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GNFAC Avalanche Advisory for Fri Mar 5, 2010

Not Current Advisory

Good Morning. This is Mark Staples with the Gallatin National Forest Avalanche Advisory issued on Friday, March 5, at 7:30 a.m.  Javaman, in cooperation with the Friends of the Avalanche Center, sponsors today's advisory.  This advisory does not apply to operating ski areas.

Mountain Weather: 

Overnight a trace of snow fell near Big Sky and 2-3 inches fell in the southern Madison Range and the mountains near West Yellowstone.  This morning temperatures were in the mid to low 20s F with NE and E winds blowing 5-10 mph.  A low pressure system over Utah and Colorado will spin moisture towards southwest Montana this morning without much accumulating snowfall.  By late this afternoon any snowfall should end with 1-2 inches accumulating near Cooke City and possibly in the mountains near Bozeman.  Winds will remain light blowing 5-10 mph from the NE, and temperatures will be near 32 degrees F.

Snowpack and Avalanche Discussion: 

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

As more time passes since the last significant snowfall in mid February, and March sunshine becomes more intense, spatial variability increases.  This variability is most profound when evaluating the strength of a layer of either surface hoar or near surface facets buried 1-2 feet deep.  On many slopes this layer either never formed or has gained noticeable strength, while on others, especially shaded slopes, it remains sensitive.  Faceted snow deeper in the snowpack and closer to the ground also exhibits variability, but mapping this variability is more difficult as this layer has a full season's worth of weather and snow layers on top of it.  Also, this layer is less affected by changes in weather because it is buried so deeply.

Skiers have used cornices to test slopes and in several cases produced large avalanches.  One occurred in Hyalite Canyon on Monday.  Another similar one occurred yesterday just south of Saddle Peak in the Bridger Range (photo 1, photo 2).  It may be tempting to assume that these avalanches occurred only because a large cornice dropped onto the slope and a skier's weight would not be a sufficient trigger.  This assumption is dangerous, and sometimes suckers us into a false sense of security as the first person on a slope may not trigger it.  It will lie waiting until tickled in just the right spot which is often an area of thin snow near buried rocks.  The slide in Hyalite shows many potential trigger points (photo).

Without significant snowfall to stress buried weak layers, stability is generally improving but instabilities linger.  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.

Eric 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

29th Annual Pinhead Classic on Saturday, March, 6th.  "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 12th to Friday, March 14th

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

 

Audio: 
Audio for Mar 5, 2010