Mammatus clouds (DI02036) Photo by Ben Foster
Mammatus clouds are pouchlike formations protruding from the underside of cumulonimbus clouds. They are formed by downdrafts in which the air is cooler than the surrounding air. Their name is derived from the Latin word mamma, meaning breast. Though often observed in severe thunderstorms, mammatus do not produce severe weather themselves.
copyright University Corporation for Atmospheric Research