Snow rollers are a weird weather phenomenon that occurs only under perfect conditions. You have to have strong winds (but not too strong) and sticky snow (but not too sticky). They’re kind of a Goldilocks thing: everything has to be “just right.”

Check out this picture:

Snow Rollers, photo by Tim Tevebaugh

Snow Rollers, photo by Tim Tevebaugh

Further explanation can be found here: National Weather Service and Snow Rollers.