C_H = 5

(a) TECHNICAL SPECIFICATION

Cirrus (often in bands) and Cirrostratus, or Cirrostratus alone, progressively invading the sky; they generally thicken as a whole, but the continuous veil does not reach 45° above the horizon.

(b) EXPLANATION

(i) Cirrostratus invading the sky progressively but with its continuous part still less than 45° above the horizon.

(ii) The veil of the Cirrostratus may be preceded by Cirrus clouds, often in long filaments (Cirrus fibratus), or shaped like commas (Cirrus uncinus), frequently arranged in bands crossing a part of the sky and seemingly converging towards one point or towards two opposite points of the horizon (variety radiatus).

(iii) Cirrus may also have a form resembling a fish skeleton (variety vertebratus).