Cirrostratus cloud

Common card · No. 395683

Cirrostratus () is a high-altitude, very thin, and generally uniform stratiform genus-type of cloud. It is composed of ice crystals, which are particles of frozen water. Cirrostratus is difficult to see and can produce halos. These optical effects are caused when the cloud takes the form of thin cirrostratus nebulosus. The cloud has a fibrous texture with no halos if it is thicker cirrostratus fibratus. On the approach of a frontal system, the cirrostratus often begins as nebulous and turns to fibratus. If the cirrostratus begins as fragmented of clouds in the sky it often means the front is weak. Cirrostratus usually lies above 5.5 km (3.4 mi; 18,000 ft). Its presence indicates a large amount of moisture in the upper troposphere. Clouds resembling cirrostratus occasionally form in the lower stratosphere over the polar regions of Earth. Polar stratospheric clouds can take on this appearance when composed of tiny supercooled droplets of water or nitric acid. Cirrostratus clouds sometimes...

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