GNFAC Avalanche Advisory for Wed Mar 10, 2010

The Bridger, Madison and Gallatin Ranges, the Lionhead area near West Yellowstone, the mountains around Cooke City and the Washburn Range:

Like putting lipstick on a pig, the inch of new snow is a feeble attempt at sprucing up the backcountry.  It's all for show. 

Before the snowfall last night, the snow surface consisted of facets and surface hoar (photo) on all but the most southern aspects.  These layers are now lightly coated with a trace to one inch of snow preserving this layer.  But this won't be our primary avalanche concern until we get more snow.  Down in the pack 1.5-2 feet deep we still have surface hoar (photo) breaking clean in our stability tests, although its taking more force to initiate a fracture.  A snowmobiler triggered, but was not caught, in a small avalanche on Mt Jefferson in the Centennial Range yesterday (photo1, photo2). Although slightly outside our forecast area, the snowpack here is similar to the conditions near West Yellowstone. It broke on a southeast facing slope near the ridge and looks to be a few feet deep.   Even deeper in the snowpack are the bigger, raw sugar sized facets that formed in December.  In the Bridger Range and around Hyalite and Big Sky these got moist which will increase their strength when they freeze again.  But we're still digging down to the ground in our snowpits to check this out for ourselves.

Without substantial new snow or wind-loading adding stress to our snowpack, the avalanche danger is in a holding pattern.  Strengthening is happening, but it's a slow process. As the snowmobiler on Jefferson found out, avalanches are still possible, especially on the weak layer buried two feet under the surface.  For today, throughout our entire forecast area, the avalanche danger is rated MODERATE.

I will issue the next advisory tomorrow morning at 7:30 a.m. If you get out in the backcountry let us know what you find.  You can reach us at 587-6984 or email us at mtavalanche@gmail.com.