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GNFAC Avalanche Advisory for Tue Apr 6, 2010

Not Current Advisory

Good Morning. This is Mark Staples with the Gallatin National Forest Avalanche Advisory issued on Tuesday, April 6, at 7:30 a.m.  Bridger Bowl, in cooperation with the Friends of the Avalanche Center, sponsors today's advisory.  This advisory does not apply to operating ski areas.

Mountain Weather: 

Heavy snow is falling this morning in Bozeman with 2-3 inches in most areas.  Temperatures were in the high teens and low 20s F with ridgetop winds blowing 10-20 mph.  Last night winds blew from the E but shifted to the NW and W this morning.  Today temperatures should reach the upper 20s F and winds should remain the same.  Snow will continue with an additional 3-5 inches falling near Cooke City and 5-7 inches in all other areas by tomorrow morning.

Snowpack and Avalanche Discussion: 

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

Over the past 10 days in the Rocky Mountains there have been 7 avalanche fatalities (details), with 2 occurring in Montana.  Fortunately none have occurred in SW Montana, but snowpack conditions exist in the advisory area similar to areas where these fatal avalanches have occurred.  A weak layer of faceted snow, formed during dry weather from mid February to mid March, has been stressed by snow from recent storms.  This situation has led to many natural and human triggered avalanches.  Several notable ones occurred in past few days:

  1. Several avalanches occurred this weekend in the Bridger Range south of Bridger Bowl (photo1, photo2).
  2. A very large skier triggered avalanche occurred just outside the advisory area near Emigrant Peak in the Absaroka Mountains on Monday (photo).
  3. On Sunday a natural avalanche was observed in the northern Madison Range on a north facing slope near 10,000ft. This slide appeared to have been triggered by a falling cornice and broke 1-3 ft deep but broke at the ground in places.
  4. This weekend two avalanches occurred in the southern Madison Range. A group of skiers triggered one on a steep north facing slope near a ridge line at 9400 ft. It started as a wind slab 10 inches deep but stepped down another foot running 1000 vertical ft and 150 ft wide. They also observed a small natural avalanche nearby that slid on a 30-33 degree slope (photo) and experienced widespread collapsing and whumpfing.
  5. On Friday a group riding in the trees near Cooke City triggered a large avalanche. With their GPS unit they measured the width of the avalanche to be approximately 1000 ft.
  6. Another recent avalanche was reported near Cooke City on Mt Abundance near the Wilderness boundary.

These avalanches offer clear evidence of an ustable snowpack. The most disturbing aspects of this recent activity have been long distances over which these avalanches have propagated.  With more snow falling this morning at a rapid rate, the snowpack will remain near its breaking point.  Today human triggered avalanches are probable and the avalanche danger is rated CONSIDERABLE.  If heavy snowfall continues today the avalanche danger could rise to HIGH in areas with wind-blown snow.

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.

 

 

 

 

 

Audio: 
Audio for Apr 6, 2010