What are those rolls of snow in a farm field?

Those cylinder-shaped masses of rolled-up snow are called “snow rollers.” Some appeared after the pre-Christmas storm, but they are uncommon in the Midwest. (The last time someone told us they saw snow rollers was in February 2003.) While they may look like someone was rolling snow to make a snowman, you won’t see any footprints in the snow as these rolls form naturally.

The formation of snow rollers requires just the right weather conditions. They form when strong winds consistently blow across a snow-covered field. The field is covered with an icy crusty snow layer upon which fresh snow will not stick. On top is a layer of snow that is sticky, similar to good snowman-making snow, so the snow can stick to the roll as it moves, being pushed by the wind. This loose, wet layer of snow cannot be too deep, maybe a couple of inches at most. If the snow is too deep, it will be hard for the wind to move it along.

As in building a snowman, an initial “seed” roller needs to be started. In some way, the wind starts a small mass of snow moving. Then as the wind moves this seed roller along, it collects snow, gets larger and larger, forming a log shape as it moves downwind.

Snow rollers range in size from the equivalent of eggs to small barrels, but the average size is about 10 to 12 inches in diameter. Sometimes there may be a hole running lengthwise through the entire snow roller.

Category: Phenomena
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