Height of base: 8,000 to 17,000 ft Colour: Greyish or bluish. Shape: A sheet of uniform appearance totally or partly covering the sky. Other features: Sometimes thin enough to reveal the sun or moon vaguely, as through ground glass. Objects on the ground do not cast shadows. May give generally light rain or snow, occasionally ice pellets, if the cloud base is no higher than about 10,000 ft.