Cumulonimbus Clouds in sunset

Cumulonimbus (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 “accumulated” and nimbus “rain”. It is a result of atmospheric instability.  Photographer Corbis Premium

These clouds can form alone, in clusters, or along a cold front in a squall line. They create lightning through the heart of the cloud. Cumulonimbus clouds form from cumulus clouds (namely from cumulus congestus) and can further develop into a supercell, a severe thunderstorm with special features.