A cumulonimbus cloud near Swifts Creek, Victoria, Australia. Cumulonimbus are so named because they combine the characteristics of cumulus clouds (puffy in nature) and nimbus clouds (causing precipitation). They are typically around 30,000-50,000 ft (10,000-15,000 m) in height, and commonly produce precipitation and lightning. Cumulonimbus clouds occasionally become severe thunderstorms, and, if rotation is present in the atmosphere, can become supercells, producing high winds, heavy rain, hail, and rarely tornadoes. Fortunately, this only happens in a small fraction of cases; most cumulonimbus produce innocuous showers or thundershowers.
Recently selected pictures: Ice storm leaves, Mackerel sky, Lightning over Romania, More...