Height of base: 1,500 to 10,000 ft Colour: Dark grey. Shape: A thick, diffuse layer covering all or most of the sky. Other features: Sun or moon always blotted out. Accompanied by moderate or heavy rain or snow, occasionally ice pellets. Although classed as a medium cloud, its base frequently descends to low cloud levels. May be partly or even totally obscured by stratus forming underneath in precipitation.