The visible satellite imagery (see loop below) is from a sunny, hot, and humid day. A few puffy cumulus clouds formed through the afternoon. Just south of the area, the cloud fields were a little more congested, forming bands across middle Tennessee. One of these bands of clouds grew just tall enough to break through the stable "cap" in the atmosphere and formed a brief thunderstorm. The visible loop below shows how quickly this storm formed. Notice the shadows off to the east, thanks to the lower sun angle later in the afternoon. The corresponding radar imagery shows how quickly the rain within the cloud developed and then precipitated out.
This type of storm is called a single-cell thunderstorm, because it starts with one strong updraft, or lift within the atmosphere, forms rain drops in the cloud and then after these drops collect sufficiently, the rain gets heavy enough to fall back to the ground, effectively killing the updraft.