Good morning. This is Alex Marienthal with the Gallatin National Forest Avalanche Forecast on Sunday, December 10th at 7:15 a.m. This information is sponsored by the Bozeman Ice Festival, Upper Yellowstone Snowmobile Club and Bridger Bowl. This forecast does not apply to operating ski areas.
Bridger Bowl has the lower mountain open this weekend. Uphill travel is permitted from a backcountry gate at the top of the Sunnyside Quad. Backcountry conditions exist above the Quad with no avalanche mitigation or ski patrol services. Call 911 for rescue.
This morning there is 1” of new snow in Cooke City, West Yellowstone and Island Park, and no new snow elsewhere. Wind has been out of the west-southwest at 15-30 mph with gusts of 30-55 mph. Temperatures are single digits to low 20s F this morning. Today, temperatures will reach teens to mid-20s F, and wind will remain moderate to strong out of the west at 15-35 mph. The southern half of our forecast area could get 2-4” of new snow with 1-3” elsewhere by tomorrow morning, and more snow tomorrow.
Yesterday was the third day in a row with reports of avalanches and widespread collapsing of the snowpack. A skier triggered and was not caught in a slide at Bridger Bowl in terrain that is currently the backcountry (photo), natural avalanches were reported in Beehive Basin (photos), Taylor Fork (photos) and Cooke City (photo), and skiers near West Yellowstone (photos) and Cooke City (observation) and climbers in Hyalite experienced large collapses (observation).
Across our forecast area the snowpack is unstable, and a person can easily trigger a dangerous avalanche. Slopes that had snow on the ground prior to last week’s new snow are the most dangerous, especially where recent strong winds also drifted snow into thicker slabs over the old snow. Snow that survived on the ground during November became faceted, sugary and weak and is struggling to support the weight of recent snow. We show this in our field videos over the last week from Bridger, Hyalite, Island Park, Cooke City and Lionhead (videos). Many recent observations also show signs of instability and support the need to travel cautiously in the mountains.
Now is not the time to travel on slopes steeper than 30 degrees. Avalanches that break on the old snow can be triggered from low angle terrain that is connected to steep slopes, so also consider terrain that is above and adjacent to you. With the recent gusty winds (photo), all wind-loaded slopes are suspect today. Be especially cautious of steep slopes that have fresh drifts, and any slope where there is old snow below last week’s snow.
Throughout our forecast area, human triggered avalanches are likely and the avalanche danger is CONSIDERABLE.
If you venture out, please fill an observation form. It does not need to be technical. Did you see any avalanches? How much snow is on the ground? Was the wind moving snow? Simple observations are incredibly valuable. You can also contact us via email (firstname.lastname@example.org), phone (406-587-6984), or Instagram (#gnfacobs).
Upcoming Avalanche Education and Events
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
Tuesday, December 12th, 9:00 a.m. to 3:00 p.m., West Yellowstone Motorized Avalanche Fundamentals, Pre-registration and more information HERE.
Thursday, December 14th, 6:30 p.m., Community Partnership Series @ MAP Brewing, featuring “RUN” with Wiley Miller, and Q&A with GNFAC forecaster Alex Marienthal
We offer Avalanche Fundamentals with Field Session courses targeted towards non-motorized users in December and January and one geared towards motorized users in January. Sign up early before they fill up.
Loss in the Outdoors, is a support group for those who have been affected by grief and loss related to outdoor pursuits. Check out the link for more information.
Listen to GNFAC Forecaster Dave Zinn on the Hoary Marmot Podcast for some extracurricular avalanche talk (link to episode).