The Stratus cloud Stratus clouds are uniform gray clouds that usually cover the entire sky. They can form when very weak, upward vertical air currents lift a thin layer of air high enough to initiate condensation. Stratus clouds also form when a layer of air is cooled from below to its dewpoint temperature and water vapor condenses into liquid droplets.
Stratus clouds look like a layer of fog that never reaches the ground.
Precipitation rarely falls from true stratus clouds since the upward vertical motion needed for precipitation is very weak, but light mist and drizzle can sometimes accompany stratus clouds.