SPOKANE, Wash. — Many KREM viewers have sent us photos of what look like large snowballs near their homes in the Inland Northwest. Some have even asked us to explain the phenomenon.
What one viewer called "the snow equivalent of tumble weeds" are actually snow rollers. They are extremely rare due to the unique combination of snow, wind, temperature and moisture needed to create them, according to the National Weather Service.
Snow rollers form with light, sticky snow and strong – but not too strong – winds. Some are also formed by gravity, according to the National Weather Service.
The surface layer of snow must be wet and loose, with some ice and powder snow underneath. Snow rollers also contain chunks of ice and other materials they pick up along the way as they roll along the ground.
Snow rollers can vary in size from several inches tall to several feet. In March 2009, a North Idaho resident sent photos to the National Weather Service of snow rollers that were between 18 inches and two feet tall.