1. cumulonimbus cloud
Wikipedia definition
2. Cumulonimbus cloudCumulonimbus (Cb) is a towering vertical cloud (family D2) that is very tall, dense, and involved in thunderstorms and other inclement weather. Cumulonimbus originates from Latin: Cumulus "heap" and nimbus "cloud". It is a result of atmospheric instability. These clouds can form alone, in clusters, or along a cold front in a squall line. They can create lightning and other dangerous severe weather.
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