GNFAC Avalanche Advisory for Thu Mar 11, 2010

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

Although yesterday's snowfall was like lipstick on a pig, sometimes a little goes a long way.  My partner and I found good skiing yesterday on northerly aspects in the northern Gallatin Range on Mt Wheeler where the new snow seemed much deeper.  Why?  This new snow was sitting on several inches of faceted snow that formed on the old snow surface during recent warm sunny days and clear cold nights.  Additionally a new layer of surface hoar formed and was preserved on many northerly aspects.  With yesterday's snow, these new weak layers were preserved and will become a future problem if more snow comes.  See a video and photo of this future instability.

On southerly aspects we found a thick supportable crust formed by recent warm weather.  Unfortunately warm weather has not significantly strengthened the snowpack, and faceted snow near the ground on these southerly aspects seemed worse with exposure warm weather because these crystals are experiencing a transitional phase.  For now they are damp, funky, and weak, and I don't trust them.  A layer of surface hoar 1.5-2 feet deep persists and deserves a careful stability evaluation because it has gained strength on some slopes but not on others.  Overall the snowpack is thin and weak, and my partner yesterday said it looks more like a snowpack during hunting season than the snowpack of mid March.  Human triggered avalanches are possible, and one on Mt Jefferson in the Centennial Range yesterday (photo1, photo2) is a good reminder of this fact.  For today, throughout the entire forecast area, the avalanche danger is rated MODERATE.

New Beacon Park: Are you skiing or riding near West Yellowstone?  If so, consider testing your beacon skills at a new beacon park near the old airport where you can search for one or multiple beacons pre-placed in the snow and switched on/off by a control panel.  Look for it by orange snow fence and signage just south of the snow cross track.  For more information on beacon parks, visit: http://bit.ly/dqXrFM

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.