18-19

<p>Over the last 24 hours more than a foot of heavy snow (1.2” of <u><a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a></u>) fell near West Yellowstone and the southern Madison and Gallatin Ranges, and snow continues this morning. Moderate southwest winds drifted this snow into thick slabs on an unstable snowpack. Ian skied at Bacon Rind in the southern Madison Range yesterday and found a layer of weak surface hoar below 6” of new snow. He got unstable test results on this weak layer and on a layer of sugary snow buried 2-3’ deep (<strong><a href="https://www.youtube.com/watch?v=8U0I_ZNd8pU&amp;t=0s&amp;index=2&amp;li…;). An additional 10-12” of snow since yesterday makes large natural and human triggered avalanches likely to break on these weak layers (<u><strong><a href="https://www.mtavalanche.com/images/19/large-avalanche-near-lionhead">ph…;, <u><strong><a href="https://www.mtavalanche.com/images/19/avalanches-breaking-weak-snowpack…;). Very dangerous avalanche conditions exist and avalanche danger is HIGH. Avoid travel on and underneath steep slopes.</p>

<p>Since yesterday the mountains near Cooke City and Big Sky have 8-10” of snow equal to 0.8 to 1.0” of SWE. These areas are a long distance apart, but today have similar avalanche conditions and travel advice. Moderate to strong southwest wind formed 1-2’ thick drifts that are easy to trigger. Natural avalanches are possible today where southwest wind continues to form heavy, thick drifts. On non-wind loaded slopes, avalanches of new snow and loose snow avalanches are easy to trigger. Avalanches could break 2-3’ deep and propagate wide on layers of weak, sugary facets. I was in Cooke City four days ago and had a large collapse (<u><strong><a href="https://www.youtube.com/watch?v=6nk39vqLWlQ&amp;list=PLXu5151nmAvRNl9ku…;, <u><strong><a href="https://www.youtube.com/watch?v=eINpY6r-ISA&amp;list=PLXu5151nmAvRNl9ku…;) where the snowpack was less than 3-4 feet deep. Carefully assess the snowpack and effects of the wind today. Avoiding avalanche terrain is advised while the snowpack adjusts to the weight of new snow. Avalanche danger is CONSIDERABLE.</p>

<p>Yesterday the Bridger Range and Hyalite got 3-5” of snow equal to 0.3-0.5” of SWE. This is not a lot of weight added to buried weak layers, but enough to keep them on edge. It is possible to trigger avalanches on 2-3’ deep on sugary facets where the snowpack is shallow (less than 3-4’). Last week’s observations from Mt. Ellis (<u><strong><a href="https://www.youtube.com/watch?v=Z0dOv0z4GDI&amp;t=0s&amp;list=PLXu5151n…;, <u><a href="https://www.mtavalanche.com/node/19903">avalanche incident</a></u></strong>) and large avalanches on <a href="https://www.mtavalanche.com/images/19/big-natural-avalanches-bridgers-3… Peak</a> and the <a href="https://www.mtavalanche.com/node/19808">West side of the Bridgers</a> show where this weak snowpack exists. Yesterday I went to the northern Bridger Range and found small fresh drifts of snow were easy to trigger (<strong><a href="https://www.youtube.com/watch?v=xO15cidZK20&amp;t=0s&amp;index=4&amp;li…;). These drifts are possible to trigger today, and could be hazardous in high consequence terrain. Today, buried weak layers and wind drifted snow make avalanches possible and avalanche danger is MODERATE.</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>Snowfall since yesterday afternoon favored the mountains from Big Sky to West Yellowstone with 3-6” of snow equal to 0.3-0.6” <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> (SWE). Steady snow showers are expected today and southwest wind will create thick, fresh drifts of snow that can easily be triggered by a snowmobiler or skier. Sugary weak snow buried in the lower half of the snowpack will be pushed to break by the weight of new and wind-drifted snow through today (<strong><a href="https://www.youtube.com/watch?v=hh3eSrv6fYI">video</a></strong&gt;). Large human triggered avalanches are likely and natural avalanches possible. Large slides during the last storm in the Centennials and Lionhead area are similar to what is likely today (<strong><a href="https://www.mtavalanche.com/images/19/large-avalanche-near-lionhead">ph…;, <strong><a href="https://www.mtavalanche.com/images/19/avalanches-breaking-weak-snowpack…;). Avoid travel on and below steep slopes, and plan for stability to decrease through the day. Avalanche danger is CONSIDERABLE.</p>

<p>Since yesterday the mountains near Cooke City received 5” of snow equal to 0.5” of SWE. The snowpack is shallow and weak on some slopes and deep and strong on other slopes (<u><strong><a href="https://www.youtube.com/watch?v=eINpY6r-ISA&amp;list=PLXu5151nmAvRNl9ku…;). This variability makes widespread large avalanches less likely. However, new snow today will test weak snow and make&nbsp;dangerous avalanches possible in specific areas where the snowpack is less than 4' deep. I was there a couple days ago and observed only one small avalanche from the last storm, but experienced one large, rumbling collapse on a slope with less than 3 feet of snow (<u><strong><a href="https://www.youtube.com/watch?v=6nk39vqLWlQ&amp;list=PLXu5151nmAvRNl9ku…;. </strong>Fresh drifts of snow 1-2’ thick will be easy to trigger, and they will grow in size with more snowfall and wind loading today. Avalanches could break deeper where the snowpack is shallow and weak. Avalanche danger is CONSIDERABLE on wind loaded slopes and MODERATE on non-wind loaded slopes.</p>

<p>The Bridger Range and Hyalite do not have any new snow this morning. It is possible to trigger avalanches 2-3’ deep on weak layers buried in the middle of the snowpack, similar to what we saw on Mt. Ellis last week (<strong><a href="https://www.youtube.com/watch?v=Z0dOv0z4GDI&amp;t=0s&amp;list=PLXu5151n…;, <a href="https://www.mtavalanche.com/node/19903">avalanche incident</a></strong>). New snow and wind through today will form fresh drifts that can avalanche under the weight of a person, and could break on deeper weak layers. Plan for stability to decrease through the day. Buried weak layers with expected new and drifted snow through today make avalanches possible to trigger. Avalanche danger is MODERATE.</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>