19-20

<p>Doug and I spent the last two days north of Cooke City looking at several large, human triggered avalanches from earlier in the weekend (<a href="https://www.youtube.com/watch?v=INHkAhf3L5o&amp;list=PLXu5151nmAvSbcbVf…;, <a href="https://www.mtavalanche.com/photos?field_advisory_year_target_id=438&am…;, <a href="https://www.mtavalanche.com/avalanche-activity"><strong>activity log</strong></a><strong>)</strong>. These avalanches broke 3-6’ deep and 100-250’ wide. Riders likely triggered these avalanches when they hit thin areas in the snowpack and their weight impacted the weak snow. Today, it is possible to trigger similar avalanches on slopes where heavy wind slabs cap a weak layer facets near the ground. While the story is challenging because some slopes are unstable and others are not, the solution is simple. Avoid steep slopes with heavy slabs of snow and you will avoid the primary hazard (<a href="https://www.youtube.com/watch?v=FAgWx6yXR2U"><strong>video</strong></a&…;). Carefully assess the snowpack if you choose to ride in steep terrain. The avalanche danger is rated MODERATE and it is possible to trigger large avalanches.</p>

<p>The mountains from Big Sky to West Yellowstone have weak facets near the ground. While obvious signs of instability such as cracking and “whumphing” of the snowpack are unlikely, human triggered avalanches breaking two to three feet deep and spreading wide across steep slopes are still possible. A stability test will likely be your first clue that something is amiss (<a href="https://www.youtube.com/watch?v=Fd3eKZDCkB4&amp;list=PLXu5151nmAvSbcbVf…;, <a href="https://www.mtavalanche.com/sites/default/files/styles/very_large_1200w…;, <a href="https://www.mtavalanche.com/images/19/natural-avalanche-near-lionhead">…;). As snow starts falling later this afternoon, expect the avalanche danger to increase. Human triggered and natural avalanches occurred on many steep slopes during the last snowstorm (<a href="https://www.mtavalanche.com/images/19/natural-avalanche-near-lionhead">… 1</strong></a><strong>, </strong><a href="https://www.mtavalanche.com/images/19/2nd-yellowmule-avalanche"><strong…;, </strong><a href="https://www.mtavalanche.com/node/21249"><strong>3</strong></a&gt;). End 2019 safely by avoiding avalanche terrain or carefully assessing the snowpack and the consequences of an avalanche. Large, human triggered avalanches are possible and avalanche danger is MODERATE.</p>

<p>Yesterday, mid-elevation winds in the Bridger Range formed fresh, unstable drifts of snow. During avalanche mitigation work, the Bridger Bowl Ski Patrol triggered 12-18” deep hard slab avalanches in isolated areas lower on slopes where this wind created new instabilities. Last night, ridge winds picked up and formed similarly unstable drifts. Look for these drifts high on slopes as well as lower elevations in more uncommon areas. Aside from areas of windblown snow, generally stable conditions will continue until the Bridger and Northern Gallatin Ranges start getting new snow later this afternoon (<a href="https://www.youtube.com/watch?v=I-VZBhHGN_k&amp;list=PLXu5151nmAvSbcbVf…;). Avalanche Danger is MODERATE on wind-loaded slopes and LOW everywhere else. Avoid areas where small avalanches could have oversized consequences.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<a href="https://www.mtavalanche.com/node/add/snow_observation"><strong>observat… form</strong></a>, email us (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

<p>Over the last month, several large natural and human triggered avalanches occurred near Cooke City (<strong><a href="https://www.mtavalanche.com/photos?field_advisory_year_target_id=438&am…;, <strong><a href="https://www.mtavalanche.com/avalanche-activity">activity log</a></strong>). These avalanches broke deep and wide on heavily wind loaded slopes that have weak snow at the base of the snowpack. Yesterday Dave and Doug investigated a few snowmobile triggered slides that happened Friday. Their <strong><a href="https://www.youtube.com/watch?v=INHkAhf3L5o&amp;list=PLXu5151nmAvSbcbVf…; and <strong><a href="https://www.mtavalanche.com/images/19/1-snowmobiler-triggered-avalanche…; show the type of steep, heavily wind loaded terrain to avoid in order to avoid invovelment with a similar deadly avalanche. Carefully evaluate the terrain and snowpack before riding on steep slopes. Today large avalanches are possible to trigger and avalanche danger is MODERATE.</p>

<p>Near Big Sky and West Yellowstone buried weak layers had time to adjust to the weight of previous storms. This has helped the snowpack gain stability, but the poor snowpack structure needs more time (<u><strong><a href="https://www.youtube.com/watch?v=Fd3eKZDCkB4&amp;list=PLXu5151nmAvSbcbVf…;). Avalanches are more difficult to trigger, but can break 2-3 feet deep on weak sugary snow near the ground (<strong><a href="https://www.mtavalanche.com/sites/default/files/styles/very_large_1200w…;, <strong><a href="https://www.mtavalanche.com/images/19/natural-avalanche-near-lionhead">…;). Warning signs like natural avalanches and collapsing are unlikely. Avoid avalanche terrain, or carefully evaluate the snowpack and terrain before riding steep slopes. Large human triggered avalanches are possible and avalanche danger is MODERATE.</p>

<p>In the Bridger Range, moderate mid-mountain wind created fresh drifts from the recent low density snow. These drifts are small, but can be triggered in less common locations at lower, mid-mountain elevations. Otherwise, in the mountains near Bozeman the snowpack is generally stable and instabilities are confined to the recent few inches of very low density snow. I skied near Fairy Lake yesterday and saw a thin, stable snowpack and small natural dry loose avalanches (<strong><a href="https://www.youtube.com/watch?v=I-VZBhHGN_k&amp;list=PLXu5151nmAvSbcbVf…;). Today be on the lookout for fresh drifts and dry loose avalanches. Avoid terrain where the consequences of a slide increase due to hazards like cliffs or trees, like a lot of the terrain on Saddle Peak. Small avalanches can be triggered today, otherwise larger avalanches are unlikely and avalanche danger is LOW.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<u><strong><a href="https://www.mtavalanche.com/node/add/snow_observation">observation form</a></strong></u>, email us (<u><strong><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></strong></u&gt;), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>