23-24
Wind slabs in Frazier
Date
Activity
Skiing
Skied into Frazier basin today. Triggered a few small windslabs and saw a lot of cracking on NW aspects. All windslabs were still small breaking a few inches deep 10-15 feet wide and only running short distances in steep terrain. Winds were strong from the NE all morning and still blowing hard and continuing to load slopes when we left at 12:30.
Region
Bridger Range
Location (from list)
Frazier Basin
Observer Name
Charlie Bayles
GNFAC Avalanche Forecast for Tue Mar 26, 2024
Snowpack and Avalanche Discussion
<p>Three-day snow totals are creeping up and incrementally loading a snowpack that has repeatedly demonstrated an inability to handle much weight without breaking. Since Saturday, snow in the mountains around Bozeman, Big Sky and Island Park totaled 7-11", equal to 0.6-0.9” of <a href="https://avalanche.org/avalanche-encyclopedia/#snow-water-equivalent-swe… water equivalent (SWE)</span></a> (Big Sky is the winner). There is less new snow in the mountains near Cooke City and West Yellowstone, totaling around 4”, equal to 0.4-0.5” of SWE. While we don’t expect a widespread cycle of deep, tree-snapping slides with current snow loads, more snow is forecast today, and a large avalanche breaking deep in the snowpack should not be shocking. Avalanches within the new and wind-drifted snow are more likely and will be large enough to bury or injure skiers and riders, especially in the presence of terrain traps such as trees, cliffs, gullies, and rocks.</p>
<p>Deep avalanches failing on persistent weak layers will result from one of two scenarios. First, a natural or human-triggered wind-slab avalanche or cornice fall could trigger a deeper slide. Second, a backcountry traveler could get unlucky and cross a thinner area in the snowpack, triggering the whole slope. Regardless of how the avalanche initiates, getting caught in a slide breaking 3-6 feet deep and hundreds of feet wide is more easily fatal than not. The last avalanche of this sort occurred seven days ago on Mount Blackmore and resulted in a helicopter evacuation by Gallatin County Search and Rescue (<a href="https://www.mtavalanche.com/node/31526"><strong><span>details</span></s…;). Accurately testing for deep slab instability with a snowpit is difficult to impossible. Regional observation over the course of a storm is the best proxy for understanding what is possible at the slope scale (<strong><a href="https://www.mtavalanche.com/avalanche-activity">avalanche activity list</a></strong>). Conservative terrain selection is the right course of action while the snowpack is getting loaded.</p>
<p>Slab avalanches breaking 6-18” deep within the new and wind-drifted snow are more likely. These instabilities often appear in snowpits or with signs such as recent avalanche activity or shooting cracks. Yesterday, a snowboarder in Cooke City intentionally triggered a wind-loaded slope that broke 10” deep and 30 feet wide (<a href="https://www.mtavalanche.com/node/31598"><strong><span>photo and details</span></strong></a>). On Sunday, Alex saw two natural avalanches within the wind-drifted snow and intentionally triggered a small slide on a test slope (<a href="https://www.youtube.com/watch?v=LlLu6b2UzU8"><strong><span>video</span>…;). Avoid large, wind-loaded slopes and cornices.</p>
<p>If you are considering traveling in avalanche terrain today, choose simpler, less steep slopes sheltered from the wind and without terrain traps. The danger is rated MODERATE.</p>
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Skiers on 03/24/2024 observed this avalanche at the Playground that happened on 03/20/24. Photo: A. Newman
Avalanche Details: Wet slab north of Texas mdw, Bridgers
Bridger Range, 2024-03-25
Battle Ridge Obs
Date
Activity
Snowmobiling
The snow rangers rode around Battle Ridge, the Throne, and Naya Nuki today. New snow depth ranged from 2" to maybe 4-5" in sheltered/lee locations. Lots of older wet slide debris was visible but no avalanche activity in the new snow. There is a very firm crust in most areas and anything with southern exposure has gotten very thin, including the trail in. We rode through several large mud patches on the way out.
Region
Bridger Range
Location (from list)
Battle Ridge
Observer Name
K. Marvinney
Windslab on Town Hill
Town Hill
Cooke City
Code
SS-ARc-R1-D1-I
Aspect
S
Latitude
45.02560
Longitude
-109.93700
Notes
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Snowboarder
Trigger Modifier
c-A controlled or intentional release by the indicated trigger
R size
1
D size
1
Bed Surface
I - Interface between new and old snow
Problem Type
Wind-Drifted Snow
Slab Thickness
10.0 inches
Vertical Fall
40ft
Slab Width
30.00ft
Images
Snow Observation Source
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year
A snowboarder intentionally triggered a wind-slab avalanche on Town Hill in Cooke City that broke 6-10” deep and approximately 30’ wide. It ran about 40 vertical feet. Photo: R. Youngbar
Avalanche Details: Windslab on Town Hill
Forecast link: GNFAC Avalanche Forecast for Tue Mar 26, 2024
Cooke City, 2024-03-25
Forecast link: GNFAC Avalanche Forecast for Tue Mar 26, 2024
Windslab on Town Hill
Date
Activity
Snowboarding
Today I released a windslab with a ski cut on town hill. 6-10” deep and approximately 30’ wide. It ran about 40 vertical feet.
Location (from list)
Town Hill
Observer Name
Reed Youngbar
Deep Slab in playground
Date
Activity
Skiing
Toured out to the playground Sunday. 2-3" new snow provided good riding on smooth surfaces. HS around 1.5-2M at 8-8500' on North side of compass. Did not plan to dig but after observing a significant deep slab from afar that propagated into shallow angled terrain AND took out ski tracks, I found myself with a hypothesis I could not ignore: Have we transitioned to a wet spring snowpack? I assumed this was a wet slab but needed more information. In fact at this location the snowpack was still dry and we still got stubborn propagation at the basal facets (ECTP25). Very difficult to estimate timing of incident however it stands to reason that loose wet snow came down from above and pulled out this slab; most likely caused by rapid warming and a poor refreeze sometime last week. While not a far running avalanche, it did take out the whole snowpack and deposited 10-15' of debris in the trees. We classified it as HS-N-D2-R2-G
Final thoughts: I have not skied in SW MT much this winter but a few things stood out to me yesterday. Thin, shallow snow equals weak snow. Most slabs are hovering right around the 1M mark, just enough for a human to trigger. Recent activity has pulled out many shallow slopes that I have often wondered over the past decade, "can this avalanche?" This winter has provided me many good images of "sneaker" slopes that are just steep enough to run. Despite the allure of untracked snow, seeing propagation at the ground in late winter has my hackles up and I will be staying out of avalanche terrain (sigh) for the foreseeable future. My suggestion: Go to the Tetons where there is 100" sitting on the deck or stay out of avalanche terrain for now.
Note from GNFAC: This avalanche happened on 03/20/2024: details here.
Region
Bridger Range
Location (from list)
Playground
Observer Name
Andrew Newman