Usually form in advance of storms that produce much widespread and continuous precipitation. Sometimes rolled out in parellel waves or bands with bases darker than other parts of the same cloud. Individual cumulus puffs should be about the size of the ball of your thumb when your hand is held at arms length. Can cover portions of or the entire sky. Only light drizzle or light snow grains fall from true stratus clouds.
Fog occurs when stratus clouds are in touch with the ground surface.
Very uniform cloud bases. These clouds contain more water and the cumulus puffs are larger than altocumulus. Appears in rows, patches or in rounded masses with blue sky visible between cloud elements. Sometimes occurs with the spreading out of cumulus clouds later in the day. Color ranges from white to dark gray.