Noticed crown and debris on drive up Bridger Canyon this morning. Looks like a wind slab.
<p><span><span><span><span><span><span>Springtime weather brings several avalanche problems that will evolve throughout the day as temperatures warm well above freezing. Consider what avalanche problem is the most concerning at any given time and where they might overlap, because the management strategy is slightly different for each. </span></span></span></span></span></span></p>
<p><span><span><span><strong><span><span>Wind slab avalanches </span></span></strong></span></span></span><span><span><span><span><span><span>breaking up to a couple feet deep on slopes where winds recently drifted snow are the primary concern. Yesterday, a natural avalanche slid on a wind-loaded slope on the Fin south of Cooke City (</span></span></span></span></span></span><a href="https://mtavalanche.com/node/34742"><span><span><span><strong><span><u>… and photo</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). While instability related to recently wind-drifted snow is decreasing, similar human-triggered avalanches are possible today. Seek out sheltered terrain and avoid heavily wind-loaded slopes immediately below cornices. Note conditions that indicate potential instability, such as a stiffening of the snow surface and shooting cracks. </span></span></span></span></span></span></p>
<p><span><span><span><strong><span><span>Wet loose avalanches </span></span></strong></span></span></span><span><span><span><span><span><span>will slide naturally as the day warms and the snow surface moistens and becomes weaker. These are most likely on southern aspects and slopes with exposed rocks and cliff bands that heat up in the sun. Wet snow avalanches will be relatively small, primarily a hazard in technical terrain where heavy snow could push riders or skiers into obstacles like trees, rocks and off cliffs. Move to shadier, northern aspects if more than the top few inches of snow becomes wet or you observe cinnamon-roll-like pinwheels and small wet snow avalanches in nearby terrain. </span></span></span></span></span></span></p>
<p><span><span><span><strong><span><span>Persistent slab avalanches </span></span></strong></span></span></span><span><span><span><span><span><span>are primarily a concern in the Lionhead, Southern Gallatin and Southern Madison Ranges, and to a lesser extent, the mountains around Cooke City. While not likely, human-triggered avalanches could break 2-3 feet deep and over one hundred feet wide on buried weak layers. This weekend, a natural avalanche broke on this layer in the Sheep Creek drainage (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/natural-avalanche-north-cooke-cit…;), and my partner and I noted the issue in several snowpack assessments over the last two days around Cooke City (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/ectp18-absarokas"><span><span><sp…;, </span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=t7oJF2TPrXI&list=PLXu5151nmAvToI_ir…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34732"><span><span><span><strong><span…;). Saturday and Wednesday of last week, snowmobilers triggered avalanches in the Taylor Fork that broke several feet deep (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34722"><span><span><span><strong><span…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34697"><span><span><span><strong><span…;). Reduce your vulnerability by selecting smaller, less consequential slopes with fewer terrain traps and by following safe travel practices. Digging and testing the snowpack increases your chances of catching critical instability before it catches you. </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Human-triggered avalanches are possible, and the danger is rated MODERATE across the forecast area. </span></span></span></span></span></span></p>
Temps around 32 degrees
As we rode, we dug a few snowpits looking for the weak layer that we found yesterday buried about 2 feet deep. While we were able to find this layer, we only got propagation in one of three tests (ECTP 26, E aspect, 9070'). Photo: GNFAC
We noted one avalanche on the Fin that likely occurred yesterday or early this morning from a wind slab or cornice fall. Photo: GNFAC
Today, Dave and I did the full mechanized boundary tour north of Cooke City. We rode up and over Daisy Pass towards Wolverine Pass and Mount Abundance, up Lulu Pass, to the Goose Lake boundary, and back out through Round Lake.
In thirty miles of riding, we noted one avalanche on the Fin that likely occurred yesterday or early this morning from a wind slab or cornice fall. That being said, low cloud cover obscured views and the light was relatively flat all day. What was visible were strong winds transporting snow, especially at high elevations. We chose to stay out of steep upper elevation bowls that are regularly wind loaded and out from under corniced ridgelines.
