When I first got these pictures from our maintenance crews on the North Cascades Pass (SR 2o), I assumed they had used Photoshop and were pulling my chain. I called to verify the validity of the pictures. The crews promised that these were indeed real, and that snow doughnuts are a naturally occurring phenomenon. I had never seen this type of thing before, so I asked around the office and it appears no one else has either. I decided to send the pictures to the media, who also thought we used Photoshop.
According to Mike Stanford from our WSDOT avalanche team, snow doughnuts are a natural occurrence in nature. We do not build them. They form when there is a hard layer in the snow and is then covered by several 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, and voila you have snow doughnuts.
As gravity pulls the clump down, the snow rolls down the hill, and 99.9% of the time the center of the rolling snowball collapses in on itself and creates what we call a "pinwheel". If it doesn’t roll down the
Stanford says he’s rarely seen it happen. The temperatures and snow conditions have to be just right. In 30-plus years of playing and working in the snow, this was the second time he had ever seen them. Snow doughnuts seemingly could grow very big if conditions permitted. The one seen in the photograph is about 24" in diameter.