17-18

<p>Over the past three days the mountains around Cooke City have received nearly three feet of snow totaling 2.5” of SWE. This rapid and heavy load has put a tremendous amount of stress on the snowpack, which is creating very dangerous avalanche conditions. Yesterday, a person&nbsp;was partially buried up Sheep Creek outside of Cooke City. The slide broke 2’ deep, 200’ wide and occurred on a south-southwest facing slope. Details are vague, but it sounds like he was uninjured. This slide is consistent with other observations from the area. Natural avalanches were also observed yesterday on mid-elevation, south-facing slopes (<a href="https://www.mtavalanche.com/images/17/large-natural-avalanche-cooke-cit…;, <a href="https://www.mtavalanche.com/images/17/sign-instability-woody-ridge"><st…;, <a href="https://www.mtavalanche.com/images/17/natural-avalanche-town-hill-cooke…;).</p>

<p>Slides appear to be failing on a layer of facets buried 2-3’ deep, which are sitting on top of the Thanksgiving ice crust. This problem does not exist on all slopes, and seems to be mostly confined to slopes with a southerly aspect. As new and wind-blown snow add stress to this layer, it will continue to be problematic.</p>

<p>Slopes do not need to harbor a buried persistent weak layer in order to produce avalanches. With continued snow and wind today, natural and human triggered avalanches will be likely on all wind loaded slopes which have a <strong>HIGH</strong> avalanche danger. Non-wind loaded slops have a <strong>CONSIDERABLE </strong>avalanche danger.</p>

<p>The snowpack in the Lionhead area near West Yellowstone has a weak structure. Facets buried 2-3’ feet exist on all aspects and elevations. This persistent weak layer has been pushed to its breaking point by recent snow and wind. Yesterday, Doug and his partner observed numerous avalanches while riding around the area (<strong><a href="https://www.youtube.com/watch?v=85UQeqSWXqk&amp;list=PLXu5151nmAvQSYtIf…;, <strong><a href="https://www.mtavalanche.com/images/17/lionhead-crown">photo</a></strong…;). Under these conditions, avalanches have the ability to be triggered remotely. This means you can trigger an entire slope from flat or low angle terrain. Today, careful snowpack evaluation and terrain management will be essential.</p>

<p>As the snowpack continues to be stressed by new and wind-blown snow, human triggered avalanches will be likely on all slopes and the avalanche danger is rated <strong>CONSIDERABLE</strong>. If the storm hits harder than expected today, the avalanche danger could rise to <strong>HIGH</strong> on all slopes.</p>

<p>A mostly stable snowpack in the mountains around Bozeman and Big Sky has kept avalanche activity to a minimum. Yesterday, I toured on the west side of the Bridgers and was pleasantly surprised by the overall stability. Facets near the Thanksgiving ice crust weren’t breaking in stability tests and we did not observe any recent avalanche activity&nbsp;(<strong><a href="https://www.youtube.com/watch?v=z-C1MLt6WDQ">video</a></strong&gt;). These observations are consistent with other reports from the area.</p>

<p>As the next storm settles in, new snow instabilities will be the main concern. Wind slabs and storm slabs will grow in size and distribution as the storm progresses. Watch for cracking/collapsing in the new snow and avoid steeper slopes where signs of instability are present.</p>

<p>Today, snow and wind will make human triggered avalanches likely on wind loaded slopes which have <strong>CONSIDERABLE</strong> avalanche danger. Non-wind loaded slopes have <strong>MODERATE</strong> avalanche danger.&nbsp;</p>

<p>If you get out and have any avalanche or snowpack observations to share, drop a line via our <a href="https://www.mtavalanche.com/node/add/snow_observation">website</a&gt;, email (<a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a&gt;), phone (406-587-6984), or Instagram (#gnfacobs).</p>