ALTOCUMULUS

Composed of flattened thick, gray, globular masses, this middle cloud genus is primarily made of water droplets. In the mid-latitudes, cloud bases are usually found between 8,000 and 18,000 feet. A defining characteristic is its layer effect, often with a wavy billowy appearance, giving it the nickname of "sheep" or "woolpack" clouds. Sometimes confused with cirrocumulus clouds, its elements (individual clouds) have a larger mass and cast a shadow on other elements. It may form several sub-types, such as altocumulus castellanus or altocumulus lenticularis Virga may also fall from these clouds.

White and/or gray patches, sheets, or lalyers of clouds generally with shading composed of rounded masses or rolls, which are sometimes partially fibrous or diffuse and which may or may not be merged. Altocumulus clouds exist in the mid level of the sky between 2 to 6 kilometers above the ground (in meteorology, the prefix alto is used with other cloud types to describe other mid-level clouds as well). They are one of four genera that are hybrids of cumulus clouds. [See also cumulus.]