Illustration of cirrostratus clouds, thin, generally uniform clouds, composed of ice-crystals, capable of forming halos. When thick enough to be seen, they are whitish, usually with no distinguishing features
Illustration of cirrus clouds, which are characterized by thin, wisplike strands, often accompanied by tufts, leading to their common (non-standard) name of mare's tail. Cirrus clouds are formed when water vapor freezes into ice crystals at altitudes above 8000 meters (26,000 ft). Due to the sparse moisture at a high altitude, they tend to be very thin