Triggered a small slide (r2 d2) in a north east facing chute at around 8300 ft. Photo: J Alford
24-25
Triggered a small slide (r2 d2) in a north east facing chute at around 8300 ft. Photo: J Alford
Avalanche Details: Wind/storm slab avalanche in the Bridger Range
Bridger Range, 2024-12-17
Republic Creek Observation
Date
From email: "Steve Harvey and I did a quick pit yesterday (12/16/2024) S. of Cooke in Republic Creek. E. aspect; 9.085'; 30° slope; HS 80 c; 12:30PM, Calm/cool (teens), Lt snow.
ECTN21; ECTP24 at 50 cm on buried facets. We declined to continue on slope.
We didn't perform a detailed profile, but generally, fist (new snow) and 4-finger above buried facets and progressively 2-finger to 1-finger below.
Noticeable Issues:
(1) Low and variable snowpack, 30cm or less under/near trees and on wind-scoured aspects and loading in fetch zones. Something to keep in mind as season progresses with potential sweet spots in predictable places.
(2) Buried 50 cm facets/hoar that is essentially everywhere in Cooke City zone.
(3) We did not observe buried deep facets at the base of the snowpack."
Region
Cooke City
Location (from list)
Republic Creek
Observer Name
Jesse Logan
Wind/storm slab avalanche
Date
Activity
Skiing
Triggered a small slide (r2 d2) in a north east facing chute at around 8300 ft. The slide was triggered on a ski cut through a wind loaded drift and propagated about 15 or 20 ft wide. It about 6 in deep on the edges and two feet in the loaded area. We observed several other signs of instability throughout the day, most wind loaded terrain was touchy and easy to rip off with slabs anywhere from 6 in deep to two or three feet deep. All signs of instability originated from the interface between the new snow from the last few days and facets from the last high pressure system.
Region
Bridger Range
Observer Name
Jay Alford
Persistent Slab Instability
Date
Activity
Skiing
Around 5" of fresh snow lay on top of the snowmobiles this morning in Cooke City. We rode up to Daisy Pass to visualize terrain and got eyes on Crown Butte. On the north side, we noted the crown of a wind slab avalanche (R1 D1) that broke during the storm cycle. We then rode back down and toured up Henderson Mountain along its SW flank. Skies cleared throughout the day and allowed for great visualization of terrain north of Cooke. We got eyes on Miller Ridge, Crown Butte, Henderson Bench, Scotch Bonnet and Sheep Mountain; we did not note any other avalanches outside of the small one up on Crown Butte. We saw extensive cross-loading in the bowl of Henderson Mountain and on Miller Ridge.
We dug snowpits on SW and S aspects on Henderson. We noted buried facets a little over a foot deep on our pit on the SW and we got an unstable test result in our snowpit on the S aspect (ECTP 25) on a facet/melt freeze crust sandwich.
Most notably, as we entered non wind-effected, upper-elevation terrain on Henderson, we consistently triggered many localized collapses and heard audible whumpfs, indicating persistent slab instability.
Region
Cooke City
Location (from list)
Henderson Mountain
Observer Name
H. Darby
Skier caught and buried at Bridger
Bridger Bowl
Bridger Range
Code
SS-R3-D2-S
Aspect
E
Latitude
45.82310
Longitude
-110.92600
Notes
From Bridger Bowl: "On December 15th, 2024 at 12:09 p.m., a skier in open terrain was caught and buried by an avalanche in the Papa Bear region below Bridger Gully. The skier, who was with a partner, was buried just below the snow surface and was able to punch a hole up through the top of the snow. The skier's partner and other members of the skiing public responded quickly and were able to extricate the uninjured skier.
Although rare, inbounds avalanches may happen and are defined in the skier's responsibility code as an inherent risk of skiing, even within ski area boundaries. We share this as a reminder of the importance of skiing and riding with a partner, especially in deep snow conditions."
Notes about snowpack:
Slide was 8 inches deep, 450 feet wide, and broke within the storm snow 2 inches above the new snow/old snow interface. Trigger unknown.
The Alpine weather station received 2.5" snow = 0.2" SWE from 2200 on 12/14 to 0300 on 12/15, then intense snowfall from 0700 to 1200 added 7" and 1"SWE for a storm total of 9.5"=1.2"SWE over 14 hours as of noon.
