Good morning. This is Alex Marienthal with the Gallatin National Forest Avalanche Forecast on Christmas Eve, Sunday, December 24th at 6:30 a.m. This information is sponsored by Spark R&D and Avalanche Alliance. This forecast does not apply to operating ski areas.
Yesterday the Bridger Range got 6” of new snow and 2-4” fell elsewhere. West-northwest wind averaged 15-25 mph with gusts of 35-45 mph yesterday, and this morning wind has tapered to 5-15 mph. Temperatures are single digits to teens F. Today temperatures will reach high teens F and wind will be westerly at 5-10 mph. The next chance for a little snow is Tuesday.
Yesterday’s 6-8” of new snow (0.6-0.8” snow water equivalent) fell on a weak and unstable snowpack which makes human-triggered avalanches likely. Weak layers of sugary facets are buried 1-2 feet deep and struggle to support the overlying snow. The additional weight of a person could cause the snow to collapse and avalanche on slopes steeper than 30 degrees. Yesterday Doug and I rode in Island Park where we saw a poor snow structure that showed unstable, propagating results in our snowpack tests (video, observation). Additionally, the new snow alone could avalanche, especially where it was drifted into thicker slabs by yesterday’s northwest-west wind and where it fell on weak, feathery surface hoar (photo). Be extra cautious of steep slopes today. Carefully assess the snowpack and practice cautious route finding. Human-triggered avalanches are likely and avalanche danger is CONSIDERABLE in the Bridger Range, south of Big Sky, and near West Yellowstone and Island Park.
Yesterday’s 2-5” of new snow (0.2-0.5” snow water equivalent) does not increase the avalanche danger, but heightened avalanche conditions persist due to a poor snowpack structure. Weak layers buried 1-2 feet deep have produced numerous avalanches and signs of instability over the last few weeks (avalanche log), and remain capable of causing large, dangerous avalanches. Yesterday a skier near Cooke City reported widespread collapses and “whumphs” (on each of the last two days), and one somewhat recent natural avalanche (photo and observation), clear signs a person can trigger an avalanche on buried persistent weak layers. Before traveling in avalanche terrain, carefully assess the snowpack for instability with a quick snowpit, adjust your plans if you see obvious signs of instability like collapsing or recent avalanches, and consider the consequences of being caught in an avalanche. Today, human-triggered avalanches are possible and avalanche danger is MODERATE near Big Sky, Hyalite and Cooke City.
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 (mtavalanche@gmail.com), 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.
Every weekend in Cooke City: Friday at The Antlers at 7pm, Free Avalanche Awareness and Current Conditions talk, and Saturday from 10am-2pm at Round Lake Warming Hut, Free Rescue Practice.
We offer Avalanche Fundamentals with Field Session courses targeted towards non-motorized travelers in January and one geared towards motorized users. Sign up early before they fill up.
Loss in the Outdoors is a support group for those affected by loss and grief related to outdoor pursuits. Check out the link for more information.
Feathery crystals of surface hoar blanket our advisory area. Bruce Jamieson and Simon Horton made a 3-part video series on how it forms and why it’s a problem.