24-25

<p>Since Friday, the mountains near Cooke City, West Yellowstone, and Island Park have received 16-30” of snow, equivalent to 2-3” of snow water equivalent, with Cooke City coming out on top. Snow fell on weak surfaces and strong winds are drifting new snow into cohesive slabs, making human-triggered avalanches likely on many slopes.</p>

<p><strong>Persistent slab avalanches</strong> breaking 1-3 feet deep on buried weak layers of facets and surface hoar formed during last week’s high pressure are likely. These will break widely and may be triggered remotely from terrain near steep slopes. Avalanches failing on older weak layers buried near the base of the snowpack are possible. The likelihood of avalanches is amplified on wind-loaded slopes where the weight of drifted snow adds stress to weak layers.</p>

<p>Take the relatively short list on the <a href="https://www.mtavalanche.com/avalanche-activity"><span>Avalanche Activity Log</span></a> with a grain of salt, given limited visibility:</p>

<ul>
<li>On Monday, Mark triggered a wind-loaded slope in the Centennial Mountains from a flat ridge top that broke 200 feet wide (<a href="https://youtube.com/shorts/26MdlE8SkEc"><strong><span>video</span></str…;)</li>
<li>A rider in the Lionhead area performed a re-entry, triggering a very small avalanche (<a href="https://youtube.com/shorts/I1BdaDmw-ko"><strong><span>video</span></str…;)</li>
<li>We received reports of a few small wind slab avalanches over the weekend near Cooke City (<a href="https://www.mtavalanche.com/avalanche-activity"><strong><span>avalanche log</span></strong></a>).</li>
</ul>

<p><span>Avoid wind-loaded slopes and limit travel on any slope steeper than 30 degrees. This requires cautious route-finding and conservative decision-making. The avalanche danger is CONSIDERABLE. <span>&nbsp;</span></span></p>

<p>The Madison and Gallatin Ranges received 12-20” of snow equal to 1.2-1.6” of SWE since Friday. The Big Sky area received the top end of this range.</p>

<p>Twenty to 40 mph winds are transporting recent snow into cohesive slabs and making human-triggered avalanches likely. Yesterday, <span>wind-loaded slopes cracked under our skis on switchbacks and in stability assessments in Beehive Basin (</span><a href="https://youtube.com/shorts/PBsMPg_BBQw"><strong><span>video</span></str…;), and </span>on Sunday, Mark and Alex observed cracks shooting 10-50 feet from their sleds in the Taylor Fork. Weak layers formed at the surface during last week’s high pressure are the primary culprit (<a href="https://www.mtavalanche.com/node/33944"><strong><span>observation</span…;, <a href="https://www.youtube.com/watch?v=y7Nm5dbbBqQ"><strong><span>video</span>…;

<p>Avoid wind-loaded slopes where human-triggered <strong>persistent slab </strong><span>and </span><strong>wind slab avalanches </strong>are likely. Dig down a few feet to look for weak layers and test for instability before considering travel on non-wind-loaded terrain steeper than 30 degrees. Shooting cracks, collapsing and recent avalanche activity supersede any indicator of <em>stability. </em></p>

<p>The avalanche danger level is CONSIDERABLE on wind-loaded slopes and MODERATE on other slopes in the Madison and Gallatin Ranges.</p>

<p>The Bridger Range has received less snow than the rest of the forecast area, with 11” equal to 1.0” of SWE since Friday and less wind. Avalanches are possible within recently drifted snow. With light winds, areas of concern for <strong>wind slab avalanches </strong>are upper-elevation terrain near ridgelines, on more prominent alpine faces and below cornices.</p>

<p>While weak layers formed under last week’s clear skies exist on some slopes, windy and warmer conditions interrupted widespread weak layer formation in the Bridger Range. Evaluate slopes for shooting cracks, a stiffening of the snow surface, and potential wind-loading before considering steep terrain. Dig below the recent snow to evaluate for instability at the interface of the older snow and snow that fell since Friday.</p>

<p><span>Human-triggered avalanches are possible, and the avalanche danger is MODERATE. </span></p>

<p><span><span><span><span><span><span>Since Friday, near Cooke City, West Yellowstone and Island Park got 14-24” of snow equal to 1.8-2.2” snow water equivalent (SWE) with 3.4” SWE at Black Bear SNOTEL near Island Park. Strong southwest winds have been drifting this snow into thicker slabs, and on many slopes the prior snow surface is a weak layer of sugary snow (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/33903"><span><span><span><strong><span…;). We received reports of a few small wind slab avalanches over the weekend near Cooke City, but visibility was very limited (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/avalanche-activity"><span><span><span><stro… log</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). </span></span></span></span></span></span></p>

<p><span><span><span><strong>Persistent slab avalanches</strong></span></span></span><span><span><span><span><span><span>&nbsp;will break wide on weak layers buried below the new snow, especially on wind-loaded slopes. There is a chance a slide could break 4-6 feet or deeper on weak layers at the bottom of the snowpack. Steady snowfall and strong wind will continue today making large to very large human-triggered and natural avalanches likely. Avoid travel on and underneath slopes steeper than 30 degrees. The avalanche danger is HIGH on all slopes.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Near Big Sky, Hyalite and Taylor Fork got 10-17” of snow equal to 1.0-1.3” of SWE since Friday. This snow was drifted into slabs that will be easy for a person to trigger today. Yesterday Mark and I rode into Taylor Fork and saw cracks shooting 10-50 feet out from our sleds, and all of our stability tests propagated with little force on weak layers below the new snow (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/33944"><span><span><span><strong><span… and observation</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>, </span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=y7Nm5dbbBqQ"><span><span><span><strong>…;

<p><span><span><span><span><span><span>On wind-loaded slopes human-triggered </span></span></span></span></span></span><span><span><span><strong><span><span>persistent slab avalanches</span></span></strong></span></span></span><span><span><span><span><span><span> are likely. These avalanches could break wide, be triggered from flatter terrain connected to steep slopes, and remain easy to trigger for multiple days. Where the snow is not drifted, avalanches are still possible. Avoid steep, wind-loaded slopes, and before travelling on any steep slope carefully assess the stability of the new snow. Danger is CONSIDERABLE on wind-loaded slopes and MODERATE on other slopes in the Madison and Gallatin Ranges.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>The Bridger Range got 8” of snow equal to 0.7” SWE since Friday and a few more inches will fall today. The new snow is being drifted into thicker slabs that make </span></span></span></span></span></span><span><span><span><strong><span><span>wind slab avalanches</span></span></strong></span></span></span><span><span><span><span><span><span> possible to trigger today.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>The Bridgers had more wind and warm temperatures compared to other parts of our area during the recent high pressure which interrupted weak layer formation. Weak layers still probably formed on some slopes, just not as widespread as the rest of the forecast area.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>If you plan to travel on slopes steeper than 30 degrees watch out for fresh drifts, and dig down below the new snow and drifts to assess for potential instability. If you see cracking across the snow surface, assume fresh drifts will slide on steeper slopes. Also stay alert for </span></span></span></span></span></span><span><span><span><strong><span><span>dry-loose avalanches</span></span></strong></span></span></span><span><span><span><span><span><span> on sustained steep slopes, especially where they could push you over a cliff or into rocks or trees. Human-triggered avalanches are possible and avalanche danger is MODERATE in the Bridger Range.</span></span></span></span></span></span></p>