20 January 2008

 Good morning. This is Ron Johnson with the Gallatin National Forest
 Avalanche Advisory issued on Sunday, January 20, at 7:30 a.m. This 
 advisory does not apply to operating ski areas.

 MOUNTAIN WEATHER

 Since yesterday morning 6-10 inches of snow accumulated in the
 mountains around Bozeman and Big Sky. The mountains around West
 Yellowstone and Cooke City got 4-6 inches. Today a cold front combined
 with a moist weather disturbance will deposit 6-8 inches of snow in
 the Bridger Range. The mountains around Big Sky, Cooke City and West
 Yellowstone will get 4-6 inches. Northeasterly ridgetop winds will
 blow 10-20 mph and mountain temperatures will be near 0 degrees F.

 SNOWPACK AND AVALANCHE DISCUSSION

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

 On Friday, an avalanche buried and injured a snowmobiler near Cooke
 City. Yesterday, Doug and his partner investigated the slide. It
 released on a wind-loaded, south facing, 35 degree steep slope. The
 avalanche released on a layer of small grained faceted crystals buried
 3-6 feet deep. The slide was 100 feet wide and ran 1,100 vertical
 feet. 

 The layer of faceted crystals doesnt exist on all slopes. In fact,
 Doug didnt find it on slopes adjacent to the avalanche. Not knowing
 where this layer exists is scary. Unless you are willing to dig
 snowpits and look for this layer its best to assume it exists on all
 south-facing slopes. This layer will be especially active on
 wind-loaded slopes. A layer of faceted crystals buried 2-4 deep also
 exists on Lionhead, near West Yellowstone. Today, a CONSIDERABLE
 avalanche danger exists on all wind-loaded slopes. A MODERATE
 danger exists on non wind-loaded slopes.

 The Gallatin Range and Madison Ranges:

 Yesterday, ski patrollers at the Yellowstone Club used explosives to
 release an avalanche that broke 4-6 feet deep on a layer of faceted
 crystals near the ground. It fractured on a wind-loaded slope. Ski
 patrollers at Big Sky released several soft slab avalanches on
 recently wind-loaded slopes. Ice climbers in Hyalite Canyon noticed
 collapsing and cracking of the snow around their snowshoes. Skiers on
 Mt. Ellis found weak faceted crystals buried under 1-2 feet of
 recently deposited snow. They didnt see an obvious signs of
 instability because on the slopes they were skiing the new snow wasnt
 cohesive enough to form a slab. A widespread layer of faceted snow
 buried 2-4 feet deep continues to produce avalanches, and collapsing
 and cracking of the snow in the Gallatin and Madison Ranges. Today the
 avalanche danger remains CONSIDERABLE on all recently wind-loaded
 slopes and on non-wind-loaded slopes steeper than 35 degrees.

 Non-wind-loaded slopes that are less steep have a MODERATE avalanche
 danger.