GNFAC Avalanche Advisory for Sat Mar 6, 2010

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

If there is enough snow to ski or ride, then there is enough snow to slide.  This concept needs to remain atop of our minds, despite the fact that we have not received significant snowfall in close to three weeks.  Dry spells tend to support an out of sight out of mind philosophy, making it easy to overlook signs of snow instability. Although the snow surface may not display obvious clues, digging 1-2 feet below the surface or all the way to the ground will reveal a different story.

Buried surface hoar continues to persist 1-2 below the surface and is consistently found on shady slopes protected from the sun and wind.  This weak layer has displayed an ability to produce clean, propagating fractures during stability tests, and should be studied and thoroughly considered before laying tracks on north facing slopes. Weak faceted crystals 1-2 feet below the surface can also be found on south facing slopes, although this layer is a bit more variable with its strength and distribution.  Digging a quick snowpit or two can help you determine if these layers exists, and a few stability tests will give you a good idea of their sensitivity.       

The most tenacious layer of the snowpack continues to be the facets near the ground.  This layer continues to display its capabilities of propagating and producing large avalanches with the proper amount of stress.  This was demonstrated on Monday when skiers triggered a large hard slab avalanche in the Flanders drainage of Hyalite Canyon and again on Thursday when another group of skiers triggered a very similar avalanche in Argentina Bowl south of Saddle Peak in the Bridger Range. (photo 1, photo 2).  Both of these avalanches were intentionally triggered with cornice drops and failed on the weak facets near the ground.  It is misleading to think that deep slab avalanches can only be triggered by large forces such as cornice drops or explosives.  Either one of these dangerous avalanches could have been triggered by a skier or snowmachine if tickled in the right place.

If you are heading into the backcountry this weekend keep one thing in mind, avalanches are still possible. The weakest slopes are likely shaded ones with the best skiing and riding conditions where careful evaluations of stability and terrain are essential.  For today human triggered avalanches are possible and 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. 

Avalanche Education & Events 

1. Bridger Bowl

29^th Annual Pinhead Classic on Saturday, March, 6^th.  "Carnival" is this year's costume theme, so come dressed up to race, socialize and win great prizes. Registration fee is $30 but gets you all sorts of cool stuff. Check out the website http://pinheadclassic.com for details. 

2. Bell Lake Yurt, Tobacco Root Mountains

Montana Backcountry Adventures - Level I Avalanche Course

Wednesday, March 12^th to Friday, March 14^th

For more info call 995-3880 or go to www.skimba.com