Do cities encourage warm-season thunderstorm formation and intensification?

Results of a radar-based, warm-season climatology of convection for several large cities in the Southeast U.S. are presented. In particular, we examine how the urban heat island augments convection in this thunderstorm-prone area that has seen substantial increases in population over the last two-to-three decades. The research utilizes National Weather Service Doppler radar composite reflectivity data from 1997-2006. We stratify the radar data according to specific “medium” and “high” reflectivity thresholds for the warm season (May-August), which are used to develop radar climatologies that illustrate “hotspots” of thunderstorm activity. Furthermore, these reflectivity thresholds can be employed as surrogates for strong (“medium” reflectivity) and severe (“high” reflectivity) thunderstorms, which can be used to do determine if the city is inducing more intense storms.

Additionally, we explore how the Atlanta urban region influences warm season (May through September) cloud-to-ground lightning flashes. Multiple years of flashes from the National Lightning Detection Network are mapped under different wind speed and direction combinations derived from cluster analysis. Overlays of these data in comparison to the radar climatology affirmed a consistent coupling of lightning and convective enhancement around the Southeast's largest city, Atlanta.