C_H7 Cirrostratus covering the whole sky

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Gallery
© R.K. Pilsbury
© R.K. Pilsbury
© C.S. Broomfield

Code figure C_H=7, is only used when a veil of cirrostratus covers the entire sky. Although it may be relatively dense, the veil is sometimes so thin that it is barely visible. It may be distinguished from altostratus by its thinness, which allows shadows to be cast when the sun is not low in the sky, and that it often displays halo phenomena (top and middle photographs).

If the sun is bright, it may be difficult to see the halo around it (top photograph). However by covering the sun with the hand, it is usually possible to see any halo quite well.

It is sometimes difficult to discern cirrostratus through haze. Cirrostratus differs from haze, in that haze is opalescent or has a dirty yellowish to brownish colour.

If there are any gaps in the veil of cirrostratus through which the blue of the sky can be distinguished, the coding for C_H should be 8.

Cirrus at different levels, and cirrocumulus, may also be present.

The cirrostratus in the middle photograph is thin and featureless. In the bottom photograph a halo is not detectable. Any variations in the thickness of the cirrostratus are noticeable when the sun is low in the sky.

Classification
Description: Veil of Cirrostratus covering the celestial dome.	Designation: CH=7 (C2)
	Latin name: Cirrostratus nebulosus (Cs neb) or Cirrostratus fibratus (Cs fib).

Related pages: Cloud classification | C_L guide | C_M guide | C_H guide | Cloud index