18-19

<p>Weak facets make up the foundation of the snowpack in the Lionhead near West Yellowstone (<u><strong><a href="https://www.youtube.com/watch?v=kqiXL3X2coU&amp;t=0s&amp;list=PLXu5151n…;). This weak layer exists on all aspects and elevations. Without a wind load, the overlaying slab isn’t quite cohesive enough to propagate a fracture. On slopes that have wind drifted snow, the necessary ingredients exist to produce avalanches (<u><strong><a href="https://www.mtavalanche.com/images/18/poor-snowpack-structure-lionhead-…;).</p>

<p>Slopes leeward to west-southwest winds are the most likely to harbor thick slabs of wind drifted snow. Watch for signs of instability such as cracking/collapsing and avoid all steep slopes that appear to be wind loaded. If a slide does occur, it will fail at the ground and take season’s snowpack with it. This is not a scenario that ensures a positive outcome.</p>

<p>Today, wind loaded slopes hold the necessary ingredients to produce avalanches&nbsp;which have a&nbsp;<strong>MODERATE</strong> avalanche danger. Non-wind loaded slopes have a <strong>LOW</strong> avalanche danger.</p>

<p>The message is simple in the mountains around Bozeman, Big Sky and Cooke City: Avoid wind loaded slopes and avoid avalanches. Strong winds the past few days have hammered slopes on all aspects and elevations (<u><strong><a href="https://www.youtube.com/watch?v=jNaGEKhXO0I&amp;list=PLXu5151nmAvRNl9ku…;, <u><strong><a href="https://www.youtube.com/watch?v=eIscuLfDH8c&amp;list=PLXu5151nmAvRNl9ku…; <u><strong><a href="https://www.mtavalanche.com/images/18/reactive-wind-slabs-hyalite-12-de…; <u><strong><a href="https://www.mtavalanche.com/images/18/wind-slab-avalanche-blackmore1">p…;). Yesterday, my partner and I toured around the Throne in the northern Bridgers and found nearly every slope to be touched by the wind. Some slopes were scoured and firm while others had thick pillows of wind drifted snow. These thick drifts were stubborn and hard to move. The Big Sky and Bridger Bowl Ski Patrols also found fresh winds slabs reluctant to move during control work. Although wind loaded slopes are becoming harder to trigger, they still hold the potential to fail under the weight of a skier or rider. Fortunately, wind slabs are unlikely to propagate long distances and should stay relatively small in size. The lower portion of the snowpack remains strong and stable. &nbsp;&nbsp;&nbsp;&nbsp;</p>

<p>A secondary problem is a layer of small grained facets buried roughly a foot deep. This layer formed during the dry spell after Thanksgiving. We found this layer on the Throne and got it to propagate in one out of three stability tests (<strong><a href="https://www.youtube.com/watch?v=MAWIffJc_nA&amp;list=PLXu5151nmAvRNl9ku…;). Without a recent load this layer won’t be much of a problem, but will be something to track with the arrival of more snow, whenever that might be. &nbsp;</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> avalanche danger.</p>

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

<p>Over the past 48 hours the mountains near West Yellowstone picked up 4-6” of new snow totaling .3-.4” of SWE (<u><a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a></u>). This load was deposited on a snowpack with a very weak foundation. On Tuesday, I rode in the Lionhead area and found roughly two feet of snow on the ground with the bottom half consisting of sugary facets (<u><strong><a href="https://www.youtube.com/watch?v=kqiXL3X2coU&amp;t=0s&amp;list=PLXu5151n…;). These facets propagated easily in stability tests on any slope that had a cohesive slab of wind drifted snow (<u><strong><a href="https://www.mtavalanche.com/images/18/poor-snowpack-structure-lionhead-…;).</p>

<p>Today, dangerous avalanche conditions exist on wind loaded slopes. Terrain loaded by west-southwest winds will be especially vulnerable to unstable conditions. Given the poor snowpack structure, slopes without wind drifted snow also hold the potential to produce avalanches. Terrain management will be the key to safe travel today. Watch for and avoid all wind loaded slopes and keep slope angles less than 30 degrees.&nbsp;&nbsp; &nbsp;</p>

<p>Fresh snow, wind and a poor snowpack structure make human triggered avalanches likely on wind loaded slopes which have a <strong>CONSIDERABLE</strong> avalanche danger. Non-wind loaded slopes have a <strong>MODERATE</strong> avalanche danger.</p>

<p>Wind loaded slopes are main avalanche concern in the mountains around Bozeman, Big Sky and Cooke City. Moderate to strong winds out of the west-southwest in combination with fresh snow has created the perfect recipe for wind slab development. &nbsp;Yesterday, skiers up Divide Peak in the northern Gallatin Range observed active transport and signs of instability in wind loaded terrain (<u><strong><a href="https://www.youtube.com/watch?v=jNaGEKhXO0I&amp;list=PLXu5151nmAvRNl9ku…;, <u><strong><a href="https://www.mtavalanche.com/images/18/reactive-wind-slabs-hyalite-12-de…;). This is consistent with Doug’s observations from Mt. Blackmore on Tuesday (<u><strong>video</strong></u>, <u><strong><a href="https://www.mtavalanche.com/images/18/wind-slab-avalanche-blackmore1">p…;)</p>

<p>Today, strong winds are forecasted to continue, which will increase the size and distribution of fresh wind slabs. Watch for signs of instability such as shooting cracks and avoid all steeps slopes with rounded pillows of wind drifted snow. Fortunately, the lower portion of the snowpack is stable, which will keep avalanches confined to the new and wind-blown snow. With that said, it only takes a small slide to create a dangerous situation. Be especially cautious when traveling in terrain where trees, rocks, or gullies could amplify the consequences of being caught (<u><strong><a href="https://www.mtavalanche.com/node/19250">report</a></strong></u&gt;). &nbsp;</p>

<p>Today, human triggered avalanches are likely on wind loaded slopes which have a <strong>CONSIDERABLE</strong> avalanche danger. Non-wind loaded slopes have a <strong>MODERATE</strong> avalanche danger.</p>