GNFAC Avalanche Forecast for Tue Dec 15, 2020

Not the Current Forecast

Good Morning. This is Dave Zinn with the Gallatin National Forest Avalanche Forecast on Tuesday, December 15th at 7:15 a.m. This forecast is sponsored by Gallatin County Search and Rescue and the Community Food Co-op. This forecast does not apply to operating ski areas.

*Note: Bridger Bowl Ski Area will open Thursday, December 17th. Bridger will be closed to uphill travel starting Wednesday at 1 a.m. and will remain closed to uphill travel 24/7 until the end of the season. There is no avalanche control or ski patrol services today. Backcountry conditions exist. Workers are setting up for the season and making snow. Please stay clear of work areas, snow guns, chairlifts, and other equipment.

Mountain Weather

The mountains around Big Sky and West Yellowstone received 2-3” of new snow in the last 24 hours while the Bridger Range and the mountains around Cooke City remained dry. Winds are 5 to 15 MPH from the southwest to northwest and temperatures are in the high single digits to mid-teens F. Temperatures will rise to the high teens to low 20s F with 10 to 15 MPH winds from the southwest today that will increase this evening. The mountains around West Yellowstone will have 2-4” by morning with the rest of the advisory area receiving a trace to 2”.

Snowpack and Avalanche Discussion

Snow tapered off yesterday in the mountains around Bozeman, Big Sky, and West Yellowstone with snow totals ranging from 5 to 8” equal to 0.3-0.4” snow water equivalent (SWE) since Friday. Yesterday, moderate west winds in the Bridger Range created small drifts near ridgelines (photo). Light winds in the rest of our area did not move much snow. These ranges have a weak foundation that will avalanche when loaded with a slab of new or wind drifted snow, but we are not there yet (Beehive video, Hyalite video, Saddle Peak video, Buck Ridge video, Lionhead video).

Instabilities today will be limited to loose snow avalanches in steep, rocky terrain like those I observed in Hyalite (photo) and Beehive (photo) in the last two days and isolated drifts of snow. These small avalanches could have outsized consequences if they push a skier or rider into obstacles such as trees or off cliffs. They are occasionally entraining the weak, faceted snow near the ground and gaining volume (photo).

Be obsessed about the consequences of small avalanches and carefully assess the snowpack looking for isolated instabilities before entering avalanche terrain. Today, avalanches are unlikely and the danger is LOW.

The snowpack around Cooke City is stronger and deeper than the rest of our advisory area and it is supporting the 4” of new snow (0.3” SWE) from this weekend. While the snowpack is generally strong, skiers and riders have found slopes with weak layers of surface hoar and sugary facets (video, photo). Dig down to assess the snowpack to look for these instabilities. Learn how and what to look for in Doug and Bruce Jamieson’s recent ECT video. Instability today is limited to isolated drifts of snow and small, loose snow avalanches in steep, technical terrain that can knock a rider or skier off their sled or feet.

Carefully assess the snowpack and consequences of a small slide before entering avalanche terrain. Today the avalanche danger is LOW.

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

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