Clouds from which Cumulonimbus may form

(Section 2.3.10.5)

Cumulonimbus most commonly evolves from:

• Cumulus congestus (Cb cumulogenitus or Cb cumulomutatus) that was formed in the normal manner as described above.

Cumulonimbus also forms from:

• Altocumulus castellanus (Cb altocumulogenitus); the base of the Cumulonimbus is unusually high
• Stratocumulus castellanus (Cb stratocumulogenitus)
• Transformation and development of a portion of Altostratus or Nimbostratus (Cb altostratogenitus or Cb nimbostratogenitus)

In the majority of these cases, the transformation into Cumulonimbus passes through the Cumulus congestus stage.