GNFAC Avalanche Advisory for Wed Dec 18, 2013

Not the Current Forecast

Good morning. This is Doug Chabot with the Gallatin National Forest Avalanche Advisory issued Wednesday, December 18 at 7:30 a.m. A Montana FW&P Recreation Trails Grant sponsors today’s advisory. This advisory does not apply to operating ski areas.

Mountain Weather

Under partly cloudy skies temperatures are in the high twenties with ridgetop winds blowing southwest at 20-30 mph. Today clouds will increase as winds remain the same and temperatures climb into the mid-thirties. A cold front will arrive tonight and drop mountain temperatures into the single digits, but snowfall looks to be minimal with only 1-2 inches falling.


Bridger Range   Madison Range   Gallatin Range 

Lionhead area near West Yellowstone   Cooke City

Traveling in avalanche terrain is tricky right now. Natural and human triggered slides have been reported every day for over a week with folks remotely triggering slides up Hyalite (photo) on Monday and near Ross Peak in the northern Bridger Range on Saturday (photo). Remote triggers are when you trigger an avalanche from a distance or even below a slope. They are extra scary because you do not have to be on the slope, just nearby. Look at our Photos and Video pages to grasp the scope of avalanche activity over the past seven days.

The snowpack structure is unstable and not very supportive. Weak, faceted snow is found in the bottom 1 ½ feet of the snowpack (snowpits). Snowpacks less than three feet deep are the weakest. Eric and I found this in Lionhead (video) and stayed clear of a low-angled wind-loaded slope while digging our snowpit. Soft and hard wind slabs are avalanching on top of these facets and I recommend steering clear of any wind-loaded slope. 

Mark and his partner are in Cooke City. Their concerns are similar to everywhere else: (1) wind slabs, and (2) facets near the ground. A snowmobiler triggered slide on Sheep Mountain on Monday (photo) and a recent cornice triggered avalanche illustrate the danger. Furthermore, Cooke City has a layer of surface hoar (large feathery crystals) buried two feet under the surface.  On most slopes it is not breaking, but on a few it is. Dig for it because someone will inevitably find one of these “few” slopes and get taken for a ride.  

Mark, Eric and I are unanimous in not trusting the snowpack to behave in a predictable way. Although the odds of triggering an avalanche are decreasing, we are traveling in the backcountry as though it’s likely. Recent activity, remote triggers, and collapsing/cracking is bull’s-eye data that cannot be ignored no matter what our stability tests say. Keeping this in mind, the avalanche danger today is rated CONSIDERABLE on wind-loaded slopes and MODERATE on all others.


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.


BACKCOUNTRY SKIERS AND RIDERS NEEDED FOR MSU SURVEY

This project aims to collect GPS location information and survey responses from backcountry skiers and riders to better understand what types of terrain decision we make. The focus is on backcountry skiers and riders of all abilities and experience. You need not be an expert backcountry skier to participate in this research. For more information and to sign up: www.montana.edu/snowscience/tracks


SNOWMOBILE AVALANCHE EDUCATION

The Canadian Avalanche Association produced a series of videos titled “Throttle Decisions” on avalanche safety for snowmobilers. Mark’s blog post outlines the topics.


EVENTS/EDUCATION

COOKE CITY: TODAY, 9:30 a.m. Avalanche Awareness Clinic, Community Center.

GARDINER: Thursday, December 19, 7-8 p.m. Avalanche Awareness, at the Yellowstone Association in Gardiner. Call Zachary for more info at: 406-848-2850.

WEST YELLOWSTONE: Snowmobiler Intro to Avalanches w/ Field Course; 19 and 20 December. Info and registration: https://www.ticketriver.com/event/7116

BOZEMAN: Saturday, December 21, 10:30-11:30 a.m. FREE Avalanche Transceiver Workshop, Bridger Bowl, next to the rental shop at Jim Bridger Lodge. NO registration required. Just show up.

WEST YELLOWSTONE: Sunday, December 29, 10 a.m., Companion Rescue Clinic for Snowmobilers, Pre-Registration is required.  https://www.ticketriver.com/event/9387


 

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