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Gallery: Reading the Clouds

Cumulonimbus

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(Image credit: NOAA)


As they develop vertically upward they may go from small, fair weather clouds to large, boiling monsters called cumulonimbus, also called thunderheads.

Such clouds are most often associated with cold fronts: When a mass of cool, dry air pushes into a warm, moist air mass, the heavier cool air acts like an atmospheric plow and pushes the warm air up into violent thunderstorms. High winds aloft can make the cloud's top into a flat anvil-like shape and their bottoms are usually very dark.

These clouds can forecast some of the most severe weather including torrential downpours, vivid lightning, hail and even tornadoes.

Mammatus Clouds

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(Image credit: NOAA Photo Library, NOAA Central Library; OAR/ERL/National Severe Storms Laboratory (NSSL))


Clouds that look like hanging bulges from the skies are called mammatus clouds. More often than not, references statr that such clouds are a forbearer of severe weather, but actually, just the opposite is true: These clouds are formed by sinking air and are sometimes seen after a potent thunderstorm; they signal that a storm is retreating, not approaching.