Cloud Classification


General description

Transparent, whitish cloud veil of fibrous (hair-like) or smooth appearance, totally or partly covering the sky, and generally producing halo phenomena (a coloured ring or partial ring around the sun or moon with red on the inside and white on the outside).

At high angles Cirrostratus is never thick enough to prevent objects on the ground from casting shadows. However, when the sun is low on the horizon (below about 30 degrees), the longer light path through the cloud may reduce the light intensity such that shadows do not exist. Also at low sun angles, grey shading within the cloud may be apparent.

Common subdivisions

The species Cirrostratus fribratus shows a fibrous veil in which thin striations can be observed. This species may develop from Cirrus fribratus.

The nebulous veil of Cirrostratus nebulosis will show no distinct detail at all. It may be so thin that it is barely visible - the presence of a halo may be only indication of its existence. Conversely, it may also be relatively dense.

Distinguishing Cs from other genera

Cirrostratus is distinguished from Cirrus in that it occurs as a veil usually of great horizontal extent.

Cirrostratus is distinguished from Altostratus by its thinness, and that it may show halo phenomena. Except when the sun is low on the horizon, Cirrostratus does not prevent shadows being cast.

Associated precipitation

Cirrostratus is not associated with any precipitation.

cirrostratus nebulosus
Cirrostratus nebulosus
cirrostratus fibratus
Cirrostratus fibratus (Photo: P. Leigh)
cirrostratus fibratus
Cirrostratus fibratus with the sun low on the horizon
cirrostratus fibratus
Cirrostratus fibratus with an aerological diagram showing its vertical extent - approx 20,000ft (Photo: P.Toomey)