Cirrostratus cloud
Cirrostratus clouds belong to a class characterized by a composition of ice crystals and often by the production of halo phenomena. They appear as whitish and usually somewhat fibrous veils, often covering the whole sky and sometimes so thin as to be hardly discernible. These clouds are of high altitude (20,000–40,000 ft or 6,000–12,000 m). Compare cirrostratus with other stratus cloud formations at lower altitude: altostratus, nimbostratus, and low altitude stratus clouds.