Snow Doughnuts

This was in last week's Seattle Times:

Stanford found frozen doughnuts of snow on the top of Washington Pass in the North Cascades this week when he was doing avalanche-control work.

At first he couldn't believe his eyes: Perfectly shaped doughnuts had rolled down the mountainside and frozen in place.

He said it's only the second time in his 30 years of working in the snow that he's seen anything like it.

The larger of the snow rollers, as they are commonly called, was about 24 inches tall, he said, large enough for him to put his head through the hole.

Stanford said snow rollers form when there is a hard layer on the snow, covered by several more inches of dense snow. "Then you add a steep slope and a trigger such as a clump of snow falling out of a tree or off of a rock face."

As gravity pulls a clump down, it usually rolls down the hill and collapses, creating what the WSDOT calls a pinwheel. Or it will not roll at all, and come down in an avalanche of snow. But if the snow is the perfect density and temperature, it rolls down leaving a hole in the center, Stanford said.

Strong, gusty winds also can be a factor, according to NOAA's National Weather Service office in central Illinois, where snow rollers have occurred.

As soon as the sun comes out and it warms up, the doughnuts would be gone, Stanford said Friday.

Click here to see the rest of the article and for a photo of a snow doughnut.

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