Current Advisory

GNFAC Avalanche Advisory for Wed Dec 17, 2014

Good morning. This is Doug Chabot with the Gallatin National Forest Avalanche Advisory issued on Wednesday, December 17 at 7:30 a.m. Today’s advisory is sponsored by Lone Peak Brewery and Outlaw Partners. This advisory does not apply to operating ski areas.


Mountain Weather: 

Snow graced our entire area with 6-7 inches falling around Big Sky and 2-3 inches everywhere else. Under cloudy skies temperatures are in the teens and winds are west to southwest at 10-20 mph with gusts of 30 in Hyalite. Snow flurries will end this morning and skies will be mostly cloudy with mountain temperatures reaching the mid-20s. Tomorrow looks to be sunny and my fingers are crossed for more snow later this week.


Snowpack and Avalanche Discussion: 

Bridger Range   Gallatin Range   Madison Range  

Lionhead area near West Yellowstone   Cooke City

The snow that just fell is 5-7% density powder which will greatly improve the skiing and riding without adding a lot of weight to stress the weak layers. I toured up Mt. Blackmore in Hyalite yesterday while Mark was riding around Cooke City. We both found that the weak facets at the ground are still a problem in isolated locations, but they are not breaking in our stability tests (snow profiles). Conversely, in and around Beehive Basin skiers reported some collapsing and are still getting a few stability tests to propagate fractures, a sign of instability. Although the snow structure is similar in our advisory area, the snow depth and rate of strengthening is uneven.

Snowfall since this weekend fell onto a variety of surfaces, not all of them good.  Some slopes were blanketed with small-grained facets or feathery surface hoar before the new snow fell making the new/old snow interface the most unstable part of the snowpack (video).

For today natural avalanche activity will be rare, and other signs of instability (collapsing and cracking) will only be sporadic, but the snowpack still demands a bit of investigation. Weak facets at the ground or under the new snow are the problem, especially if they are under a wind slab (video, photo). For today the avalanche danger is rated MODERATE throughout southwest Montana since it is still possible to trigger slides. Be wary of wind-loaded slopes near the ridgelines where thin soft slabs may have formed.


Mark will issue the next advisory tomorrow morning at 7:30 a.m. If you have any snowpack or avalanche observations drop us a line at mtavalanche@gmail.com or call us at 587-6984.


AVALANCHE EDUATION and EVENTS

Take a look at our Education Calendar for all our classes being offered.

TONIGHT: Avalanche Awareness and Beacon Practice, Wednesday, December 17, 6:30-8:30 p.m. at Beall Park, Bozeman

Avalanche Awareness (1-hr) at the Yellowstone Association in Gardiner, Thursday, December 18, 6:00-7:00 p.m.

Snowmobiler Introduction to Avalanches with Field Course

West Yellowstone: Dec 18 and 19, 2014: https://www.ticketriver.com/event/12955

Five hours of lectures are followed by a full day field course. Topics covered include: avalanche terrain recognition, the affect weather has on avalanche hazard, the development of the mountain snowpack, decision making skills, and basic search and rescue procedures.

Snowmobiler Rescue Course, Cooke City, December 27, 0800-1200. Register here: https://www.ticketriver.com/event/13721


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