Roll Cloud, Shelf Cloud

November 25, 2011

RollCloudinCompton06-25-06b_stitch (2)

Shelf cloudPhotographers: Top Photo - Claude Oesterreicher; Right Photo - Jimmy Hamilton
Summary Author: Claude Oesterreicher; Jimmy Hamilton; Jim Foster

November 2011 Earth Science Picture of the Day Viewer's ChoiceThe top photo showing a fierce looking roll cloud bearing down on a community in Compton, Illinois was taken during the late afternoon on June 26, 2006. Roll clouds and shelf clouds are found near the leading edge of thunderstorms and form when relatively cool air, from the storm’s downdraft, forges ahead into the warm, moist air that’s feeding the storm. The main difference between roll clouds and shelf clouds (both are called arcus clouds) is that a roll cloud is detached from the parent thunderstorm, whereas a shelf cloud (right) is affixed to the base of a cumulonimbus cloud. This roll cloud had more bark than bite when it barreled through Compton, but approximately 10 mi (16 km) away, a small funnel cloud descended outside the village of Sublette, Illinois. Fortunately, there were no injuries and damage was minimal.

Roll Cloud Photo: A two-photograph panorama taken from my front porch in Compton, Illinois at 4:30 p.m.
Shelf Cloud Photo: Taken at Highway A75, south of Dumfries, U.K. on June 12, 2011.