Snow rollers are nature’s snowballs, formed when high winds roll a chunk of snow along the surface, allowing it to accumulate more and more material. They occur relatively rarely because their appearance is the culmination of several specific meteorological factors. To form rollers, the ground needs to be icy, with a layer of loose, wet snow above the ice. And, of course, it needs to be windy enough to move the snow without being so windy that snow breaks up. In the photos above, the snow roller got too large for the wind to continue moving it, but the wind didn’t stop blowing. Instead, the snow roller became an obstacle to the flow and a horseshoe vortex formed at its base. The spinning of the vortex dug out the trench in front of and along the sides of the snow roller. This same effect is often seen on the windward side of trees in winter. (Photo credit and submission: S. Benton)