Supercell thunderstorms are the most violent of all thunderstorm types, and are capable of producing damaging winds, large hail, and tornadoes. These large storms develop rotating updrafts ("mesocyclones"). A lowering of the cloud base may form beneath the mesocyclone and develop into what is known as a "wall cloud" as moist air is pulled up into the storm. If you'd like to learn much more about supercell thunderstorms, take a look at our Structure and Dynamics of Supercell Thunderstorms page. We also have a write-up on the differences between wall clouds, shelf clouds, scud clouds, and funnel clouds.
Below is a photograph of a wall cloud over Bowling Green on June 4 (thanks to Jason Darnall for forwarding his friend's picture to us). NWS Doppler radar detected the mesocyclone within the storm, and spotters were reporting the rotating wall cloud, along with funnel clouds, as the storm moved from Butler County into Warren County. In addition to the radar data and the eyewitness reports, NWS Louisville meteorologists also knew that the environment was conducive to tornado development. Indeed, a Tornado Watch had been issued for the area about five hours earlier. So, at 7:16pm CDT a Tornado Warning was issued for southern Butler County and northwestern Warren County. It was followed by a Tornado Warning at 7:32pm CDT for the city of Bowling Green and eastern Warren County since the storm continued its threat to develop a tornado. Fortunately, damage with this storm was restricted to some downed trees.
Head over to our YouTube Channel to take a look at a time lapse of this storm as seen from WKU.