Most commonly, rain clouds that produce a steady rain are referred to as nimbostratus clouds. These clouds appear low in the sky and are a medium to dark gray color. Sometimes stratus clouds are associated with a light drizzle.
Stratocumulus clouds almost never produce rain, although they can turn into nimbostratus clouds if conditions allow. Mammatus clouds and green clouds are normally associated with severe weather, including hail or tornados. High types of clouds, above 18,000 feet, are known as cirrus clouds. Clouds above 6,500 feet to 18,000 feet are called alto clouds. Clouds below 6,500 feet are mainly the stratus clouds that may indicate rain.