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 that it often appears as
a wavy billowy layer of cloud, 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.