The North Cascades Highway was the scene of a rare sighting last week when Washington state maintenance crews found naturally-occurring snow doughnuts. The state's avalanche forecaster and control technician, Mike Stanford, said they are rare.
Stanford said "It's formed by a clump of snow falling off of a cliff or a tree into the snow pack. And if the conditions and temperature are just right, as gravity takes over, it pulls the snow down, and it rolls back on itself."
"Usually the center collapses and it creates what we call a pinwheel," he said, adding the one he saw last week was the largest one he's ever seen, with an 8" hole and 26" tall.
source: http://www.npr.org
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