Alto clouds are used to predict weather changes in 6 to 12 hours. An Altostratus cloud usually covers the whole sky. The cloud looks gray or blue-gray. The sun or moon may shine through an Altostratus cloud, but will appear hazy. An altostratus cloud usually forms ahead of storms with continuous rain or snow.
Altocumulus clouds are grayish-white with one part of the cloud darker than the other.
Altocumulus clouds usually form in groups. If you see Altocumulus clouds on a warm, sticky morning, be prepared for thunderstorms by late afternoon. Low clouds, called stratus clouds, are at altitudes up to 6,500 feet . These clouds form a solid sheet or layer of cloud mass. Stratus clouds are uniform gray in color and almost cover the entire sky.