GNFAC Avalanche Forecast for Wed Dec 16, 2020

Not the Current Forecast

Good Morning. This is Dave Zinn with the Gallatin National Forest Avalanche Forecast on Wednesday, December 16th at 7:15 a.m. This forecast is sponsored by the Upper Yellowstone Snowmobile Club and Blitz Motorsports and Yamaha. This forecast does not apply to operating ski areas.

*Note: Bridger Bowl Ski Area will open tomorrow. Bridger is closed to uphill travel today and will remain closed to uphill travel 24/7. Workers are setting up for the season. Please stay clear of the ski area today.

Mountain Weather

The southern ranges picked up 4-6” of new snow in the last 24 hours with 1-3” in the north. Winds increased to 15-30 MPH with gusts into the 50s MPH from the west to southwest except in Cooke City where they were 5-10 MPH from the northwest. Today, strong winds will continue to blow from the west to southwest at 20-30 MPH with temperatures in the 20s F. An additional 4-6” of snow will fall in the southern ranges with 1-2” in the north by morning.

Snowpack and Avalanche Discussion

The southern ranges received 4-6” of new snow equaling 0.2-0.4” of snow water equivalent (SWE) and strong winds are actively blowing and drifting the fresh snow onto a weak foundation of sugary facets as Doug observed at Lionhead yesterday (video). Snowfall and wind drifting will continue today, heightening the avalanche conditions on all slopes and creating dangerous avalanche conditions on slopes with fresh drifts where human triggered avalanches will be likely. Avoid steep wind-loaded slopes and look for obvious signs of instability such as recent avalanche activity, “whumphing,” and shooting cracks from your sled or skis before entering any avalanche terrain.

The avalanche danger is rated CONSIDERABLE wind-loaded slopes and MODERATE on all other slopes.

The northern ranges received 1-3” of new snow (0.1-0.2” SWE) with strong west to southwest winds. The snowpack structure is weak and human triggered avalanches are possible on slopes where the wind deposited drifts are loading the shaky foundation. Yesterday, north of Bridger Bowl, Ian and I noted that a slab was the missing ingredient before we see avalanches, our current weather will complete the recipe (Ramp video). This same story applies to all the ranges around Bozeman and Big Sky (Beehive video, Hyalite video, Saddle Peak video, Buck Ridge video). On non-wind-loaded slopes, the new snow’s weight is not enough to increase the avalanche danger and human triggered avalanches will be limited to isolated areas in steep, rocky terrain. Watch for signs of instability and dig a quick snowpit before entering any avalanche terrain (video).

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

Lacking the widespread weak layers found in the rest of our advisory area, the snowpack in Cooke City will support yesterday’s 3” of new snow (0.2” SWE). Avalanches will be small and confined to the recent snow in steep and extreme terrain. These slides can have outsized consequences if they push a rider or skier into terrain traps such as rocks, trees, and cliffs. Assess the snowpack before entering avalanche terrain and use safe travel practices by only exposing one person at a time and carrying all avalanche rescue equipment.

Today the avalanche danger is LOW in the mountains around Cooke City.

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.

TONIGHT, 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

Doug worked with Bruce Jamieson on a video about when, where and how to perform stability tests. Watch it here.