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.
Light mist or drizzle is sometimes associated with Stratus clouds. Stratocumulus clouds are low, lumpy and gray. Most form in rows with blue sky visible in between. Precipitation rarely occurs with Stratocumulus clouds, however, in frontal weather they may turn to Nimbostratus. Nimbostratus clouds are dark gray with a ragged base.