Very obvious wind loading. Had very large collapse on skin track. About a 3.5 foot deep snow pack. Shallow and faceted at the bottom.
<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&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>)</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>). 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>
From Obs: "Driving back from Grotto Falls trailhead, from the east side of the reservoir I could see this slide on the ridge that extends north from Blackmore above Blackmore lake. The slide was on a north-facing slope around 9,100', large enough to see with the naked eye and clear as day with binoculars. The crown looked multiple feet deep and either meandered, partially hidden from view, by another ridge or a substantial second avalanche a hundred feet away."
From Obs: "This slide on the ridge extends north from Blackmore above Blackmore lake. The slide was on a north-facing slope around 9,100'. The crown looked multiple feet deep and either meandered, partially hidden from view, by another ridge or a substantial second avalanche a hundred feet away."
Driving back from Grotto Falls trailhead, from the east side of the reservoir I could see this slide on the ridge that extends north from Blackmore above Blackmore lake. The slide was on a north facing slope around 9,100', large enough to see with the naked eye and clear as day with binoculars. The crown looked multiple feet deep and either meandered, partially hidden from view, by another ridge or a substantial second avalanche a hundred feet away.
Stable snowpack between hangover and upper green sleeves (ugs) while hiking. As soon as we crossed into the wind loaded gully we experienced increasingly slabby snow structure with failure. No snow pits or stability tests
From obs: "Observed 2 natural avalanches, both on the basal persistent layer I would guess. one maybe a week old, partially filled in (SS-N-D1R2-O), and one that ran in the last 24 hrs (SS-N-D1.5R2-O) on a SE aspect, 35 deg at 8200 ft. I thought it was interesting given the lack of new snow and seeming lack of strong winds in this area. 2/5 ECTs had propagation, we had two large collapses."
From obs: "Observed 2 natural avalanches, both on the basal persistent layer I would guess. one maybe a week old, partially filled in (SS-N-D1R2-O), and one that ran in the last 24 hrs (SS-N-D1.5R2-O) on a SE aspect, 35 deg at 8200 ft. I thought it was interesting given the lack of new snow and seeming lack of strong winds in this area." Photo: S. Hennessey
From email: "Observed natural deep slab probably happened overnight with the strong winds... snowpack in the area was about 3-5’ deep mostly 4F with 20+cm of F depth hoar at the bottom... obviously not strong enough to support the windload."
