A rare winter phenomenon, a snow roller is formed when the wind blows wet snow into a roll. Three weather conditions must occur simultaneously and in the proper order for snow rollers to take shape. First, there has to be sufficient accumulation of light, fluffy snow. Secondly, once the snow has stopped falling, the temperature has to rise above the freezing mark, making the snow sticky. Finally, a strong wind is required to roll the snow up in layers. If the wind is strong enough, the moving ball of snow becomes cylindrical, often with a hole through it lengthwise. Snow rollers range in size from that of eggs to small barrels. Their tracks are sometimes several metres long and less than one centimetre deep. Recorded snow roller sightings have occurred in Regina on December 25, 1993, and near Willow Bunch in February 2001.