An Overview of the Urban Impacts on Supercell Thunderstorms

On the night of March 2nd, 2020, an outbreak of severe weather occurred in the Southeastern U.S. After rapid intensification just east of Nashville, TN, one supercell associated with this outbreak spawned a number of significant tornadoes. Among these include the infamous EF-3 which tore through the heart of the city. As a result of how quickly the storm was modified, the alarm was raised only a few minutes prior to the storm’s entrance into the city. Disseminating life-saving warnings can sometimes prove difficult, given how smaller-scale systems can change quickly over time. In order to relay the best forecasts possible, a greater understanding of how the landscape and atmosphere of urban areas influence meteorology within the immediate region. Investigations performed on similar events where cities saw severe weather-related impacts have shown that the urbanized landscape may have had such an influence. This especially rings true for two key components on a localized scale- the Urban Heat Island (UHI) phenomena as well as the urban levels of the Atmospheric Boundary Layer (ABL). On one hand, UHIs can influence severe weather elements such as CAPE, while the surface roughness within the urban ABL can modify components such as wind shear.

This study aims to equip forecasters with an insight into the general impacts such urban-driven alterations can have on incoming supercell thunderstorms. To pinpoint a correlation, a number of events related to supercells tracking directly over urbanized areas will be selected. Recorded data from the events such as radar reflectivity products, temperature, and lightning observations will then be placed onto a map overlaying a given urban area. The data will then be analyzed to observe the supercell’s evolution as it passed over the sampled area. Next, the observations from each region will be compared to find similar traits, especially in terms of urban influences. It is expected that the analysis of the results will display a connection between supercell evolution and urban environments. All in all, by understanding the impacts of urban environments on supercell thunderstorms, forecasters can more effectively predict and disseminate timely warnings, especially regarding severe weather phenomena similar to the event which impacted Nashville.