Number caught
1
Number buried
1
Avalanche Type
Soft slab avalanche
R size
3
D size
2
Bed Surface
S - Avalanche released within new snow
Problem Type
Storm Slab
Slab Thickness
8.0 inches
Vertical Fall
600ft
Slab Width
450.00ft
Weak Layer Grain type
Precipitation Particles
Slab Layer Grain Type
Precipitation Particles
Images
Snow Observation Source
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year
GNFAC Avalanche Forecast for Tue Dec 17, 2024
Snowpack and Avalanche Discussion
<p><span><span><span>Dangerous avalanche conditions exist across the advisory area. New and wind-drifted snow are loading weak layers buried 1-2 feet deep and human-triggered avalanches are likely. Reduce or eliminate exposure to slopes steeper than 30 degrees until the snowpack has time to adjust to recent snowfall. Traveling in and around avalanche terrain requires careful snowpack evaluation, cautious route-finding and conservative decision-making.</span></span></span></p>
<p><span><span><span><strong>Three-Day Storm Totals: </strong></span></span></span></p>
<ul>
<li><span><span><span>Bridger Range, Cooke City, Island Park and Big Sky - 15-22” (1.3-2.0” SWE)</span></span></span></li>
<li><span><span><span>West Yellowstone, Taylor Fork and Hyalite Canyon - 8-12” (0.6-1.2” SWE)</span></span></span></li>
</ul>
<p><span><span><span><strong>Wind slab avalanches </strong>failing 1-3 feet deep are likely today. Avoid slopes with visual clues of recent drifting and commonly wind-loaded areas near ridgelines, below cornices and in gullies. Indicators of wind slab instability include recent avalanche activity, shooting cracks and a stiffening of the snow surface. Yesterday, my partner and I visited the site of a wind slab avalanche in Cooke City that broke 3 feet deep and 100 feet wide on Sunday as a group skied past (<a href="https://youtube.com/shorts/npOK4d94H50"><strong><span>video</span></str…;). Recent snow and wind had reloaded the slope, and it was ready to avalanche again. Expect a similar story throughout the advisory area. </span></span></span></p>
<p><span><span><span>On Sunday, riders in the West Yellowstone and Island Park areas reported <strong>persistent slab avalanches </strong>failing on buried weak layers near Two Top (<a href="https://www.mtavalanche.com/node/32430"><strong><span>details and photos</span></strong></a>), and a group on Mount Blackmore triggered a large <em>whumphing </em>collapse (<a href="https://www.mtavalanche.com/node/32443"><strong><span>details</span></s…;). Weak layers buried 1-2 feet deep exist across the forecast area (<a href="https://youtube.com/shorts/CdNOdERCQgc"><strong><span>Cooke City</span></strong></a>, <a href="https://www.youtube.com/watch?v=wDsq1f-KVUg&list=PLXu5151nmAvToI_ir… Ridge</span></strong></a><strong>, </strong><a href="https://www.youtube.com/watch?v=CCd4OIw-4IU&list=PLXu5151nmAvToI_ir… Fork videos</span></strong></a>). Recent avalanche activity, whumphs, and shooting cracks are bullseye indicators of instability. </span></span></span></p>
<p><span><span><span><strong>Notable Recent Avalanche Activity Since Sunday </strong>(all reported activity on<strong> </strong><a href="https://www.mtavalanche.com/avalanche-activity"><strong><span>log</span…;)<strong>: </strong></span></span></span></p>
<ul>
<li><span><span><span>Many natural avalanches on Saddle Peak and in Argentina Bowl (<a href="https://www.mtavalanche.com/node/32464"><strong><span>details</span></s…;) </span></span></span></li>
<li><span><span><span>Remotely triggered wind slab avalanche on Henderson (<a href="https://www.mtavalanche.com/node/32441"><strong><span>details</span></s…;, <a href="https://www.mtavalanche.com/node/32474"><strong><span>GNFAC ob</span></strong></a>)</span></span></span></li>
<li><span><span><span>Persistent slab avalanche near Island Park (<a href="https://www.mtavalanche.com/node/32422"><strong><span>details</span></s…;) </span></span></span></li>
<li><span><span><span>Collapsing, cracking, and a remotely triggered storm snow avalanche in Beehive (<a href="https://www.mtavalanche.com/node/32423"><strong><span>details</span></s…;, <a href="https://www.mtavalanche.com/node/32438"><strong><span>details</span></s…;)</span></span></span></li>
<li><span><span><span>Skier triggered storm slab avalanche on The Throne (<a href="https://www.mtavalanche.com/node/32444"><strong><span>details</span></s…;)</span></span></span></li>
</ul>
<p><span><span><span>Avalanche danger is CONSIDERABLE on all slopes.</span></span></span></p>
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