CUMULONIMBUS CLOUDS

A principal cloud type; the ultimate stage of development of Cumulus clouds. Cumulonimbus clouds are very dense and very tall, commonly 5 to 10 miles in diameter, and sometimes reaching heights of 12 miles or more. The upper portion is at least partly composed of ice crystals, and it often takes the form of an anvil or vast plume. The base of the cloud is invariably dark and is often accompanied by low, ragged clouds. Also commonly called Thundercloud, Thunderhead, Thunderstorm. Also see Cloud.