Altocumulus Clouds (Middle Cloud Group)
Picture from UCAR Digital Image Library
Picture by A.K.Entingh
Altocumulus clouds are grayish-white with one part of the cloud darker than the other.
Altocumulus clouds usually form in groups and are about as wide as your thumb when you hold up your hand at arm's length to look at the cloud.
If you see altocumulus clouds on a warm humid morning, it means there is significant heat and moisture in the atmopshere. There is a high likelihood of thunderstorms by late afternoon.