17-18

<p>The biggest concern in the mountains around Cooke City is wind loaded slopes. Winds have been relatively calm over the past 24 hours, but strong westerly winds caused significant loading earlier in the week. Wind loaded slopes in steep rocky terrain or below ridgelines will be the most prone to producing avalanches. Evaluate snow and terrain carefully and approach all steep, wind loaded slopes with caution.</p>

<p>Slides failing on a thin layer of facets 1.5-2’ deep are also possible. On Tuesday, this layer produced unstable results in stability tests on a south facing slope around 10,000 ft. (<a href="https://youtu.be/yu1AnPdOjaI"><strong>video</strong></a&gt;). Look for and asses this thin layer of facets before committing to steeper slopes.</p>

<p>For today, wind-loading and buried weak layers make human triggered avalanches possible and the avalanche danger is rate <strong>MODERATE</strong>.</p>

<p>Wind slabs are the main concern in the mountains around Bozeman, Big Sky and West Yellowstone (<a href="https://youtu.be/qrBwGzmoDdA"><strong>video</strong></a&gt;). Watch for rounded pillows of wind drifted snow below ridgelines, cliff bands or steep convex rolls (<a href="https://www.mtavalanche.com/images/18/natural-avalanche-airplane-bowl">…;). The best way to mitigate the wind slab hazard is to avoid all wind loaded slopes steeper than 30 degrees. In addition to wind loaded slopes, cornices are an ever growing problem (<a href="https://www.mtavalanche.com/images/18/cornices-north-bridger-bowl-bound…;). These bus sized chunks of snow can fail under the weight of a single person and can break farther back than you might expect. Give them a wide buffer along the ridgelines and limit exposure time on slopes below (<a href="https://www.mtavalanche.com/images/18/skier-triggered-cornice-hyalite">…;).</p>

<p>Today, human triggered avalanches are possible on wind-loaded slopes which have a <strong>MODERATE</strong> avalanche danger. Non-wind loaded slopes have a <strong>LOW</strong> danger since the snowpack is generally stable.</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>

<p>Moderate to strong westerly winds have readily transported low density snow into thick wind slabs. Wind loaded slopes are most widespread in upper elevation terrain where winds have been the strongest. Watch out for large cornices, wind rolls or any visual evidence the slope is heavily wind loaded. Approach these slopes with caution or avoid them all together. Wind loaded slopes will be the most likely to produce avalanches today.</p>

<p>Slides failing on a thin layer of facets 1.5-2’ deep are also possible. On Tuesday, I found this layer on a south facing, non-wind loaded slope around 10,000 ft. This layer produced unstable results in stability tests (<a href="https://youtu.be/yu1AnPdOjaI"><strong>video</strong></a&gt;). We did not find this layer to be reactive on north facing slopes, which indicates its distribution is sporadic. Look for and asses this thin layer of facets before committing to steeper terrain.</p>

<p>For today, wind-loading and&nbsp;buried weak layers make human triggered avalanches possible and the avalanche danger is rate <strong>MODERATE</strong>.</p>

<p>Dense wind slabs that formed over the past few days remain a concern. These thick, cohesive slabs rest over lower density snow, which is creating an unstable structure. On Tuesday, Doug found this to be the main avalanche problem in the Bridges (<a href="https://youtu.be/qrBwGzmoDdA"><strong>video</strong></a&gt;). The Big Sky Ski Patrol also found this problem across Lone Mountain yesterday as did skiers up Mt Blackmore (<strong><a href="https://www.mtavalanche.com/images/18/wind-slab-mt-blackmore">photo</a>…;). Winds have calmed slightly over the past 12 hours, which has given these slabs a little time to stabilize. Although wind load slopes won’t be quite a sensitive today, I would still treat them with respect, especially in steep high consequence terrain.</p>

<p>Large cornices are also a major concern (<a href="https://www.mtavalanche.com/images/18/cornices-north-bridger-bowl-bound…;). These have grown huge over the past few weeks and remain under a tremendous amount of stress. On Monday, skiers up Hyalite unintentionally triggered a large cornice as they traversed along the ridge (<a href="https://www.mtavalanche.com/images/18/skier-triggered-cornice-hyalite">…;). The cornice broke only a few feet from where they were standing and took out part of their skin track. This is a good reminder to give cornices a wide berth both on and below the ridgelines (<a href="https://www.mtavalanche.com/images/18/cornice-illustration"><strong>ill…;, <strong><a href="https://www.mtavalanche.com/images/18/natural-avalanche-airplane-bowl">…;).</p>

<p>Today, human triggered avalanches are possible on wind-loaded slopes which have a <strong>MODERATE</strong> avalanche danger. Non-wind loaded slopes have a <strong>LOW</strong> danger since the snowpack lacks widespread weak layers and is generally stable.</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>

<p>Eric is in Cooke City and found blowing snow, wind-loading and also a wafer-thin weak layer of small-grained facets 18” under the surface, which he describes in his (<strong><a href="https://youtu.be/yu1AnPdOjaI">video</a></strong&gt;). This is the same layer I saw a week ago, but it now has a thicker slab of snow sitting on it. This layer was unstable in his tests and found on many slopes, wind-loaded and not. The good news is that it may not be a problem for long, but in the meantime assume it’s on most slopes until proven otherwise. Thick drifts and a few avalanche crowns are reminders that wind-loaded slopes could still avalanche (<strong><a href="https://www.mtavalanche.com/images/18/natural-avalanche-mt-republic">ph…;). For today, wind-loading and a buried weak layer point to the possibility of avalanches and a <strong>MODERATE</strong> danger.</p>

<p>From the Bridger Range, to Big Sky and West Yellowstone, winds formed large cornices and also blew snow into thick slabs that could avalanche. On Monday, skiers up Hyalite near Maid of the Mist came close to falling off a cliff when a cornice broke inches away from their feet. It triggered the slope below which wiped out part of their track (<a href="https://www.mtavalanche.com/images/18/skier-triggered-cornice-hyalite">…;). Yesterday, my partner and I skied north of Bridger Bowl along the ridge, ever mindful of the Hyalite incident. I kept my path on solid ground near the trees as we passed huge cornices (<strong><a href="https://www.mtavalanche.com/images/18/big-cornices">photo</a></strong&gt;, <strong><a href="https://www.mtavalanche.com/images/18/cornices-north-bridger-bowl-bound…;) giving them a wide berth (<strong><a href="https://www.mtavalanche.com/images/18/cornice-illustration">illustratio…;).</p>

<p>Our snowpit revealed wind slabs no more than a foot thick overlying softer snow, an unstable structure that could produce avalanches, which I talk about in our <strong><a href="https://youtu.be/qrBwGzmoDdA">video</a></strong&gt;. Other relevant observations include a small avalanche in Middle Basin north of Big Sky (<strong><a href="https://www.mtavalanche.com/images/18/middle-basin-natural-avalanche">p…;), large cornices along Buck Ridge (<a href="https://www.mtavalanche.com/images/18/cornices-second-yellowmule"><stro…;), and an avalanche under a corniced ridge in Teepee Basin (<a href="https://www.mtavalanche.com/images/18/avalanche-wind-loaded-slope-tepee…;). Today’s concerns are limited to wind-loaded slopes which have a <strong>MODERATE</strong> avalanche danger. All other slopes have a <strong>LOW</strong> danger since the snowpack lacks widespread weak layers and has good stability.</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>