GNFAC Avalanche Forecast for Sat Dec 12, 2020

Not the Current Forecast

Good Morning. This is Ian Hoyer with the Gallatin National Forest Avalanche Forecast on Saturday, December 12th at 7:30 a.m. This information is sponsored by Summit Motorsports and Ski-Doo and Montana State Parks. This is our first daily avalanche forecast and danger ratings for the season. Alex will issue the next forecast by 7:30 tomorrow morning.

*Note: Bridger Bowl Ski Area is closed and there is no avalanche control or ski patrol services. Backcountry conditions exist. Workers are setting up for the season and making snow. Please stay clear of work areas, snow guns, chair lifts and other equipment.


Mountain Weather

Since yesterday morning, 2-4” of light snow fell across the advisory area (0.1-0.2” snow water equivalent). Winds are light out of the west. Temperatures are single digits to teens F. Snow flurries will taper off this morning. Winds today will remain light out of the west. High temperatures will be in the high teens to low 20s F. Skies will clear this afternoon. Another round of snowfall arrives tomorrow evening.

Snowpack and Avalanche Discussion

The snowpack around Bozeman, Big Sky, and West Yellowstone is shallow and weak. Total snow depths in the mountains generally range from 1-2 ft. Weeks of high pressure have gradually weakened this shallow snowpack (Lionhead video, Beehive video). Once a slab builds above this weak foundation, the snowpack will rapidly become unstable (Saddle Peak video, Buck Ridge video). Last night’s few inches of low density new snow with light winds didn’t build a significant slab on most slopes. However, keep your eyes open for isolated drifts of new snow deeper than 6-8”. If you find one of these drifts, evaluate the snowpack carefully or just steer clear.

With such a weak foundation, expect the avalanche danger to rise as snow totals creep up in the coming days. 

For today, avalanches are unlikely and the avalanche danger is LOW.

The snowpack around Cooke City is deeper and generally not as weak as in the rest of the advisory area. Total snow depths range from 2-4 ft. This deeper snowpack was able to handle the weeks of high pressure without weakening as much. However, we have found some pockets of weak, sugary snow lower in the snowpack and there have been a few reports of buried surface hoar, so we’re not totally in the clear going forward (video). As with the rest of the advisory area, yesterday’s new snow wasn’t enough to build much of a new slab. With a more solid foundation, the avalanche danger won’t spike as quickly as more new snow accumulates over the coming days. 

The avalanche danger is LOW today.

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. Starts this Saturday, November 28. Poster with More Info.

Wednesday, December 16, 6-7 p.m., FREE online 1-hr Avalanche Awareness sponsored by Uphill Pursuits.

Monday, December 21, 6-7 p.m., FREE online 1-hr Avalanche Awareness sponsored by Mystery Ranch. Join HERE.

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

Welcome to the start of the 2020/2021 daily avalanche advisory 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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