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Altostratus is a cloud belonging to a class characterized by a generally uniform gray sheet or layer, lighter in color than nimbostratus and darker than cirrostratus. Means "high spread out." Compare also with lower altitude stratus clouds.

Altostratus is caused by a large air mass that is lifted then condensed, usually by an incoming frontal system.

Altostratus clouds can be found over wide-spread areas.

Altostratus clouds are potentially dangerous, because they can cause ice accretion on aircraft.