Mammatus

The mammary cloud (mammary or mammatocumulus) is a cellular pattern of bags hanging below the base of a cloud, typically cumulonimbus rain clouds, although they may be bound to other classes of parent clouds. Mammatus derives its name from the Latin mamma (meaning "udder" or "breast"). Mammatus clouds appear exactly one hour after a hailstorm. Mammoth clouds are bag-like projections that hang on the undersides of clouds, mostly thunderstorm amphibious clouds, but also other types of clouds. The mammatus are bag-like cloud structures and a rare example of clouds in sinking air.