They don’t appear very often but when they do, they get everybody talking – snow rollers!
A snow roller is a fairly rare meteorological phenomenon where snowballs are formed naturally as chunks of snow are blown along the ground by wind. Once they get moving, they pick up more snow along the way; it’s a lot like rolling snowballs to make a snowman. However, unlike snowballs made by people, snow rollers are usually cylindrical and are often hollow since the inner layers, the first layers to form, are weak and thin compared to the outer layers and can easily be blown away. Their hollow centre makes them look a little like a swiss roll… remember those?
Snow rollers have been seen to grow as large as one metre in diameter.
While most snow rollers are seen in wide open fields, every now and again we are treated to one where we can have a good look without jumping fences.
The basic ingredients still apply…
- The ground or, in this case, the windshield must be covered by a layer of ice.
- The layer of ice must be covered by wet, loose snow with a temperature near the freezing point of ice.
- The wind must be strong enough to move the snow rollers, but not strong enough to blow them too fast; ideal wind speed is about 45 km/h.
- Alternatively, gravity can move the snow rollers.
Because of this last condition, snow rollers are more common in hilly areas… or on windshields. Thank you for sharing Evelyn.