thumb|upright=1.35|Snow roller in [[Rocky Mountain National Park]]
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. 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:
- There must be a relatively thin surface layer of wet, loose snow, with a temperature near the melting point of ice.
Because of this last condition, snow rollers are more common in hilly areas. However, the precise nature of the conditions required makes them a very rare phenomenon.
Gallery
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File:Snow Roller.jpg|Snow roller with a gear-like shape from Rocky Mountain National Park, Colorado
File:Rolling snow.JPG|Snow roller in the Giant Mountains, in the Czech Republic near Poland
File:Snow rollers in Venus PA, USA.jpg|Snow rollers formed overnight during high winds in Venus, Pennsylvania
File:snowroller.jpg|A snow roller in Cincinnati, Ohio, United States
File:Schneeringe1 Foto Kathrin Spiegler.JPG|Snow rollers leaving tracks in the snow
File:Snow roller Illinois.jpg|Snow rollers at Lincoln Christian College, Illinois
File:Umgeworfene Schneerige 4 Foto Olaf Parnieske.JPG|Snow rollers in Saxony-Anhalt, Germany
</gallery>