Scattered showers and thunderstorms are nothing to write home about this time of year, but they're darn cool to look at on 3D weather radar, especially when they collapse right in front of a radar site.
The storms in southwestern Virginia this afternoon are your run-of-the-mill popcorn storms that you see in the late spring and summer months. They pop up due to daytime heating and last for about half an hour before the "rain out," so to speak. They're fun to watch on radar, especially because they're usually not harming anyone.
The GIF begins with the thunderstorm reaching maturity, right before the updraft (rising, unstable air) begins to choke off. As the updraft stops due to a lack of unstable air and water loading, the thunderstorm collapses and a burst of heavy rain and wind rushes towards the ground in the downdraft (sinking, stable air)
Once the bulk of the precipitation hits the surface and the downdraft starts to spread out as an outflow boundary, you can see it clear out all the fuzzy returns near the surface, which were caused by the bugs and birds showing up on radar. It's easier to see this on normal 2D radar.
The outflow boundaries from this and other nearby storms will determine how many other storms form in the Roanoke area this afternoon. That's the whole story of scattered springtime/summer thunderstorms — they're truly scattered and it's almost impossible to predict exactly where and how many will pop up. Once one storm forms, its outflow boundaries will cause a chain reaction, sparing one town and drenching the one next door.
[Images via Gibson Ridge and Wunderground]