A warm front has a much shallower slope than the cold front overtaking it, so the warm, stable air behind it is lifted quite slowly over the colder air. At about 6,500-16,500 ft (2-5 km) an altostratus may form from water droplets, which may be below freezing temperature, or supercooled. From the ground this altostratus looks white or slightly blue and watery. It may form a continuous sheet, as in the picture on the left, or look as though it is made from soft fibers. Altostratus is light, and the sun is often visible through it, although the cloud may also be thick enough to hide the sun. Rain or snow may fall. Altostratus may not cover the whole sky, but it frequently does. Clouds of other types may be visible at its edges or beneath it.

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