Cloud Classification


General description

Grey or whitish, or both grey and whitish, patch, sheet or layer of cloud which almost always has dark parts, composed of tessellations, rounded masses and rolls, and which may or may not be merged.

Most of the regularly arranged small elements have an apparent width of more than five degrees, when observed at an angle greater than 30 degrees above the horizon. This is the approximate width of three fingers held at arm's length.

Common subdivisions

The most common species is Stratocumulus stratiformis, being rolls or large rounded masses arranged in an extended sheet or layer. The elements are more or less flattened.

Less common are Stratocumulus lenticularis and castellanus. These exhibit similar characteristics to the Altocumulus version of these species.

Stratocumulus sometimes forms from the spreading out of Cumulus. When the top of a Cumulus cloud reaches a higher stable (warmer) layer, it may spread out to form a patch of Stratocumulus; Stratocumulus cumulogenitus (Cumulus being the mother-cloud) is the resultant cloud.

Another form of Stratocumulus cumulogenitus can occur in the evening if convection ceases leading to the domed cumulus summits flattening out.

Distinguishing Sc from other genera

Stratocumulus differs from Altocumulus in that most of the regularly arranged elements of Stratocumulus have an apparent width of more than five degrees, and its height usually does not exceed 8500 ft.

Stratocumulus differs from Cumulus in that its elements usually occur in groups or patches and generally have flat tops (stratiformis species). If the tops are in the form of shallow domes they rise, unlike those of Cumulus, from merged bases.

Stratocumulus differs from Stratus, Altostratus and Nimbostratus in that it shows the presence of non-fibrous elements, either merged or separate.

Associated precipitation

Stratocumulus rarely produces precipitation; in the event it does, it will be very light rain or snow, or drizzle – (the association of drizzle with Stratocumulus is a non-WMO convention).

Stratocumulus stratiformis
Stratocumulus stratiformis (Photo: P. Toomey)
Stratocumulus stratiformis (Photo: P. Leigh)
Stratocumulus cumulogenitus
Stratocumulus cumulogenitus, with Cumulus (Photo: J. Darnley)