17-18

<p>New snow and wind loading are the main concern across the advisory area. Over the past three days, most mountain locations have picked up a foot or more of snow totaling 1-1.3” of snow water equivalent (<a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2…;) (<a href="https://www.youtube.com/watch?v=3os-hIuvWyc&amp;t=0s&amp;index=1&amp;li…;, <strong><a href="https://www.youtube.com/watch?v=0j-w-w85tDM">video</a></strong&gt;). This new snow has been deposited on variety of old snow surfaces. On some slopes the new snow rests over a melt freeze crust, while on others it sits over a thin layer of facts that formed during the short dry spell earlier in the week (<a href="https://www.youtube.com/watch?v=zw4alNn9YUE&amp;t=0s&amp;list=PLXu5151n…;). Either way, steep slopes will be touchy to human triggers today, primarily those that have been wind loaded. Winds are forecasted to remain moderate to strong throughout the day, which will increase the size and distribution of wind slabs. Pay attention to blowing and drifting snow and avoid being on or underneath slopes that appear to be heavily wind loaded (<a href="https://www.mtavalanche.com/images/18/large-human-triggered-slide-cabin…;).</p>

<p>On non-wind loaded slopes, soft slabs and dry loose avalanches (sluffs) are also possible (<a href="https://www.mtavalanche.com/images/18/dry-loose-avalanches-hyalite"><st…;). In the mountains near West Yellowstone, there’s a slight chance for slides to fail on a layer of surface hoar buried 2-3’ deep. Yesterday, I rode in Cabin Creek in the southern Madison Range and found this layer in both my snowpits. Fortunately, it did not propagate in stability tests, which is a good indication it’s getting stronger. However, it’s still possible to trigger a slide on this layer in isolated areas.</p>

<p>Today, the combination of new snow and wind 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>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>It seems that there’s always something happening in Cooke City, usually involving heavy snow, heavy wind or both. Yesterday, Doug rode north of town and found a foot of fresh snow sitting over a thin layer of facets (<strong><a href="https://www.youtube.com/watch?v=zw4alNn9YUE&amp;t=0s&amp;list=PLXu5151n…;). This layer formed during the three-day dry spell earlier in the week. This weak layer will be most reactive on wind loaded slopes. Watch for cracking and collapsing within the new snow, these are warning signs that unstable conditions exist. Be extra conservative on all steep slopes today (<strong><a href="https://www.mtavalanche.com/images/18/natural-avalanches-ynp">photo</a>…;), especially those with wind drifted snow, and always be thinking about the consequences of a slide.</p>

<p>Today, fresh snow available transport combined with moderate to strong winds out of the west will make human triggered avalanches likely on wind loaded slopes, which have a <strong>CONSIDERABLE</strong> avalanche danger. On non-wind loaded slopes, human triggered avalanches are possible and the avalanche danger is rated <strong>MODERATE</strong>.</p>

<p>By yesterday afternoon, 6-10” of new snow accumulated in the mountains around Bozeman and Big Sky. The snow that fell was low density and easily transported by moderate winds out of the west. Yesterday, Alex and his partners found 10” of fresh snow on Divide Peak in Hyalite. The new snow was unreactive in stability tests on non-wind loaded slopes, but wind slabs near the ridgelines were a concern (<strong><a href="https://www.youtube.com/watch?v=3os-hIuvWyc&amp;t=0s&amp;index=1&amp;li…;). Today, moderate to strong westerly winds will continue to load slopes in upper elevation leeward terrain. Fresh wind slabs near ridgelines and cross loaded sub-ridges will be sensitive to human triggers today. Dry loose avalanches (sluffs) will also be possible in steeper terrain today (<strong><a href="https://www.mtavalanche.com/images/18/dry-loose-avalanches-hyalite">pho…;).</p>

<p>Outside of new snow instabilities, the snowpack is generally stable (<a href="https://youtu.be/GOpY8hRn4iM"><strong>video</strong></a&gt;).</p>

<p>Today, sensitive wind drifts 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>The main concern in the southern mountains is wind loaded slopes. Fresh snow combined with 20-30 mph westerly winds will form fresh drifts in upper elevation, leeward terrain. On Wednesday, a snowbiker up Cabin Creek triggered a large and dangerous slide on a heavily wind loaded slope (<strong><a href="https://www.mtavalanche.com/images/18/large-human-triggered-slide-cabin…;). Fortunately, nobody was injured in this event. Today, I would steer clear of wind loaded slopes, specifically those in steeper terrain.</p>

<p>A secondary problem is a layer of buried surface hoar. This layer is gaining strength and does not have a widespread distribution, but still holds the potential to produce avalanches (<a href="https://www.mtavalanche.com/images/18/surface-hoar-stripe-pit"><strong>…;, <a href="https://youtu.be/vC1Z1rae2uE"><strong>video</strong></a&gt;). Keep an eye out for this layer if you’re traveling on steep, sheltered slopes.</p>

<p>Continued snow and wind today will make human triggered avalanches likely on wind loaded slopes which have a <strong>CONSIDERABLE </strong>avalanche danger. Non-wind loaded slopes have <strong>MODERATE</strong> avalanche danger.</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>