GNFAC Avalanche Forecast for Sun Dec 12, 2021

Not the Current Forecast

Good Morning. This is Alex Marienthal with the Gallatin National Forest Avalanche Forecast on Sunday, December 12th at 7:00 a.m. This information is sponsored by Montana State Parks, Gallatin County Search and Rescue and Highline Partners. This forecast does not apply to operating ski areas.

Mountain Weather

This morning the mountains near West Yellowstone and Cooke City have 4-6” of new snow with no new snow elsewhere. Temperatures are teens to low 20s F. Since yesterday morning wind has been strong to extreme out of the south-southwest with average speeds of 30-60 mph and gusts to 40-70 mph. Today, strong to extreme southwest winds will continue, and temperatures will be high 20s to low 30s F. Snow will continue near Cooke City and West Yellowstone where another 3-5” are possible, and elsewhere could get 1-3” by tomorrow morning.

Snowpack and Avalanche Discussion

The mountains near Cooke City received 2 feet of snow (equal to 2.3” snow water equivalent) since last Monday. Avalanches breaking below this snow are possible to trigger and could be large enough to bury a person, especially where recent snow has been drifted into slabs 1-3 feet thick. Strong wind will continue to grow these slabs today. Be extra cautious of steep, wind-loaded slopes. On Friday, skiers reported stability tests breaking below the recent snow (snowpit profile) which shows the potential to trigger slides. Avalanches breaking deeper than the recent snow are unlikely, but we have found weak layers deeper in the snowpack that are worth digging to look for and evaluate before riding steep slopes (video, video). Today, human triggered avalanches are possible and the avalanche danger is MODERATE.

Yesterday my partner and I skied at Mt. Blackmore in Hyalite and experienced constant 30-40+ mph winds (video) which occurred throughout the advisory area. In the mountains near Bozeman, Big Sky and West Yellowstone the strong south-southwest winds created fresh drifts of snow that a person could trigger today. These drifts might exist on any aspect, near ridgelines, across the middle of slopes, and locations where we don’t usually expect snow to be drifted into slabs. Look for cracking around your skis or sled as a sign the drifted snow is unstable. If you see these signs, stay off steep, wind-loaded slopes, especially where the consequences of getting caught in a slide involve being pushed over cliffs, or into rocks, trees, or gullies. Even without clear signs of instability, remain skeptical of wind-loaded slopes today (drifted Hyalite gullies video).

On slopes that do not have fresh drifts the snowpack is generally stable. There are weak layers that have formed, but they are not much of a concern until we receive more snow (Bridgers video).

Today the avalanche danger is MODERATE on wind-loaded slopes and LOW on all other slopes.

If you get out, please send us your observations no matter how brief. You can submit them via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).

Upcoming Education Opportunities:

Get your avalanche brain ready for the season at one of the many classes listed on our education calendar, and list of upcoming events below. Don’t delay preparing and inspecting your avalanche gear. Get some tips from Dave Zinn in this Pre-Season gear check video.

Wednesday, December 15, 6-7 p.m. FREE Sidecountry Avalanche Awareness for Families (and Friends). In partnership with Bozeman Parks and Recreation at Beall Park.  A 1-hr avalanche awareness talk with an emphasis on “Sidecountry Terrain and Snowpack.”

Friends of GNFAC Powder Blast Fundraiser

The Friends of the Avalanche Center are hosting the Virtual Powder Blast fundraiser. With only $3,500 left to go, help us reach the $65,000 goal. Your donations support free and low-cost avalanche education, beacon checkers at trailheads, beacon parks, weather stations, and GNFAC programs!

The Last Word

Sadly, yesterday a group of skiers were caught in an avalanche in the backcountry near Crystal Mtn., Washington and one person was killed. Link to Article. Our deepest condolences go out to those affected by this tragic event.


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