Observed a large avalanche on a west facing slope approx 10000ft, with a higher crown at 10200'. Crown depth 4-6'. HS-Ns-D2-R2-O . Ran 1000ft and into terrain I had previously considered safe.
Toured into the basin NE of Ross Peak this afternoon.
Snow depth in the basin was 115cm. Winds predominantly from the SW.
Light to moderate snowfall throughout the afternoon.
No avalanche activity noted, but much of the ridge line was obscured by clouds.
No collapsing or crack propagation seen.
Headed out to the throne today. Had light to moderate winds from the west blowing all day long at all elevations. Found heavily wind affected skiing in open meadows and softer snow in the trees. Stayed out of avalanche terrain and found no signs of instability. Snow was visibly being transported all day.
Toured up Sheep Creek Trail on the West side of the Lionhead Range on 1/11/2025. We heard whoomphing through out our tour in. We stopped counting after 12. Some of these whoomphs seemed relatively far away and very loud. We could not tell if these farther whoomphs were triggered by us. We were the only ones in our location but we did hear snowmobiles in another location near the trailhead. We also felt multiple large collapses on very low angle slopes and skinning across non consequential terrain.
We dug a pit on an East facing aspect below the slope we had planned to ride. The height of snow was about 110 cm and there was a very concerning layer of large facets at 75cm deep going to the ground. There were no other layers of concern in the snowpack we found and the rest of the snowpack was right side up. Our results were CT17 SPQ2 and ECTP26 SCQ1. Bother failures during tests were on the layer of facets and on the CT and ECT our columns easily separated from the facet layer after failure. Due to these observations we opted not to ride our objective and followed our skin track back out to the trailhead.
<p><span><span><span><span><span><span>New snow and wind are creating dangerous avalanche conditions and human triggered avalanches are likely. One to two feet of low density snow fell since Friday and more is expected today. Moderate to strong wind out of the west and northwest the last couple days drifted this new snow, and snow from earlier in the week, into thick slabs that will be easy for a person to trigger. Wind decreased this morning, but it won’t take much to drift the low density new snow and continue to build wind slabs and add weight over buried weak layers. </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> are the primary concern, and they could break 1-3 feet deep and be large enough to bury or injure a person. Wind Slabs were already seen breaking naturally the last couple days (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/33472"><span><span><span><span><span><… and photos</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span> from Friday, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/33503"><span><span><span><span><span><… and photo from yesterday</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span> near Mt. Blackmore). Avalanches could break deeper on buried persistent weak layers near the bottom of the snowpack. These </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> could be very large and destructive. While we have not seen many of these avalanches yet in the mountains near Bozeman and Big Sky, the snow structure does exist and should not be trusted while the new snow and wind are stressing the snowpack (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/33442"><span><span><span><span><span><… of buried weak layers</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>). </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Avoid slopes steeper than 30 degrees and the flatter runout zones below. Human-triggered avalanches are likely and the avalanche danger is CONSIDERABLE.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Near Cooke City, West Yellowstone and Island Park the primary concern is avalanches breaking on weak layers near the bottom of the snowpack. Over the last week near Cooke City, </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> 4-6’ deep broke naturally and some were possibly triggered from flat terrain a long distance away (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/fresh-persistent-slab-south-mt-ab…. Abundance photo</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/persistent-slab-above-henderson-b… Mtn. photo</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/older-persistent-slab-fisher-mtn-… Mtn. photo</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>). Snowfall rates decreased since earlier in the week, but the mountains have had snow nearly every day for over two weeks. </span></span></span></span></span></span><span><span><span><strong><span><span>And, the winds increased the last few days</span></span></strong></span></span></span><span><span><span><span><span><span> </span></span></span></span></span></span><span><span><span><strong><span><span>which is usually what really pushes the snowpack to its breaking point</span></span></strong></span></span></span><span><span><span><span><span><span>. These winds formed thick drifts which add weight to buried weak layers, and are a significant hazard on their own. </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> can be triggered where recent drifts formed and can be large enough to bury or injure a person (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/deep-wind-slab-henderson"><span><… of recent wind slab avalanche</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><span><span><span>With continued snow and wind, dangerous persistent slab or wind slab avalanches are likely for a person to trigger today, especially on wind-loaded slopes. On slopes without previous wind-loading, persistent slab avalanches are still possible, but the snowpack has started to get a break from stress without the weight of recent drifts. </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Cautious route finding is key today. Find terrain sheltered from the wind that has minimal hazards like cliffs, trees and gullies, or keep it simple by staying on slopes less than 30 degrees, and avoiding runout zones below steep, wind-loaded slopes. The avalanche danger is CONSIDERABLE on windloaded slopes and MODERATE on all other slopes.</span></span></span></span></span></span></p>
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BBSP measured 11.5"/0.95" SWE at 4pm (24 hr total) top Bridger, then it snowed 5" overnight. Alpine and Brackett not showing as much.
Bavaria at Big Sky shows 12"+ since yesterday morning.
A wind slab avalanche was seen just below Two Top. This appeared to be a natural slide although tracks can be seen above and to the left of the crown. This was on a northeast facing slope that was wind loaded. The avalanche appeared to be fresh after recent snow. Photo: C Barnhart
