Cirrus

Wispy-looking cloud belonging to a class characterized by thin white filaments or narrow bands and a composition of ice crystals. These clouds are of high altitude (20,000-40,000 feet or 6000-12,000 meters).

Cirrus (Ci) A principal high-level cloud type (cloud genus), appearing as a detached clouds in the form of white, delicate filaments or white or mostly white patches or narrow bands. These clouds have a fibrous (hair-like) appearance, or a silky sheen, or both. Because cirrus elements are too narrow, they do not produce a complete circular halo.

(abbrev. CI) High-level clouds (16,000 feet or higher), composed of ice crystals and appearing in the form of white, delicate filaments or white or mostly white patches or narrow bands. Cirrus clouds typically have a fibrous or hairlike appearance, and often are semi-transparent. Thunderstorm anvils are a form of cirrus cloud, but most cirrus clouds are not associated with thunderstorms.