Nimbostratus

urn:aero:airm:1.0.0:ConceptualModel:Subjects:Meteorology:Nimbostratus

Grey cloud layer, often dark, the appearance of which is rendered diffuse by more or less continuously falling rain or snow, which in most cases reaches the ground. It is thick enough throughout to blot out the Sun. Low, ragged clouds frequently occur below the layer, with which they may or may not merge.

Source: WMO International Meteorological Vocabulary,