Cirrus (Ci)

Type: High-level cloud

Height of cloud base: 17,000-35,000 ft

Cloud colour: Composed of ice crystals, therefore white.

Cloud shape: Delicate hair-like filaments, sometimes hooked at the end; or in denser, entangled patches; or occasionally in parallel bands which appear to converge towards the horizon.

Other cloud features: The remains of the upper portion of a cumulonimbus is also classified as cirrus.