Snowpack and Avalanche Discussion
<p>The Avalanche Warning expires this morning for the mountains near West Yellowstone and the southern Madison and Gallatin Ranges, but dangerous avalanche conditions exist. Since Saturday, these mountains got 11-18” of snow equal to .7-1” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> (SWE). Strong wind drifted this snow into thick slabs on top of a fragile snowpack. Light to moderate wind will continue to load slopes today. On Friday, we toured near Hebgen Lake and found two feet of unsupportive, sugary snow on the ground (<u><strong><a href="https://www.youtube.com/watch?v=MeTYd9mOyGk&list=PLXu5151nmAvRNl9ku…;, <u><strong><a href="https://www.mtavalanche.com/images/18/shallow-weak-unstable-hebgen">pho…;). Riders near Lionhead found similar conditions (<strong><a href="https://www.mtavalanche.com/node/19430">details</a></strong>). Today, natural and human triggered avalanches are likely on wind loaded slopes and human triggered avalanches are likely on all steep slopes. Avoid riding on and below steep slopes. Avalanches can be triggered from flat terrain below and small slopes can be as deadly as large slopes. Avalanche danger is <strong>HIGH</strong> on wind loaded slopes and <strong>CONSIDERABLE</strong> on non-wind loaded slopes.</p>
<p>Yesterday, the mountains near Big Sky and Hyalite got 9-12” of new snow equal to .8” of snow water equivalent (<a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2…;), and the Bridger Range got 9” of snow equal to 1” of SWE. The prior two days, these mountains got 8-12” of low density snow. Yesterday, skiers found unstable slabs of new snow in the Bridger Range (<strong><a href="https://www.mtavalanche.com/node/19466">details</a></strong>) and Hyalite (<strong><a href="https://www.mtavalanche.com/node/19464">details</a></strong>, <strong><a href="https://www.mtavalanche.com/node/19459">details</a></strong>). Strong wind out of the southwest yesterday and north-northwest overnight formed fresh drifts that are easy to trigger on most aspects. On non-wind loaded slopes, dry loose avalanches and storm slabs can be triggered. Avalanches breaking deeper than the new snow are less likely, but a layer of facets buried 1.5 to 2’ deep is still propagating in stability tests. Yesterday, Doug and I got unstable test results on this layer on Buck Ridge (<strong><a href="https://www.youtube.com/watch?v=V_SxEcDhZME&list=PLXu5151nmAvRNl9ku…;, <strong><a href="https://www.mtavalanche.com/images/18/buck-ridge-instability-0">photo</…;) and snow bikers had similar observations in the northern Gallatin Range (<strong><a href="https://www.mtavalanche.com/images/18/ectp-28-n-gallatin">photo</a></st…;). Avalanche danger is <strong>CONSIDERABLE</strong> on wind loaded slopes and <strong>MODERATE</strong> on non-wind loaded slopes. Be cautious of fresh drifts and avoid steep slopes if you see collapsing or cracking of the snow surface.</p>
<p>The mountains near Cooke City got 8-10” of snow since Friday. Yesterday, skiers triggered a small drift of new snow (<strong><a href="https://www.mtavalanche.com/images/18/small-instabilities-near-cooke-ci…;). Today, these fresh drifts are possible to trigger. Drifts are smaller and more isolated than in the rest of the advisory area, and a lack of wind today allows them to stabilize. A layer of facets 1-1.5’ below the surface is capable of producing avalanches. Doug found this layer last week (<u><strong><a href="https://www.youtube.com/watch?v=W6iS9ManzPo&index=2&list=PLXu51…;, <u><strong><a href="https://www.mtavalanche.com/images/18/instability-near-lulu-pass">photo…;), and on Friday a snowmobiler triggered an avalanche that broke on this layer (<a href="https://www.mtavalanche.com/images/18/snowmobiler-triggered-mt-abundanc…;). On slopes with less than three feet of snow, the snowpack is weak and sugary to the ground (<u><strong><a href="https://www.youtube.com/watch?v=4Vb2Y4UZJ1Q&index=2&t=0s&li…;). Today, new snow and buried weak layers make avalanches possible to trigger and avalanche danger is <strong>MODERATE</strong>.</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>, email (<u><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></u>), phone (406-587-6984), or Instagram (#gnfacobs).</p>
