[funhog]

we were skiing up on Tincan today and the hillside was scattered with pinwheels large and small. I believe this was the first significant snowfall in 2 weeks.

I believe Tremper when he says :

[Gary Brill]

Pinwheels or sunballs tend to pick up relatively fresh snow most easily. In each revolution they tend to pick up that snow down to some boundary, either the wet snow-dry snow interface, or in spring conditions down to the frozen part of the snowpack. The amount of snow that is picked up is about the depth that would want to slide as a wet snow slide.

If conditions are still ripe for these slides - that is if the surface is still wet - another way of gauging this is to take a pole and pull your basket laterally through the new snow. The damp snow should separate.

I doubt that wind would start pinwheels, but warm wind or just warm temperatures will on steep slopes or beneath trees or rocks where warm temperatures cause the snow to fall from them.

Old pinwheels where the surface is no longer moist just indicate it was once warm. The snowpack, if crusted or more cohesive may at this point in time have stabilized to a degree. The question then goes back to structure of the snowpack.

[Valdez Telehead]

FH...You mentioned graupel falling like snow, blowind in your face in your other report. This is indicative of warm air aloft and rain changing to snow at lower elevations. Perhaps in this lies your answer as to why pinwheel were forming up higher, or much wamer air aloft.

[funhog]

Thanks!

I wish I had my camera. The pinwheels start zone was tundra and not the rock bands or tree wheels. When we had skied over the terrain, we did not set off any pinwheels on our ski cuts. I've seen formation of pinwheels in both of those situations, but I'd never seen pinwheels here before like this. Dewam said he'd seen this situation here before. Most of the terrain where we were at was 20 to 30. There might be some bit steeper stuff. But the pinwheels were found all through the terrain.
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It's all about fun....

[Gary Brill]

At those angles, it would have to have been a warm wind.

[funhog]

When I was out skiing today, it occurred to me the pinwheels I poked and prodded were all very soft. Like they hadn't been frozen. Possibly they rolled on all aspects and the wind disintegrated those on the other aspects preserving those on what could the leeward side of the wind.

Thanks for helping me learn about snow!
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It's all about fun....

[BradA]

Ed LaChapelle's Secrets of the snow has some good info on this.