The wind picked up in the Bridger Range and transported snow into unstable drifts. Photo: GNFAC
23-24
We triggered a small avalanche on a test slope at the ridgeline of the ramp. Wind was transporting the recent snow into drifts sensitive to human triggers. Photo: GNFAC
Forecast link: GNFAC Avalanche Forecast for Mon Dec 25, 2023GNFAC Avalanche Forecast for Tue Dec 26, 2023
Collapsing on Barronette
From YouTube comment 12/22/23: "I am an alpine climber - descended from Barronnette today, went south all the way down the ridgeline and descended the gully above the start of the XC trail. Heard 10+ instances of whomping and slope collapsing under my feet on both avalanche and non-avalanche slopes on N & E aspects."
Collapsing on Barronette
From YouTube comment 12/22/23: "I am an alpine climber - descended from Barronnette today, went south all the way down the ridgeline and descended the gully above the start of the XC trail. Heard 10+ instances of whomping and slope collapsing under my feet on both avalanche and non-avalanche slopes on N & E aspects."
GNFAC Avalanche Forecast for Sun Dec 24, 2023
<p><span><span><span><span><span><span>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 (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=I2EByh1Yqa4&list=PLXu5151nmAvSH326z…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/29656"><span><span><span><strong><span…;). 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 (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/23/big-surface-hoar"><span><span><sp…;). 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.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>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 (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/avalanche-activity"><span><span><span><stro… log</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>), 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 (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/29657"><span><span><span><strong><span… and observation</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>), 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.</span></span></span></span></span></span></p>
Upcoming Avalanche Education and Events
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
We snowmobiled up to 9,000' on Sawtelle peak, then skied to dig a couple pits. Our first pit was on an East aspect on a heavily wind loaded slope. The HS was 130cm (or 4.2 feet). There was 8" of new snow equal to 0.85" SWE, sitting over old consolidated snow that made up a slab over soft, weak facets about 50cm off the ground. We had ECTP24 x2 break on the old weak snow.... Photo: GNFAC
Forecast link: GNFAC Avalanche Forecast for Sun Dec 24, 2023
We snowmobiled up to 9,000' on Sawtelle peak on 12/23/23. The snow depth at 8,800' was 3-4 feet. Photo: GNFAC
Widespread collapsing north of Cooke
From email 12/23: "Widespread collapsing yesterday. Approx 20 significant collapses. Many shaking trees 50'+ away."
Widespread collapsing near Cooke
From email 12/23: "Continued, widespread collapsing today. About 10 good ones, and that was with very minimal trailbreaking/ about 700' vert."