C_M6 Ac from spreading out of Cu

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Gallery
© R.K. Pilsbury	© R.K. Pilsbury
© F. Norton	© F. Norton
© F. Norton	© R.K. Pilsbury

On some occasions, the upward growth of cumulus clouds is arrested on reaching medium cloud levels. The top of the cumulus cloud then spreads out to form altocumulus C_M6. The top left photograph shows the early stages of this type of formation. The same cloud some time later, when the spread of the altocumulus had become much more extensive is shown top right. Cirrostratus is also seen above the altocumulus and cumulus.

The set of three images (middle and bottom left) show another example of this type of altocumulus development.

Occasionally, after a temporary spreading out, upward growth is resumed in places, so that that altocumulus appears on the side of the cumulus. The upward growth can be seen in the photograph at bottom right. Altocumulus C_M6 can also occur on the side of cumulonimbus.

Because of the way in which it is formed, C_M6 occurs in patches. These patches are fairly thick at first and the under surface may appear rippled. However, later they tend to thin out and break into separate elements. Altocumulus never has the fibrous structure, silky sheen or whiteness of the anvil of cumulonimbus.

Classification
Description: Altocumulus resulting from the spreading out of Cumulus or Cumulonimbus.	Designation: CM=6 (C3)
	Latin name: Altocumulus cumulogenitus (Ac cugen) or Altocumulus cumulonimbogenitus (Ac cbgen).

Related pages: Cloud classification | C_L guide | C_M guide | C_H guide | Cloud index