As we rode, we dug a few snowpits looking for the weak layer that we found yesterday buried about 2 feet deep. While we were able to find this layer, we only got propagation in one of three tests (ECTP 26, E aspect, 9070').
Throughout the day, the snow surface became denser and denser. The little precipitation that fell was noticeably rimed and when we rode back into Cooke City around 1pm it was nearly 40 degrees in town. Driving out of Cooke and into the Lamar Valley, we saw a good number of wet loose avalanches breaking in steep, cliffy terrain just south of the road.
Looking ahead, we are preparing for a sudden shift in the weather with above-freezing temperatures into the alpine and direct sunshine. We are keeping an eye on wind slab avalanches at upper elevations, but will start to shift our focus towards the potential for wet snow avalanche problems in the coming days.
Fin had a slide on it today. I was too cloudy to tell if it was released naturally or not.
<p><span><span><span><span><span><span>Near Cooke City strong winds have drifted 5” of new snow and snow from last week into stiff slabs that can avalanche under the weight of a person. These </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>are the primary concern, and today the wind will continue to build slabs and create dangerous conditions on wind-loaded slopes. Additionally, a weak layer buried 2 feet deep below last week’s snow can produce larger </span></span></span></span></span></span><span><span><span><strong><span><span>persistent slab</span></span></strong></span></span></span><span><span><span><span><span><span> </span></span></span></span></span></span><span><span><span><strong><span><span>avalanches</span></span></strong><span><span><span>, even on non-wind-loaded slopes. A natural avalanche appeared to break on this layer a couple days ago in Sheep Creek (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/natural-avalanche-north-cooke-cit…;), and yesterday Dave and Haylee found it in snowpits with unstable test results (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/ectp18-absarokas"><span><span><sp…;, </span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=t7oJF2TPrXI&list=PLXu5151nmAvToI_ir…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34732"><span><span><span><strong><span…;). Avoid big, wind-loaded slopes and dig down 2-3 feet to assess the snowpack for recently buried weak layers. Be cautious crossing below steep slopes because the recently buried weak layer creates potential to trigger a slide from flatter terrain. </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>The avalanche danger is CONSIDERABLE on wind-loaded slopes and MODERATE on all other slopes around Cooke City.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Near Bozeman, Big Sky, West Yellowstone and Island Park, </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> are the primary concern where strong winds have drifted last week’s snow into slabs up to a couple feet thick. Be cautious of recently wind-loaded slopes, often identifiable by a textured or rounded snow surface, and typically found near ridgelines below cornices.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Above freezing temperatures, and any rain, will melt the snow surface and make </span></span></span><strong><span><span>wet loose avalanches</span></span></strong><span><span><span> possible. These slides will probably be small today, and most hazardous if they knock you over in terrain above cliffs or rocks. Feel for a moist snow surface as a sign wet snow danger is rising, and find lower angle or colder slopes. </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Near West Yellowstone, including the southern Madison and southern Gallatin ranges, a person can trigger </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>2-4 feet deep on a weak layer that was buried in January. Avalanches were triggered on this layer in the Taylor Fork on Saturday (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34722"><span><span><span><strong><span…;) and Wednesday (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34697"><span><span><span><strong><span…;). These slides have not been huge, but large enough to be deadly, especially in terrain similar to where they have occurred. They broke on slopes with thick trees that could cause trauma, or depressions at the bottom where snow can pile up deep. Select terrain with minimal terrain traps like trees, cliffs or gullies.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>There is also a chance for slides to break a couple feet deep below last weekend’s snow. Last weekend we saw layers break in stability tests below the new snow near West Yellowstone (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34670"><span><span><span><strong><span…;) and Island Park (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34631"><span><span><span><strong><span…;). Dig down a couple feet to check for potential weak layers.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Human-triggered avalanches are possible and the avalanche danger is MODERATE near Bozeman, Big Sky, West Yellowstone and Island Park.</span></span></span></span></span></span></p>
