Page "Cirrus cloud" Paragraph 41

Cirrostratus clouds can appear as a milky sheen in the sky or as a striated sheet.

They are sometimes similar to altostratus and are distinguishable from the latter because the sun or moon is always clearly visible through transparent cirrostratus, in contrast to altostratus which tends to be opaque or translucent.

Cirrostratus come in two species, fibratus and nebulosus.

The ice crystals in these clouds vary depending upon the height in the cloud.

Towards the bottom, at temperatures of around to, the crystals tend to be long, solid, hexagonal columns.

Towards the top of the cloud, at temperatures of around to, the predominant crystal types are thick, hexagonal plates and short, solid, hexagonal columns.

These clouds produce halos very commonly, and sometimes the halo is the only thing that indicates the presence of the cloud.

They are formed by warm, moist air being lifted slowly to a very high altitude.

When a warm front approaches, cirrostratus clouds deepen and lower into altostratus, and rain usually begins 12 to 24 hours later.