A rolled-up, cylindrical mass of snow, rather common in mountainous or hilly regions. It occurs when snow, moist enough to be cohesive, is picked up by wind blowing down a slope and rolled onward and downward until it either becomes too large or the ground levels off too much for the wind to propel it farther. Snow rollers vary in size from very small cylinders to some as large as 1. 5 m long and more than 2 m in circumference.