C_H = 3

(a) TECHNICAL SPECIFICATION

Cirrus spissatus cumulonimbogenitus.

(b) EXPLANATION

(i) The coding C_H = 3 is used only when at least one Cirrus cloud present in the sky provides direct or indirect evidence of having originated from a Cumulonimbus. This Cirrus spissatus cumulonimbogenitus may be accompanied by Cirrus spissatus of doubtful origin, by Cirrus castellanus, Cirrus floccus, Cirrus fibratus or Cirrus uncinus.

(ii) Observers, by keeping a continuous watch of the sky, may be able to witness the development of Cirrus spissatus from the upper part of a Cumulonimbus. Often, however, they have no direct information about the origin of Cirrus spissatus. There may nevertheless be sufficient indirect evidence to indicate, with reasonable certainty that a Cirrus spissatus present in the sky originated from a Cumulonimbus.

(iii) Cirrus spissatus cumulonimbogenitus frequently reveals its origin by the hairy or frayed appearance of its edges, by its general anvil-like shape, or by its optical thickness that is often sufficient to veil the Sun, obscure its outlines or even hide it.