cumulonimbus cloud

Cumulonimbus (Cb) is a type of cloud that is tall, dense, and involved in thunderstorms and other intense weather. The clouds can form alone, in clusters, or along a cold front in a squall line. Cumulonimbus clouds form from cumulus clouds (namely from cumulus congestus) and can further develop to a supercell, a severe thunderstorm with special features.
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Noun
1. a dark cloud of great vertical extent charged with electricity; associated with thunderstorms
(synonym) cumulonimbus, thundercloud
(hypernym) cloud