, lightning flash rates were found to have steadily increased before tornadogenesis, peaking at around 17 minutes prior to tornado formation. After that, flash rates remained fairly steady across the sample. The difference in the change in flash rates before and after the 17 minute mark was statistically significant, providing confidence that an increase in flash rates precedes tornadogenesis. These results offer motivation for more research on lightning characteristics surrounding the evolution of tornadoes with larger sample sizes in the future.