18-19

<p>With a widespread poor snow structure, it remains possible to trigger a large avalanche. The base of the snowpack consists of 1.5’ of weak snow, capped by a 1-3’ thick slab of more cohesive snow (<strong><a href="https://www.mtavalanche.com/images/19/buried-weak-layers-cabin-creek">p…;). The southern mountains received a foot of heavy snow followed by strong winds at the beginning of last week. As we get further out from that loading event, signs of instability are becoming less frequent, but have not gone away. Yesterday, we got a report of a natural avalanche near Reynolds Pass, just outside of our advisory area (<a href="https://www.mtavalanche.com/images/19/reynolds-pass-avalanche">photo</a…;). On Sunday, skiers in the southern Madison Range skiers got significant collapsing on a similar snowpack and saw a recent avalanche (<strong><a href="https://www.mtavalanche.com/node/19699">details and photo</a></strong>).</p>

<p>The large natural and human triggered avalanches that broke during and immediately after last week’s storm provide good examples of the sort of slides you could trigger today (<strong><a href="https://www.youtube.com/watch?v=b3LBdamYYvU&amp;t=0s&amp;list=PLXu5151n…;, <strong><a href="https://www.mtavalanche.com/node/19639">details</a></strong&gt;, <strong><a href="https://www.mtavalanche.com/node/19672">details</a></strong&gt;). Each day without snowfall, the snowpack is slowly becoming more stable, but this is a slow process. Triggering an avalanche remains possible, and the avalanche danger is MODERATE. Snow flurries this afternoon won’t impact the avalanche danger.</p>

<p>It’s been two weeks since the last significant snowfall in the northern ranges (<strong><a href="https://www.mtavalanche.com/images/19/snowpack-graph-snotel-gnfac-area-… of January’s snowfall</a>)</strong>. Without a new load, stability has slowly improved and triggering an avalanche has become unlikely. This doesn’t mean that you couldn’t find a pocket of unstable snow out there somewhere, just that those areas are becoming fewer and farther between. The structure to look out for is a cohesive slab (1-2’ thick) over weak layers that formed in early December. Alex and I found this structure on Sunday near Buck Ridge (<strong><a href="https://www.youtube.com/watch?v=VnA2ZhT8vzY&amp;list=PLXu5151nmAvRNl9ku…;) </strong>and Eric found it on Saturday just north of Big Sky (<strong><a href="https://www.youtube.com/watch?v=Ryd8fZKwVmo&amp;list=PLXu5151nmAvRNl9ku…;

<p>While it’s becoming unlikely you’ll find them, still be on the hunt for signs of instability (cracking, collapsing, recent avalanches, unstable test results) and be ready to change your plans accordingly if you do. Digging down to look for weak snow and testing the interface between these layers is always a good idea. The avalanche danger is LOW.</p>

<p>If you get out and have any avalanche or snowpack observations to share, contact us 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>The mountains near West Yellowstone and the southern Madison and Gallatin ranges have a poor snowpack structure that makes it possible to trigger large, dangerous avalanches. There is 1.5’ of sugary, unsupportive facets on the ground below a 1-3’ thick slab (<u><strong><a href="https://www.mtavalanche.com/images/19/buried-weak-layers-cabin-creek">p…;). Last Thursday we found this unstable snowpack in Cabin Creek (<u><strong><a href="https://www.youtube.com/watch?v=BQ6V8-Pdb3M&amp;t=0s&amp;list=PLXu5151n…;). Yesterday in the southern Madison Range skiers got significant collapsing on a similar snowpack and saw a recent avalanche (<strong><a href="https://www.mtavalanche.com/node/19699">details and photo</a></strong>).</p>

<p>A week ago these mountains received a foot of heavy snow followed by strong wind. During and after this storm large natural and human triggered avalanches broke 2-3’ deep (<u><strong><a href="https://www.youtube.com/watch?v=b3LBdamYYvU&amp;t=0s&amp;list=PLXu5151n…;, <u><strong><a href="https://www.mtavalanche.com/node/19639">details</a></strong></u&gt;, <u><strong><a href="https://www.mtavalanche.com/node/19672">details</a></strong></u&gt;). Similar slides are possible to trigger today. No snow or wind loading since the middle of last week means the snowpack is becoming more stable, but collapsing yesterday is a clear sign that avalanches are possible to trigger.&nbsp;Today, avalanche danger is MODERATE.</p>

<p>In the mountains near Bozeman, Big Sky and Cooke City weak layers are buried shallower and are less widespread than in the southern ranges and near West Yellowstone, but an unstable snowpack exists on some slopes. Before riding on steep slopes, dig to determine the snowpack structure and avoid slopes with the recipe for an avalanche: 1-2’ feet of wind drifted snow on top of weak, sugary facets. This list of recent observations indicates, at a minimum, where this unstable structure exists:</p>

<ul>
<li>On Friday, on the south face of Mt. Abundance near Cooke City a snowmobiler triggered an avalanche 1-2' deep and large enough to bury a person&nbsp;(<u><strong><a href="https://www.mtavalanche.com/node/19684">details</a></strong></u&gt;, <u><strong><a href="https://www.mtavalanche.com/images/19/snowmobile-triggered-mt-abundance…;).</li>
<li>On Saturday north of Big Sky Eric found this unstable recipe for an avalanche and had one low angle slope collapse (<u><strong><a href="https://www.youtube.com/watch?v=Ryd8fZKwVmo&amp;list=PLXu5151nmAvRNl9ku…;
<li>Yesterday south of Big Sky, Ian and I found a similar snowpack structure that produced unstable test results, and we saw a recent snowmobile triggered avalanche (<strong><a href="https://www.mtavalanche.com/images/19/snowmobile-triggered-avalanche-mc…;, <strong><a href="https://www.youtube.com/watch?v=VnA2ZhT8vzY&amp;list=PLXu5151nmAvRNl9ku…;
<li>Yesterday on the west side of the Bridger Range&nbsp;skiers got multiple collapses, and in their stability tests the column of snow collapsed when they isolated it (<strong><a href="https://www.mtavalanche.com/node/19703">details</a></strong&gt;).</li>
</ul>

<p>The northern mountains have received only 2-4” of snow in 2019 (<strong><a href="https://www.mtavalanche.com/images/19/snowpack-graph-snotel-gnfac-area-… days</a></strong>). Despite this lack of heavy loading, recent signs of instability and human triggered avalanches indicate an unstable snowpack and avalanches are possible to trigger. Above freezing temperatures today also add the possibility for wet loose avalanches and cornice falls (<a href="https://www.mtavalanche.com/node/19702"><strong>details</strong></a&gt;). Today, 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&gt;, email (<u><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></u&gt;), phone (406-587-6984), or Instagram (#gnfacobs).</p>