Feb 7 We saw a couple storm slabs that broke in today's snow 4-6" deep, 10-30' wide, and we triggered one 3-4" deep wind slab, "remotely", from a few feet back on a small ridgeline. R2-D1. These slabs were very soft, F- to F hard. Photo: GNFAC
Feb 7 We saw a couple storm slabs that broke in today's snow 4-6" deep, 10-30' wide, and we triggered one 3-4" deep wind slab, "remotely", from a few feet back on a small ridgeline. R2-D1. These slabs were very soft, F- to F hard. Photo: GNFAC
We rode below the Throne and towards Fairy Lake, mostly at elevations 6,800-7,500'. It snowed steady S1-2 most of the day and tapered off in the afternoon. Wind was a stout moderate out of the east and south in the parking lot. Wind was light to moderate out of the south up higher/"mid-mountain". There was a brief clearing mid-day and we could see the bowl and ridge south of Naya Nuki.
We saw a couple storm slabs that broke in today's snow 4-6" deep, 10-30' wide, and we triggered one 3-4" deep wind slab, "remotely", from a few feet back on a small ridgeline. R2-D1. These slabs were very soft, F- to F hard.
The interface below this week's storm was generally well bonded to the surface below and lacked a weak layer from the recent high pressure. I would not totally rule out the potential of something breaking wider on a weak layer because we did not get a good look at higher elevations, but so far it seems less likely to have a persistent slab problem involving a layer below this week's snow in the Bridgers as compared to other parts of our forecast area.
At the base of G2 I triggered a 3 inch x 100 foot soft slab. I was surprised how far it propagated. It looked like it failed on a density change under the morning's new snow. 40 feet up on the first large bench we triggered another slide, 6 inches deep, the entire width of the bench. It could have pushed a climber off if they were in the middle of it. It was snowing steady (1"/hr) and wind was minimal, but a few hours later we could see plumes higher up in the gullies.
It had such zip to the propagation that I'm thinking it might take a day for it to not be reactive. There was no way we wanted to get on anything open and steep.
At the base of G2 I triggered a 3 inch x 100 foot soft slab. Photo: D Chabot
At the base of G2 I triggered a 3 inch x 100 foot soft slab. I was surprised how far it propagated. It looked like it failed on a density change under the morning's new snow. 40 feet up on the first large bench we triggered another slide, 6 inches deep, the entire width of the bench. It could have pushed a climber off if they were in the middle of it. It was snowing steady (1"/hr) and wind was minimal, but a few hours later we could see plumes higher up in the gullies.
It had such zip to the propagation that I'm thinking it might take a day for it to not be reactive. There was no way we wanted to get on anything open and steep.
<p><span><span><span><span><span><span>It’s been a wild week of unusual weather - with hurricane force winds, winds blowing from unusual directions, both very warm and very cold temperatures (sometimes right next to each other with crazy strong temperature inversions), and periods of rapid snowfall. This all came after some new weak layers formed and it has left us with quite a variable snowpack.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Now it’s snowing again. This will both add load to the snowpack and make it harder to visually identify what’s been going at the snow surface over the last week (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=pwAambVPOeg"><span><span><span><span><s…’s video</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span> from Blackmore yesterday).</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Unusual weather leads to unusual avalanches. This has certainly been the case over the last couple days. </span></span></span></span></span></span></p>
<ul>
<li><span><span><span><span><span><span>On Wednesday, Big Sky Ski Patrol intentionally triggered an avalanche with explosives on a slope loaded by the strong south winds that broke up to 7 feet deep, breaking on the old snow surface from dry weather in late January. They haven’t seen an avalanche like that on that slope in 40-50 years. (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34027"><span><span><span><span><span><…;, </span></span></span></span></span></span><a href="https://www.kbzk.com/news/local-news/avalanche-triggered-during-mitigat… story</span></span></u></span></span></span></span></span></a></li>
<li><span><span><span><span><span><span>Also on Wednesday, skiers triggered many storm slab avalanches in the new snow at low elevations on </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34015"><span><span><span><span><span><…. Ellis</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span> and in the </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34013"><span><span><span><span><span><… Range</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>.</span></span></span></span></span></span></li>
<li><span><span><span><span><span><span>There have also been plenty more typical avalanches on wind-loaded slopes below ridgelines across the advisory area (examples from near Cooke City (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/avalanche-north-crown-butte"><spa…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/scotch-bonnet-north-avalanche"><s…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/natural-avalanche-mt-henderson-ne…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/natural-avalanche-miller-ridge-ne…;), </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/33978"><span><span><span><span><span><…;, and the </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/wind-slab-crown-hourglass-couloir…;).</span></span></span></span></span></span></li>
</ul>
<p><span><span><span><span><span><span>Very strong winds and winds from unusual directions (out of the east) have loaded slopes that aren’t usually loaded, so be on alert for wind loading everywhere. Additionally, be on alert for slides on lower elevation slopes that usually aren’t much of a concern. In some cases, with the strong inversions mid-week, they may have touchier conditions than higher elevation slopes (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34031"><span><span><span><span><span><…;). </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>With lots going on in the snowpack and it being loaded again, avalanche conditions are dangerous and cautious route-finding is required. Avalanches could break as </span></span></span></span></span></span><span><span><span><strong><span><span>Wind Slabs</span></span></strong></span></span></span><span><span><span><span><span><span> either in the new snow or from snow drifted earlier in the week, </span></span></span></span></span></span><span><span><span><strong><span><span>Storm Slabs</span></span></strong></span></span></span><span><span><span><span><span><span> as snow piles up during intense precipitation today, or</span></span></span></span></span></span><span><span><span><strong><span><span> Persistent Slabs</span></span></strong></span></span></span><span><span><span><span><span><span> on the weak layers that formed during the dry period in late January.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Today, the avalanche danger is CONSIDERABLE.</span></span></span></span></span></span></p>
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