GNFAC Avalanche Forecast for Sat Dec 11, 2021

Not the Current Forecast

Good Morning. This is Ian Hoyer with the Gallatin National Forest Avalanche Forecast on Saturday, December 11th at 7:00 a.m. This information is sponsored by Alpine Orthopedics & Sports Medicine, Stronghold Fabrication and Knoff Group Real Estate. This forecast does not apply to operating ski areas.

Mountain Weather

Three inches of low density snow fell yesterday in the Bridger Range, 1” in Hyalite and the Madison Range, and a trace in the Lionhead area and around Cooke CIty. West and southwest winds have been blowing 20-30 mph with gusts of 45-60 mph. These strong west and southwest winds will continue today. Temperatures this morning are in the single digits and teens F. High temperatures will be in the teens and low 20s F. Snow showers will start this morning and pick up overnight, favoring the southern portion of the advisory area. By tomorrow morning, expect 4-6” around West Yellowstone and Cooke City with only a trace to 1” around Bozeman and Big Sky. Snowfall will continue tomorrow.

Snowpack and Avalanche Discussion

Avalanches breaking 1-3 ft deep beneath this week’s new snow are the primary concern today, particularly where strong winds have blown loose surface snow into new and deeper drifts. Strong southwest winds today will actively be forming new drifts. Skiers south of town yesterday got unstable test results on the new snow - old snow interface, showing that the potential for triggering slides exists. There are also weak layers lower in the snowpack that are worth looking for and evaluating before riding steep slopes (video, video). 

Human triggered avalanches are possible and the avalanche danger is MODERATE today.


Avalanches breaking in wind drifts are also the number one concern near Bozeman, Big Sky, and West Yellowstone. Yesterday, Alex found thin fresh wind drifts in the Bridger Range that were very easily triggered (video). While the drifts he found were thin and harmless, deeper drifts pose a very real hazard. Even in places without new snow, increasingly strong winds have formed fresh drifts. The strong winds mean these drifts may have formed in atypical locations, mid-slope or further below ridgelines than usual. Be on the look out for pillows of drifted snow. If there are any signs these drifts are reactive, steer clear of them on steep slopes. Even if they’re not giving you any warning signs, keep up a healthy skepticism (drifted Hyalite gullies video).

On non-windloaded slopes, conditions are mostly stable. There are weak layers that we’ll be monitoring, but they are not currently a major concern (Bridgers video).

The avalanche danger today 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 (, 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

Thank you to everyone who has submitted observations already this season! As we build our mental picture of the snowpack, your observations are even more helpful than usual. Please drop us a quick line and let us know what you’re seeing when you’re out and about in the mountains.

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