Thursday, December 13, 2007

 Good Morning. This is Mark Staples with the Gallatin National Forest
 Avalanche Advisory issued on Thursday, December 13th at 7:30 a.m. The
 Yellowstone Club, in cooperation with the Friends of the Avalanche
 Center, sponsor todays advisory. This advisory does not apply to
 operating ski areas.


 MOUNTAIN WEATHER

 Since yesterday, the southern Madison Range and the mountains around
 Cooke City received a trace of snow, but most of the advisory area
 remained dry. This morning, temperatures are in the single digits and
 winds are westerly at 10-20 mph. A shortwave trough embedded in a
 cool, moist northwest flow will move over today. Ridgetop winds will
 be 15 mph from the northwest and temperatures will warm slightly to 10
 degrees F. Today will be cloudy with 2-4 inches falling by tonight.


 SNOWPACK AND AVALANCHE DISCUSSION

 The Bridger Range and northern Gallatin Range:

 Strong winds over the past two days in the Bridger Range moved Mondays
 powder to the lee sides of ridgetops and lower elevation gullies.

 These winds formed stiff wind slabs. Yesterday the Bridger Bowl Ski
 Patrol reported that these wind slabs were more difficult to
 trigger than they were two days ago; however, you may still
 trigger an avalanche on wind-loaded slopes. For today, the
 avalanche danger is MODERATE on wind-loaded terrain steeper than 35
 degrees and LOW on all other slopes.


 The Northern Madison Range

 We are getting more and more reports of people playing in the
 mountains around Big Sky, and the snowpack is stabilizing. A weak
 layer of faceted snow, found 1-2 feet above the ground, had a
 difficult time supporting the load of a large storm early last week,
 but it has gained strength and adjusted to the load. Recent snowfalls
 have made great skiing and riding conditions, and they have not added
 significant stress to the snowpack. The exception will be steep,
 recently wind loaded slopes where avalanches are still likely. For
 today, the avalanche danger is CONSIDERABLE on wind-loaded terrain
 steeper than 35 degrees and MODERATE on all other slopes.


 Check out a video shot by Big Sky Snow Safety of a large avalanche
 last week on Lone Peak at:

 http://www.youtube.com/watch?v=e7Z9XshN7-Y

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

 Many large avalanches occurred early last week following heavy
 snowfall which fell on a layer of weak, faceted snow similar to
 that found in the northern Madison Range. In the southern Madison
 Range near the Taylor Fork and West Yellowstone this layer of
 faceted snow is especially weak and continues to show signs of
 instability in the form of collapsing and cracking of the snowpack.

 Scott saw these signs during an avalanche class on Sunday. A group
 skiing near Bacon Rind on Sunday found darned good skiing, but they
 observed these same signs of instability and limited their travel to
 slopes less than 28 degrees. Doug rode in the mountains around Cooke
 City, and he saw evidence of recent avalanche activity which occurred
 on this layer of faceted snow 1-2 feet above the ground.

 Stability tests can be confusing in these areas because this
 weak layer is slowly gaining strength and giving mixed results in
 the tests. The best indications of the continued weakness of this
 layer have been reports of collapsing and cracking of the snowpack
 which tell me human-triggered avalanches are still likely especially
 on wind-loaded slopes.


 For today, the avalanche danger is rated CONSIDERABLE on all
 wind-loaded terrain and MODERATE on all slopes without a wind load.

 Remember, a Moderate danger means its possible you can trigger
 a slide, so make sure every in your group carries rescue gear and
 travel one at a time through avalanche terrain.