Nimbostratus are low level clouds, typically dark gray in color and associated with light to moderately falling precipitation. Low clouds are almost always comprised of water droplets since their bases generally lie below 6500 feet (2000 meters). However, when temperatures are cold enough, these clouds may contain ice particles and snow.

Because of the falling precipitation, the sun or moon is not visible through nimbostratus, unlike with cirrostratus clouds, where the sun or moon can be seen. Cloud bases are often difficult to accurately determine, since a layer of fog commonly forms beneath and around the bases of these clouds.