A snow roller is a rare meteorological phenomenon in which cylindrical snowballs are formed naturally as chunks of snow roll down hill or are blown along the ground by wind, picking up further snow along the way, in much the same way that the large snowballs used in snowmen are made. They can be as small as a tennis ball, but they can also be bigger than a car. Most snow rollers are a few inches or centimeters wide.
Alternative names for snow rollers include: snow bales, snow donuts, snownuts and wind snowballs. Unlike snowballs made by people, snow rollers are typically cylindrical in shape, and are often hollow since the inner layers, which are the first layers to form, are weak and thin compared to the outer layers. The inner sections can easily be blown away, leaving what looks like a doughnut or Swiss roll.
Several conditions are needed for snow rollers to form:
Snow rollers formed overnight during high winds in Venus, Pennsylvania
A snow roller in Cincinnati, Ohio, United States
Snow rollers at Lincoln Christian College, Illinois
Snow rollers in Saxony-Anhalt, Germany