This is a photograph of altocumulus clouds.
Click on image for full size
Courtesy of UCAR Digital Image Library
Altocumulus clouds (weather symbol - Ac), are made primarily of liquid water and
have a thickness of 1 km. They are part of the Middle Cloud group (2000-7000m
up). They are grayish-white with one part of the cloud
darker than the other. Altocumulus clouds usually form in groups.
You can distinguish an altocumulus cloud from a stratocumulus cloud by pointing
your hand toward the cloud. If the cloud is about the size of your thumbnail,
then it is altocumulus.
Altocumulus clouds in view on a warm humid morning indicate thunderstorms by
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