This doesn't happen often, but it just happened in Fairfield, Idaho. Snow rollers are a phenomena that requires a lot of factors to happen simultaneously. Fortunately for us, they did and Idahoan Dan Robbins captured a picture of it. 

The National Weather Service office in Boise shared this pic also and Wikipedia explained better than I can what it takes for a snow roller to appear.

The following 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.
  • Under this thin layer of wet snow there must be a substrate to which the thin surface layer of wet snow will not stick, such as ice or powder snow.
  • The wind must be strong enough to move the snow rollers, but not strong enough to blow them apart.
  • Alternatively, gravity can move the snow rollers as when a snowball, such as those that will fall from a tree or cliff, lands on a steep hill and begins to roll down the hill.

If you just can't get enough of snow rollers, here you go.