Cirrostratus clouds are thin, higher level clouds. The name cirrostratus is Latin for "curl and spread out," or "curl" and "layer," which aptly describes how they appear in the sky. Cirrostratus clouds are often difficult to see and, when spread extremely thin, appear as more of a lightening of the sky than a cloud.
Cirrostratus clouds are composed of extremely thin, fibrous layers. The ice crystals that these clouds are composed of cause the light to create a halo effect around the sun or the moon when they shine through them. Cirrostratus clouds are usually layered horizontally in various thicknesses, covering the sky in vast sheets that range in color from light grey to white. Occasionally cirrostratus clouds may appear banded, with the area between the bands composed of thinner layers. The edges of cirrostratus clouds are typically uneven, but they may sometimes appear straight or clean. When cirrostratus clouds move lower in altitude, they form altostratus clouds, which are thicker. You can tell the difference between the two by looking for your shadow. If you can see it on the ground, the cloud above is a cirrostratus.
Cirrostratus clouds are usually formed by the spreading and eventual joining of cirrus clouds. This occurs as cool, dry air encounters warmer, moist air. Due to their high altitude, cirrostratus clouds are made up of ice crystals. Cirrostratus clouds may be indicators of impending rain or snow storms because they often represent a warm front coming in. However, they do not produce precipitation.
Clouds are classified based on the height at which they form as low, middle or high clouds. Cirrostratus clouds belong to the high family of clouds, which typically form between 20,000 and 42,000 feet above sea level. These clouds in particular form above 23,000 feet.
There are different types of cirrostratus clouds. Cirrostratus nebulosus clouds are unchanging in appearance, with no discernable features. These are the clouds that create halos around the moon or sun. Cirrostratus fibratus clouds are patchy and visibly fibrous, sometimes surrounded by cirrus clouds. Cirrostratus undulates clouds are distinguished by their wavy ripples and duplicatus clouds consist of more than one layer.