C_M7 Ac at more than one level

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Gallery
© C.S. Broomfield
© C.S. Broomfield
© C.S. Broomfield

Besides being used to specify altocumulus together with altostratus or nimbostratus, the code figure C_M7 is used to describe patches, sheets or layers of altocumulus at two or more levels.

These patches, sheets or layers may be of either generally thin altocumulus (although thick enough in places to mask the sun or moon completely), or altocumulus which is thick throughout.

The elements of the altocumulus do not change continually, nor do the clouds progressively invade the sky.

In the top photograph the lower grey layer was estimated to be at 8,000 ft and the higher white layer at 12,000 ft. In the middle photograph the layers are estimated to be between 10,000 and 15,000 ft. The bottom photograph was taken when the sun was low in the sky and the difference in colouring shows the two layers quite distinctly. The base of the grey dark layer was estimated to be 8,000 ft and the upper white layer at 15,000 ft.

Code figure C_M=7 is also used to report other types of altocumulus. Refer to the pictorial guide for descriptions of other cloud types of C_M7.

Classification
Description: Patches, sheets or layers of altocumulus at two or more levels.	Designation: CM=7 (C3)
	Latin name: Altocumulus opacus (Ac op) or Altocumulus translucidus (Ac tr) [plus other varieties].

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