20-21

<p>Last night, a storm in the Bridger Range dropped 8” of new snow equal to 0.8” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a>-SWE and 1-3” in the Northern Gallatin and the Northern Madison Ranges equal to 0.2-0.3” SWE. Winds blowing 25-35 mph from the west to southwest and gusting to 75 mph are drifting recent snow into heavy slabs on slopes at many elevations that will sensitive to human-triggers. When I went to look at a 10’ deep snowmobile-triggered avalanche in McAtee Basin on Sunday, the wind had deposited a 1-2’ deep slab of drifted-snow on the bed-surface in less than 24-hours (<a href="https://mtavalanche.com/images/21/large-avalanche-mcatee-basin"><strong…;, <a href="https://www.youtube.com/watch?v=65JO-4w4qXo"><strong>video</strong></a&…;). While snow fell last night, as far as the snowpack is concerned the loading has been going on for days. Recent avalanches are evidence of the danger. These include several very large, natural avalanches in the Northern Gallatin Range, natural avalanches in the Bridger and Northern Madison Range that failed near the ground, several snowmobile-triggered slides near Buck Ridge, and a fatal avalanche in Beehive Basin just over a week ago. See the <a href="https://mtavalanche.com/photos"><strong>photos page</strong></a> and the <a href="https://mtavalanche.com/avalanche-activity"><strong>avalanche activity page</strong></a> on our website for images and more information about these events.</p>

<p>Avalanches within the new and freshly drifted snow are likely today, more destructive, deep-slab avalanches are possible. As the snowpack gets deeper, obvious signs of instability will be less forthcoming prior to an avalanche, a conservative mindset is advisable this season due to persistent weak layers buried near the ground. Today, avoid wind-loaded avalanche terrain and the runouts below. The danger is CONSIDERABLE on wind-loaded slopes and MODERATE on all others.&nbsp;</p>

<p>Eleven inches of snow fell last night in Cooke City equal to 1.1” of SWE and southwest winds gusting to 60 mph are readily drifting recent snow into slabs that will avalanche under the weight of a skier or rider today. Larger, deep-slab avalanches like last week’s slide on Crown Butte (<a href="https://www.mtavalanche.com/images/21/snowmobile-triggered-slide-crown-…;) or the slide on Mount Abundance two weeks ago (<a href="https://mtavalanche.com/images/21/large-avalanche-mt-abundance"><strong…;) are possible. Avoid steep wind-loaded terrain and avalanche terrain you suspect harbors a shallow, weak snowpack such as thin, rocky areas in high-elevation starting zones or lower-elevation slopes that generally receive less snow. An example of a lower elevation slope is Town Hill, where skiers triggered a collapse that spooked them into avoiding steep terrain 3-days ago (<a href="https://www.mtavalanche.com/node/24369"><strong>details</strong></a&gt;). The danger is rated CONSIDERABLE on wind-loaded slopes and MODERATE on all others.&nbsp;</p>

<p>The Southern Gallatin Range, Southern Madison Range, and Lionhead area received 2-4” of new snow in the last 24-hours equal to 0.2-0.3” of SWE. A layer of weak facets and sugary depth hoar near the ground makes large, human-triggered avalanches possible. Skiers near Specimen Creek observed natural avalanche activity over the weekend and triggered two large collapses indicating that human-triggered avalanches on steep slopes remain possible (<a href="https://mtavalanche.com/images/21/natural-avalanche-specimen-creek"><st…;). Gusts of 40 mph from the southwest are depositing slabs of wind-drifted snow onto slopes that add weight and increase the likelihood of triggering an avalanche. Evaluate the terrain and snowpack carefully prior to considering skiing or riding on steep slopes. The danger is MODERATE.</p>

<p>If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong>website<…;, email (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

