GNFAC Avalanche Forecast for Sat Dec 26, 2020

Not the Current Forecast

Good Morning. This is Alex Marienthal with the Gallatin National Forest Avalanche Forecast on Saturday, December 26th at 7:00 a.m. This forecast is sponsored by Gallatin County Search and Rescue and Highline Partners. This forecast does not apply to operating ski areas.

Mountain Weather

This morning there is no new snow, temperatures are high 20s to low 30s F and wind is west-southwest at 15-25 mph with gusts of 40-50 mph. Today, temperatures will cool to the 20s F and wind will remain westerly at 15-30 mph with gusts over 40 mph. Snow is expected this morning in the southern mountains and will move north through the day. By tomorrow morning the mountains near Bozeman and Big Sky will have 3-5” of new snow with 5-8” possible near West Yellowstone and Cooke City.

Snowpack and Avalanche Discussion

Yesterday a skier triggered a large avalanche on the Football Field path of Saddle Peak, immediately south of Bridger Bowl’s boundary. He was luckily not caught or injured. We are very thankful for his timely report to us and ski patrol to ensure everyone was ok (photos and details). The avalanche broke 1-2 feet deep on a layer of very weak, sugary facets on the ground. This layer is some of the weakest snow we have seen in years, and it exists in the Bridger Range, Hyalite, Big Sky, Taylor Fork and West Yellowstone (and everywhere in-between).

Recent activity is a sign that this weak snow at the ground is struggling to support additional weight. Yesterday in Hyalite a skier triggered a large collapse on a low angle slope (details). On Thursday I saw natural avalanche crowns on Bridger Peak (photo). Last weekend, Dave and I saw avalanches and weak facets in Taylor Fork (video), and he and Doug triggered a couple avalanches at Lionhead (details and video). Careful terrain selection is your best defense against this problem. Avoid slopes steeper than 30 degrees all together, or carefully assess the snowpack and minimize exposure to terrain traps to reduce the consequences of a slide.

Today it is possible to trigger avalanches breaking on sugary persistent weak layers 1-3 feet deep. Snow and wind will form fresh slabs that could make avalanches easier to trigger. Be extra cautious of wind loaded slopes, and anticipate stability to decrease where snowfall today is heavy. The avalanche danger is MODERATE.

In the mountains near Cooke City the snowpack is 4-6 feet deep with a stronger foundation than the rest of our advisory area. Our primary avalanche concern is the 2 feet of snow (2.2” snow water equivalent) that fell earlier in the week, and slopes where it is drifted into thick slabs.

During the storm on Tuesday and Wednesday there were natural avalanches and a skier triggered avalanche on steep, wind-loaded slopes (video, video, details). The last couple days skiers reported collapsing of the snowpack in low angle terrain which is a sign the recent snow can still avalanche on steep slopes. Today avalanches are possible to trigger and the avalanche danger is MODERATE. Avoid steep, wind-loaded slopes and carefully assess the stability of the recent snow before riding slopes steeper than 30 degrees.

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 Avalanche Education and Events

See our education calendar for an up to date list of all local classes. Here are a few select upcoming events and opportunities to check out:

Every Saturday in Cooke City, FREE snowpack update and rescue practice at the Round Lake Warming Hut between 10 a.m. and 3 p.m. Poster with More Info.

January 20 & 21 (plus field sessions the following weekends), Avalanche Fundamentals with Field Course. There are separate field sessions tailored for both skiers and splitboarders (Bridger Bowl) and snowmobilers (Buck Ridge). Register here.

The Last Word

There have been four avalanche fatalities in the mountains of CO and WY since last Friday. We are deeply saddened by these events. You can find reports of these slides here.

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