Archived Advisory for Sat Mar 29 2008

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Is this Mark Staples with the Gallatin National Forest Avalanche Advisory issued on Saturday, March 29, at 7:30 a.m. Bridger Bowl, in partnership with the Friends of the Avalanche Center, sponsor today’s advisory. This advisory does not apply to operating ski areas.

MOUNTAIN WEATHER

Snow continues. As of 6 a.m. the Bridger Range has received 7 inches, the Gallatin and Madison Ranges have received 4-5 inches, and the mountains around Cooke City and West Yellowstone have received 7-9 inches. Unfortunately strong ridgetop winds of 20-50 mph from the west and southwest have accompanied this snowfall. Temperatures this morning are in the mid teens F and will stay there throughout the day under mostly cloudy skies. Winds will decrease to 15-30 mph and be mostly from the west. Another 2-3 inches of snow will accumulate today with most falling near Cooke City.

SNOWPACK AND AVALANCHE DISCUSSION

The Bridger Range, the northern Gallatin and northern Madison Ranges:

Yesterday on Bridger Peak, Karl Birkeland and his partner found a weak layer and triggered an avalanche on a steep non wind-loaded slope. No one was injured. This avalanche ran on a thin layer of small faceted crystals formed during a brief period of clear weather. People have been skiing and riding all over the Bridger Range without finding a similar weak layer. Generally the snowpack is strong and slopes similar to the one that slid have a low danger rating, but a low danger doesn’t mean “no” danger. Keep up the good work and continue to exercise safe travel in avalanche terrain: only expose one person at a time and watch them from a safe location, make sure everyone carries rescue gear which they know how to use, and constantly look for signs of instability.

See pictures of this avalanche at:

http://www.mtavalanche.com/photos/photos.php

Watch a video clip at:

http://www.youtube.com/watch?v=sx_NsDcNIB4

On Thursday, my partner and I rode and skied around Buck Ridge just south of Big Sky. We found mostly stable conditions within deeper layers of the snowpack. Instabilities were confined to the new snow, and we were able to trigger an avalanche 10 inches deep on a 37 degree, wind-loaded slope. Instabilities such as these quickly gain strength, but they need time without additional loading. Today that loading will continue with very strong winds, and widespread wind slabs will easily fracture under the weight of a skier or rider. Today, wind-loaded slopes will have a CONSIDERABLE avalanche danger if they are steeper than 35 degrees and a MODERATE avalanche danger if they are less steep. Slopes untouched by the wind will have a LOW danger.

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

Yesterday I went to Cooke City with an avalanche forecaster from Switzerland. We observed bison, elk, coyotes, wolves, and deep powder, but we didn’t see many obvious signs of instability. Snow has accumulated everyday since Monday with an equivalent amount of water over 2.5 inches for the week. This is a lot of snow. The snowpack is supporting this new snow better than I expected, and weak layers of faceted snow, which we found 2-3 feet deep, required moderate to hard force to fracture in our stability tests. Because the snowpack is highly variable, areas of weaker snow can still be found as illustrated by the avalanche Karl and his partner triggered in the Bridger Range. I would carefully every slope before skiing or riding on it and give extra caution to slopes with wind deposited snow. Strong winds this morning are forming slabs which will probably produce human triggered avalanches. For today, all wind-loaded slopes have a CONSIDERABLE avalanche danger. Non wind-loaded slopes have a MODERATE avalanche danger.

Doug will issue the next advisory tomorrow morning at 7:30 a.m. If you get out in the backcountry give us a call or email with your observations. You can reach us at 587-6984 or email us at mtavalanche@gmail.com

LAST ADVISORY5

Our 126th and last avalanche advisory of the season will be issued next Sunday, April 6th.