are rounded, smooth, sack-like protrusions hanging from the underside of a cloud. May occur with cirrus, altocumulus, altostratus, stratocumulus and cumulonimbus. Mammatus clouds often accompany severe thunderstorms, but do not produce severe weather; they may accompany non-severe storms as well. See HP storm, LP storm and supercell.

Hanging protuberances, like pouches on the under surface of a cloud. In the case of cumulonimbus, mamma generally appear on the underside of the anvil, but have been viewed on other parts of the cloud.

These clouds appear as hanging, rounded protuberances or pouches on the under surface of a cloud. With thunderstorms, mammatus are seen on the underside of the anvil. These clouds do not produce tornadoes, funnels, hail, or any other type of severe weather, although they often accompany severe thunderstorms.