A resident of St. Louis took an awesome time lapse of a strong thunderstorm rolling across his neighborhood yesterday. The storm bubbled up on the horizon before racing towards the camera, developing an awesome shelf cloud along the way.
The line of thunderstorms produced a couple of instances of wind damage to the west of St. Louis, but thankfully they weakened below severe levels before entering the most heavily populated areas.
The gnarly-looking, wedge-shaped cloud that comes over the neighborhood shortly before the video ends is called a shelf cloud. Shelf clouds form when a cool "bubble" of air from a thunderstorm (called the "outflow") moves across the surface along and just ahead of the storm. Warm, moist air rises up along the leading edge of the outflow, condensing below the thunderstorm as a shelf cloud. Most shelf clouds are ragged in appearance, but others like the one shown in the video look incredible.
The storms around St. Louis got a little more airtime than usual on the news due to the immense media presence in nearby Ferguson. Huffington Post's Amanda Terkel sent out this photo of the shelf cloud as it came across a highway near Ferguson:
— Amanda Terkel (@aterkel) August 21, 2014