Clouds from which Cirrus may form

(Section 2.3.1.5)

Cirrus often evolves from:

• Virga of Cirrocumulus (Ci cirrocumulogenitus)
• Virga of Altocumulus ( Ci altocumulogenitus)
• Upper parts of Cumulonimbus (Ci cumulonimbogenitus)

Cirrus clouds may also form as a result of the transformation of non-uniform Cirrostratus by evaporation of the thinner parts (Ci cirrostratomutatus).