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

External link

• National Science Digital Library - Altostratus (http://www.nsdl.arm.gov/Library/glossary.shtml#Altostratus)