19-20

<p>In the mountains near Cooke City human triggered and natural avalanches were reported each of the last four weekends (<strong><a href="https://www.mtavalanche.com/node/21147">Dec 7</a></strong>, <strong><a href="https://www.mtavalanche.com/node/21201">Dec 13</a></strong>, <strong><a href="https://www.mtavalanche.com/node/21218">Dec 14</a></strong>, <strong><a href="https://www.mtavalanche.com/node/21222">Dec 14</a></strong>, <strong><a href="https://www.mtavalanche.com/images/19/large-natural-avalanche-near-cook… 22</a>,</strong> <strong><a href="https://www.mtavalanche.com/node/21368">Dec 27</a></strong>). These avalanches broke deep and wide on buried weak layers. They show a poor snowpack structure exists, and large, deadly avalanches are possible to trigger. See <strong><a href="https://www.mtavalanche.com/forecast/cooke-city">recent photos and videos on the regional page</a></strong> to see what is possible if you hit the wrong spot on a steep slope.</p>

<p>For the last couple weeks snowfall and wind have added minimal load to the snowpack. This allowed the snowpack to gain stability which means there are no warning signs like natural avalanches or collapsing. Multiple riders can make tracks on a slope before someone hits a weaker spot and triggers a large avalanche. Do not let tracks fool you into thinking a slope is safe. Carefully evaluate the snowpack and consequences of a slide before riding on steep slopes. Avalanche danger is MODERATE.</p>

<p>Near Big Sky and West Yellowstone the snowpack is supported by layers of sugary, weak snow that make large avalanches possible to trigger (<strong><a href="https://www.youtube.com/watch?v=Fd3eKZDCkB4&amp;list=PLXu5151nmAvSbcbVf…;, <strong><a href="https://www.mtavalanche.com/sites/default/files/2019-12/P1000212.JPG">p…;). The snowpack has adjusted to the weight of previous snowfall, but a weak layer could collapse and release an avalanche across an entire slope if a person hits the wrong spot (<u><strong><a href="https://www.youtube.com/watch?v=kuqUUzl0Wj8&amp;list=PLXu5151nmAvSbcbVf…;). Either avoid avalanche terrain, or carefully evaluate the snowpack and terrain before riding steep slopes. Your homework is to review media on our regional pages to see what the unstable snowpack looks like and where you are most likely to find it (<strong><a href="https://www.mtavalanche.com/forecast/lionhead">Lionhead page</a></strong>, <strong><a href="https://www.mtavalanche.com/forecast/northern-madison">N. Madison page</a></strong>). Today buried weak layers make avalanches possible to trigger and avalanche danger is MODERATE.</p>

<p>In the mountains near Bozeman potential avalanches are confined to fresh drifts of snow. Otherwise the snowpack is generally stable and deeper avalanches are not likely. Light to moderate winds formed fresh drifts with yesterday’s low density snow. These drifts are probably shallow and present minimal hazard, but should be carefully evaluated. Look for cracking under your skis as a sign fresh drifts are unstable. Avoid slopes where fresh drifts appear large or where slides could push you into hazards like trees or cliffs. Avalanche danger is LOW.</p>

<p>Triggering large avalanches is possible in the mountains near Big Sky and West Yellowstone. The widespread weak snow near the ground is still working to accommodate the load of new snow that fell earlier this week (<strong><a href="https://www.youtube.com/watch?v=kuqUUzl0Wj8&amp;list=PLXu5151nmAvSbcbVf…;). Have you noticed that we sound like a broken record? Every day: “weak snow at the ground … don’t trust it”. Well, get used to it. These weak layers don’t heal quickly. That’s why they are called <em>persistent</em> weak layers. We’ll be worried about these layers for weeks, if not months, to come. Each day without a new load avalanches become less likely, but this is a slow process and can’t be rushed. Avoiding riding on or beneath steep slopes is a simple way to stay safe while we wait. If you do get onto a steeper slope today, ride one at a time and have your partners watch from a safe spot, so they’re ready if something goes wrong. Human triggered avalanches are possible and the avalanche danger is MODERATE.</p>

<p>Yesterday, a rider saw two fresh large avalanches on a NE aspect of Henderson Mountain with snowmobile tracks nearby (<strong><a href="https://www.mtavalanche.com/node/21368">details and photos</a></strong>). It’s unclear if these broke naturally or were triggered by the snowmobilers. Either way, these slides are a cause for concern. They broke several hundred feet wide and up to four feet deep. That is a lot of snow moving downhill and not something you want to mess around with. Triggering a similar slide is possible today on weak layers buried in the middle of the snowpack. Think carefully about the consequences of triggering an avalanche and make a solid plan before getting into steep terrain. The avalanche danger is MODERATE.</p>

<p>The lower snowpack is generally stable. Thin wind slabs formed by moderate west winds yesterday are the primary concern but won’t be much of an issue outside of the steepest high consequence terrain. Look out for these wind drifts near the ridgeline and avoid them if you’re in a place where a small slide would be a big deal. Today, large avalanches are unlikely and the avalanche danger is LOW.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<strong><a href="https://www.mtavalanche.com/node/add/snow_observation">observation form</a></strong>, email us (<strong><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></strong&gt;), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>