Phenomenon requires specific conditions
By Duane Friend, Photo by Diane Dugan
When I was growing up, back in the time when grade schoolers were allowed to play in the snow during recess, we would make “snow forts,” making several large snowballs maybe three feet wide.
Today, our warmer winters and changes in policies have made this just a memory. While making snowballs is not as possible or acceptable as it used to be, sometimes nature will create something similar.
A couple of weeks ago I got a message from an Extension colleague in the west central part of the state. They were asking about what appeared to be snowballs that had shown up in several people’s yards. Being the weather geek I am, I enthusiastically let the Extension person know what they had were snow rollers!
Snow rollers are rare in Illinois, but more common in Canada and points north. Weather conditions must be unique for snow rollers to occur. Snow must be fresh and moist, and there must be strong winds. In addition, the ground must be clear of standing plants and residue. Temperatures near or slightly above freezing are ideal.
Snow rollers are not snowballs. As the name implies, they are more in the shape of a tube. Strong winds will make some snow start to drag across the surface. Additional snow collects on the moving snow, creating a small sheet. This sheet continues to roll, gaining more snow. Once the roller is too heavy for the wind to move, it stops. They often will have a hollow center.
Fresh snow on top of older, crusty snow or ice also makes snow roller creation easier. Most snow rollers are only a few inches in diameter, although in very rare instances they can get up to two feet!
If you ever have a chance to see snow rollers for yourself, take lots of pictures, because you may not see them again for a long time!