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Special conditions are required to produce a snow roller, a cylindrical roll of snow that grows larger as it is blown down a hillside. A smooth crust of old snow becomes covered with a layer of light new snow, followed by rapid warming and strong winds.
A small piece of moist, sticky snow may be picked up by the wind and sent rolling, leaving behind a shallow track marking its path. As it rolls, it collects more snow and becomes cylindrical in shape, often with a hole extending lengthwise through the center. The largest snow rollers grow to about one foot (30 centimeters) in diameter. © University Corporation for Atmospheric Research.