C_H = 1

(a) TECHNICAL SPECIFICATION

Cirrus fibratus and sometimes Cirrus uncinus, not progressively invading the sky.

(b) EXPLANATION

(i) Cirrus corresponding to C_H = 1 most often occur in the form of nearly straight or more or less curved filaments (Cirrus fibratus); more rarely, they are shaped like commas topped with either a hook or a tuft that is not rounded (Cirrus uncinus).

(ii) Cirrus fibratus and uncinus commonly appear in the same sky with Cirrus of other species; the code figure C_H = 1 may be used only if the sky cover of Cirrus fibratus, uncinus or a combination of these clouds is greater than the combined sky cover of other Cirrus species.

(iii) Cirrus, coded C_H = 1, is not progressively invading the sky.