- The ground must be covered by a layer of ice to which snow will not stick.
- The layer of ice must be covered by wet, loose snow with a temperature close to the melting point of ice.
- The wind must be strong enough to move the snow rollers, but not strong enough to move them too quickly.
- Sometimes gravity can move snow rollers, for example when snow falls from a tree and rolls down a hill.
My friend's town is not very hilly but it definitely gets strong winds These snow rollers were forming along the flat ground.
Anyway it is a wonderful sight, and just looking at it makes me feel less hot and sweaty. I have seen real snow, just not for a long time. I am glad I was not there when it was so cold, but I look forward to visiting her soon.