Snow rollers are a phenomenon that happens when the snow is just the right texture, temperatures are perfect and the winds are at just the right speed. Snow rollers are extremely rare to see in their true form and there are many meteorologists that have never experienced this privilege. This is due to the fact that although snow rollers do occur they never stay formed long enough for many to see them. Like the conditions of the weather you have to be at the right place at the right time to actually see this rare event.
How snow rollers form
Snow rollers mostly occur on a snow covered hill but also occur in open flat fields. When they occur in open fields it is a very rare phenomenon as there is no gravity to move them, just the wind pushing them along. Snow rollers act in the same way that you would make a snowman the difference is the snow is not well packed and is not moved by force of hand but by wind or gravity.
The center of a snow roller stays soft and fluffy and as the snow roller grows they usually collapse onto themselves which is one of the reasons they are so rare. Field snow rollers are the rarest and if you ever see one you are very lucky. Conditions for snow rollers have to be perfect.
Prerequisites for snow rollers
There is a prerequisite for a snow roller to happen. The underlying snow must be frozen hard enough that the snow can move easily over its surface, the fresh snow must be the consistency of wet loose snow, the temperature must be at melting point and the wind has to be strong enough to force this snow to move unless it is moved by gravity. In fields the wind can’t be too strong but must be just right to start this snow rolling slowly.
Snow rollers formed by gravity
Although the snow rollers that are formed by gravity need the same prerequisites for snow texture as those in the fields they do not need the wind to form. Any action can start them rolling such as a piece of snow that start rolling down the side of a hill from the friction of a car passing by. However they do form in the same way which is very soft and fluffy in the center and when they become too heavy these too will collapse onto themselves. Hill snow rollers are not as rare to see as those you find in a field.
Snow rollers formed in fields
These are the snow rollers that are the most elusive and are generated by the wind, not to strong or not to weak but just right. The wind picks up the snow to start forming the first circle of the ball. The wind forces this ball to keep moving over the flat surface picking up more snow as it goes. These types of snow roller grow as large as two feet in diameter but the center remains very weak.
The larger the snow roller becomes the more weight is pushed on the center which eventually collapses onto itself and what you see after the collapse is somewhat the shape of a doughnut. This is why field snow rollers are so very rare to see. You have to be there when the conditions are just perfect and this phenomenon is taking place. Snow rollers can be seen very easily once they have collapsed. These are not rare in forming but rather they are rare in seeing them happen. After the right type of weather it is not difficult to see donuts spread all over a farmer’s field. You may even be lucky enough to see a few of them still intact. The rarity comes from the actual forming of the snow roller itself.
Snow rollers can occur anywhere in the world where there is snow, wind and the right snow conditions. They occur in the US as well as Canada where winter blankets the country. So if you are very lucky and the conditions are right you may just witness the birth of one of these snow rollers. When you do you are privy to one of nature’s wonderful quirks in the form of a snow roller.