<p>Strong winds gusting into the 70s mph are loading snow into dense slabs are keeping the snowpack in the Bridger, Northern Madison, and Northern Gallatin Ranges on edge. During routine inbounds, avalanche mitigation work, the Bridger and Big Sky Ski Patrols noted fresh drifts of wind-loaded snow avalanching up to 12-14” deep and the Big Sky Ski Patrol saw two new avalanches in the backcountry that broke on deeply buried weak layers. Similar wind-slabs in the backcountry will likely break 1-2’ deep and outliers like Saturday’s 10’ deep snowmobile-triggered avalanche in McAtee Basin are possible (<a href="https://mtavalanche.com/images/21/large-avalanche-mcatee-basin"><strong…;, <a href="https://www.youtube.com/watch?v=65JO-4w4qXo"><strong>video</strong></a&…;). While climbing yesterday, Doug said he “would not entertain getting in the wind-loaded gullies in Hyalite”.</p>

<p>Notable avalanche activity in the last week:</p>

<ul>
<li>Natural avalanche in the Northern Madison Range yesterday (<a href="https://mtavalanche.com/images/21/natural-avalanche-northern-madison-ra…;)</li>
<li>Natural slide on the ridge north of Mount Blackmore Saturday or Sunday (<a href="https://mtavalanche.com/node/24388"><strong>details and photo</strong></a>)</li>
<li>3.5’ deep, snowmobile-triggered avalanche at the entrance to McAtee Basin on Saturday (<a href="https://mtavalanche.com/images/21/snowmo-triggered-avalanche-entrance-m…;)</li>
<li>Very large, natural avalanches late last week on Mount Blackmore (<a href="https://www.youtube.com/watch?v=Ychm42ihtjk&amp;list=PLXu5151nmAvQDzKmH…;, <a href="https://www.mtavalanche.com/node/24345"><strong>photos and details</strong></a>), Alex Lowe Peak (<a href="https://www.mtavalanche.com/images/21/natural-deep-slab-lowe-peak-2"><s…;), and on Flanders Mountain (<a href="https://www.mtavalanche.com/node/24364"><strong>photos and details</strong></a>)</li>
<li>Large, natural avalanche breaking near the ground south of Bridger Bowl (<a href="https://www.mtavalanche.com/node/24324"><strong>photos</strong></a&gt;)</li>
<li>A fatal avalanche in Beehive Basin last Sunday (<a href="https://mtavalanche.com/node/24274"><strong>details and information</strong></a>)</li>
</ul>

<p>Avoid travel on or below steep, wind-loaded slopes where the danger is rated CONSIDERABLE and human-triggered avalanches are likely. Human-triggered slides are possible on steep, non-wind-loaded slopes and the danger is MODERATE.</p>

<p>The Southern Gallatin Range, Southern Madison Range, and Lionhead area have a layer of weak facets near the ground that heighten the avalanche danger and make large, human-triggered avalanches possible. Skiers in the Southern Gallatin Range yesterday noted a recent natural avalanche and two large whumphs (<a href="https://mtavalanche.com/images/21/natural-avalanche-specimen-creek"><st…;). While there was not as much new snow or wind, the weak structure of the snowpack makes large, deep-slab avalanches possible. Pay special attention to slopes with recent drifts that add weight and stress to the snowpack and utilize a conservative mindset during a season plagued by deeply buried instabilities. The avalanche danger is MODERATE.</p>

<p>Light snowfall continued in the mountains around Cooke City with 2-3” new in the last 24-hours. This snow will be blown into soft wind-slabs sensitive to human-triggers. Larger avalanches breaking deeper into drifted snow and slides initiating in the thinner, weaker snowpacks that exist in some starting zones are possible. See my <a href="https://www.youtube.com/watch?v=tzo-kbMbDUc"><strong>video </strong></a>from last week for further discussion about this or look at the <a href="https://www.mtavalanche.com/images/21/snowmobile-triggered-slide-crown-… </strong></a>of the snowmobile-triggered avalanche on Crown Butte from last Thursday for a recent example. A skier on Town Hill got a large collapse yesterday that clearly indicates this persistent, though limited, problem is still with us (<a href="https://www.mtavalanche.com/node/24369"><strong>details</strong></a&gt;). Human-trigger avalanches are possible and the danger is rated MODERATE. Evaluate the snowpack and terrain carefully to identify and avoid areas of concern. As snowfall intensifies today, the avalanche danger will increase. Look for signs of increasing instability and adjust travel plans accordingly.</p>

<p>If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong>website<…;, email (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>