Snowpack and Avalanche Discussion
<p>In the mountains south of Big Sky to West Yellowstone the snowpack is poorly supported by 1.5’ of weak, sugary facets on the ground (<u><strong><a href="https://www.mtavalanche.com/images/19/poor-structure-s-madison-range">p…;, <u><strong><a href="https://www.youtube.com/watch?v=l0aklSLqYaM&list=PLXu5151nmAvRNl9ku…;, <u><strong><a href="https://www.youtube.com/watch?v=zj26vpS2WE0">video</a></strong></u>). Yesterday, Eric rode into Tepee Basin and found a recent snowmobile triggered avalanche. The slide was triggered near the bottom of the slope and broke a foot deep on rotten, sugary snow at the base of the snowpack (<strong><a href="https://www.youtube.com/watch?v=fXzzClQFS5s&t=0s&list=PLXu5151n…;, <strong><a href="https://www.mtavalanche.com/images/19/recent-avalanche-tepee-basin-5-ja…;). Yesterday in the Centennial Range a similar avalanche was triggered (<strong><a href="https://www.mtavalanche.com/images/19/snowmobile-triggered-avalanche-ne…;).</p>
<p>More snow and strong wind today will add weight and stress this weak snowpack. Avalanches will be easy to trigger and natural avalanches are possible. Avalanches can be triggered from low angle terrain below steep slopes, and as <a href="https://www.youtube.com/watch?v=fXzzClQFS5s&t=0s&list=PLXu5151n… describes in his video</a> even a small slide can have fatal consequences. Avalanche danger is <strong>CONSIDERABLE</strong> and could rise to <strong>HIGH</strong> with more snow and wind today. Be conservative and avoid avalanche terrain today.</p>
<p>In the mountains near Bozeman and Big Sky, weak, sugary snow that formed in December is buried 1-2’ deep and creates a poor snowpack structure. We received reports of large collapses most days the past week (<strong><a href="https://www.mtavalanche.com/weather/wx-avalanche-log">Activity log</a></strong>, <strong><a href="https://www.mtavalanche.com/images/19/collapse-and-crack-road-cut">phot…;), and yesterday in Middle Basin a skier triggered an avalanche that broke on hollow, sugary snow 1-2’ deep (<strong><a href="https://www.mtavalanche.com/images/19/skier-triggered-avalanche-middle-…;, <strong><a href="https://www.mtavalanche.com/node/19567">details</a></strong>). This recent activity shows avalanches breaking on this buried persistent weak layer are possible to trigger without the addition of stress from new snow. Be extra conservative with terrain selection and carefully evaluate the snowpack before travel on steep slopes. Avalanche danger is <strong>MODERATE</strong> today and could rise to <strong>CONSIDERABLE</strong> with snow and wind this afternoon.</p>
<p>The mountains near Cooke City have a highly variable snowpack. Some slopes are strong, others are weak without an unstable slab on top, and some slopes are unstable. Doug’s videos from last week show examples of weak and unstable slopes (<u><strong><a href="https://www.youtube.com/watch?v=W6iS9ManzPo&t=0s&list=PLXu5151n…;, <u><strong><a href="https://www.youtube.com/watch?v=4Vb2Y4UZJ1Q&t=0s&list=PLXu5151n…;). No snow since last weekend and minimal wind gave buried weak layers time to adjust. Strong wind last night drifted snow into fresh slabs that might rest over buried weak layers. Today, fresh drifts are possible to trigger and more likely to break where they formed over weak snow. On non-wind loaded slopes, avalanches breaking on these weak layers are unlikely. Today, avalanche danger is <strong>MODERATE</strong> on wind loaded slopes and <strong>LOW</strong> elsewhere.</p>
Upcoming Avalanche Education and Events
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
BOZEMAN
January 8, Women’s Specific Avalanche Awareness, 6:30-8 p.m. Story Mill Park, Bozeman.
January 9, 1-hr Avalanche Awareness, 7-8 p.m. Spire Climbing Center, Bozeman.
