M5 Clouds: Altocumulus (Ac) progressively invading the sky
Semi-transparent altocumulus in bands,
[both of which are] progressively invading the sky; these generally thicken as a whole.
or
altocumulus, in one or more continuous layer (semi-transparent or opaque),[both of which are] progressively invading the sky; these generally thicken as a whole.
Additional Views:
Notes: These gradually spread from one part of the horizon, often passing overhead, and may eventually reach the opposite horizon. These clouds generally thicken and usually appear thickest towards the direction from which they first appeared. The clouds often lie in parallel bands and may be in one or more layers.
