17-18

<p>The Lionhead area near West Yellowstone has 4 feet of snow on the ground with 1.5 feet of new snow since Wednesday. This new snow rests over weak, sugary facets above a firm crust and creates dangerous avalanche conditions (<a href="https://www.youtube.com/watch?v=Kl0SZcPkP4I&amp;index=2&amp;list=PLXu51…;). Snowmobilers or skiers can easily collapse this unstable snowpack and trigger large avalanches. Be extra cautious if travelling on or below slopes steeper than 30 degrees. Avalanches are possible to trigger from flat terrain and low on slopes. Expose only one person at a time when riding or crossing below steep slopes.</p>

<p>Today, avalanches are easy to trigger on and below steep slopes and the avalanche danger is <strong>CONSIDERABLE</strong>.</p>

<p>Near Bozeman and Big Sky the mountains have 4-5 feet of snow on the ground, and near Cooke City there is 6-8 feet. New snow since Wednesday totaled 14-20” and was very low density. Yesterday, moderate to strong northwest wind drifted new snow into slabs near ridgelines (<strong><a href="https://www.mtavalanche.com/images/17/wind-transporting-snow-ridgetops"…;), and these slabs will continue to grow today. These wind slabs are 1-3 feet deep, easy to trigger, and could be wide and extend far downslope. Be cautious of wind loaded slopes and large cornices. Avoid steep slopes if you see cracking and collapsing of the snow, and minimize exposure to high consequence terrain like steep slopes above cliffs.</p>

<p>Secondary to wind slabs, there are some slopes where it is possible to trigger an avalanche on a layer of facets 2-3 feet deep. I rode around the mountains near Cooke City the last two days and searched for unstable snow without success (<a href="https://www.youtube.com/watch?v=i_IKXNUrU5g"><strong>video</strong></a&…;). Eric looked for this layer at Taylor Fork on Thursday, and also found stable snow in his snow pits (<a href="https://www.youtube.com/watch?v=u7_Z88o2aaQ&amp;list=PLXu5151nmAvQSYtIf…;). A few small avalanches have been observed on this layer of facets (<a href="https://www.mtavalanche.com/images/17/natural-avalanche-cooke-city-1"><…;, <strong><a href="https://www.mtavalanche.com/images/17/small-avalanche-facets-near-bacon…;) and it is weaker in some areas (W. side of Bridgers). It is worth digging 3 feet to test for this instability before riding steep terrain.</p>

<p>Today, wind slabs are easy to trigger and the avalanche danger is <strong>CONSIDERABLE</strong> on wind loaded slopes and <strong>MODERATE</strong> on non-wind loaded slopes. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</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>Although the Lionhead area received the least amount of snow out of this storm, it has the weakest snowpack and most dangerous avalanche conditions. A collapsible layer of facets sitting over the Thanksgiving Ice curst is the most problematic layer. This problem likely exists on all aspects and elevations. On Thursday, snowmobilers got this layer to propagate easily in stability tests and avoided all steep terrain (<a href="https://www.youtube.com/watch?v=Kl0SZcPkP4I&amp;index=2&amp;list=PLXu51…;

<p>Today, I would be extra cautious when traveling on or underneath any slopes steeper than 30 degrees. Avalanches have the potential to be triggered from a distance or low on the slope. It’s mandatory under these conditions that skies and riders only expose one person at a time in steeper terrain and always watch each other from a safe location.</p>

<p>Today, an unstable structure makes human triggered avalanches likely on all slopes and the avalanche danger is rated <strong>CONSIDERABLE</strong>.</p>

<p>This was a classic cold smoke storm that heavily favored the northern ranges and Cooke City. Big Sky topped the charts with 16-18” over&nbsp;the past day and half. The mountains around Cooke City received a similar amount while the Bridger Range squeezed out 12-14”. This sounds like a ton of snow, which it was, but it was very low density and did not add a significant amount of weight to the snowpack. Most areas only received .5 to .7” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2…;

<p>Today, the main avalanche concerns will be wind slabs and loose snow avalanches (sluffs). Wind slabs will be most prevalent in terrain leeward to west-northwest winds (<a href="https://www.mtavalanche.com/photos"><strong>photo</strong></a><strong&gt;, </strong><a href="https://www.mtavalanche.com/images/17/avalanche-wind-loaded-slope"><str…;). These slabs will be sensitive to human triggers and have the potential to entrain large volumes of snow once they get moving. Loose snow avalanches also have potential to pick up heavy amounts of snow once they get rolling in steep terrain.</p>

<p>A secondary concern is avalanches failing on a layer of facets buried a few feet deep. This layer hasn’t been highly reactive, but has produced signs of instability and few recent avalanches. Yesterday, Alex was in Cooke City and did not get this layer to propagate in stability tests (<strong><a href="https://www.youtube.com/watch?v=i_IKXNUrU5g">video</a></strong&gt;). However, a few recent avalanches have been observed around Cooke City that appear to have failed on this layer (<strong><a href="https://www.mtavalanche.com/images/17/natural-avalanche-cooke-city-1">p…;). This problem is tricky because the strength and distribution of this layer is highly variable. It’s worth digging down a few feet and doing a stability test before committing to steeper terrain (<a href="https://www.youtube.com/watch?v=u7_Z88o2aaQ&amp;list=PLXu5151nmAvQSYtIf…;

<p>Today, wind slabs will be easy to trigger and the avalanche danger is rated <strong>CONSIDERABLE</strong> on wind loaded slopes. Non-wind loaded slopes have a&nbsp;<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>