Altocumulus

This is a photograph of altocumulus clouds. Click on image for full size version (40K JPG) 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 late afternoon.