23-24

Windslab on Town Hill

Town Hill
Cooke City
Code
SS-ARc-R1-D1-I
Aspect
S
Latitude
45.02560
Longitude
-109.93700
Notes

A snowboarder intentionally triggered a wind-slab avalanche with a ski cut on town hill in Cooke City. The slide released 6-10” deep and approximately 30’ wide. It ran about 40 vertical feet. 

Number of slides
1
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
Snow Observation Source
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

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

GNFAC Avalanche Forecast for Mon Mar 25, 2024

Snowpack and Avalanche Discussion

<p>Human-triggered avalanches are possible across the advisory area. They are most likely to fail 6-18” deep on steep slopes where the wind has drifted recent snow in thicker slabs. However, the possibility of large avalanches breaking on deeply buried weak layers should continue to drive terrain selection. While these large slides have become less likely, they remain highly consequential, taking out nearly the entire season’s snowpack, breaking many feet deep and hundreds of feet wide.</p>

<p>A week has passed since the last large avalanches failed near the base of the snowpack. These slides broke 3+ feet deep, injured a skier and nearly swept a rider downhill had he not grabbed a tree to avoid getting carried (<a href="https://www.mtavalanche.com/node/31526"><strong><span>Blackmore details and photos</span></strong></a><strong>, </strong><a href="https://www.mtavalanche.com/node/31479"><strong><span>Taylor Fork details and photos</span></strong></a>). It is a mistake to think they are not possible today. Yesterday, a group in the Bridger Range found deep instability in their pit near Ross Peak (<a href="https://www.mtavalanche.com/node/31593"><strong><span>details</span></s…;), and two days ago, a skier triggered a collapse with cracks that shot out 50 feet on Woody Ridge in Cooke City (<a href="https://www.mtavalanche.com/node/31570"><strong><span>details</span></s…;). Go back a bit further on our <a href="https://www.mtavalanche.com/weather/wx-avalanche-log"><strong><span>wea… and avalanche log</span></strong></a><strong> </strong>to read through details about the unusually high number of avalanches breaking on this season’s persistent weak layers (<a href="https://youtu.be/K_t6Fi6wUC4?si=7YL80dNe5pSqJUsL"><strong><span>video</…;). As Doug recently discussed from Saddle Peak, a smaller avalanche or cornice fall could trigger one of these monster slides, or a backcountry traveler could get unlucky and cross a trigger point where the snowpack is thinner, initiating a very dangerous avalanche (<strong><a href="https://www.youtube.com/watch?v=PyHc_9gjFWA">video</a></strong>).</p&gt;

<p>The weekend’s storm created the potential for avalanches within the new and wind-drifted snow. Yesterday at Buck Ridge, Alex saw a natural slide that failed around 18” deep and noted that these avalanches, while small compared to those breaking deeply on persistent weak layers, are large enough to bury or injure a rider or skier (<a href="https://www.youtube.com/watch?v=LlLu6b2UzU8"><strong><span>video</span>…;). Terrain features of concern include slopes below or adjacent to cornices, areas with pillows of drifted snow or with a textured snow surface, and slopes with signs of instability such as cracking.</p>

<p><span>If you choose to play in avalanche terrain, identify and avoid wind-loaded slopes. Select low-consequence terrain (smaller, less steep pitches without terrain traps), and follow safe travel practices by carrying rescue gear and traveling one at a time in avalanche-exposed areas while a partner watches from a safe spot. The danger is rated MODERATE. </span></p>

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Poor Test Scores near Ross Peak

Date
Activity
Skiing

From IG Message: ECTP20 on a NE facing slope on Ross Peak at 8700' elevation.

Region
Bridger Range
Location (from list)
Ross Peak
Observer Name
Connor Koch

Small Avalanches on Test Slopes, Buck Ridge

Buck Ridge
Northern Madison
Code
SS-ACc
Latitude
45.17190
Longitude
-111.38000
Notes

From obs: "On a small test slope near Muddy Creek we intentionally triggered several small avalanches in wind loaded terrain." 

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Cornice fall triggered by human or explosive action
Trigger Modifier
c-A controlled or intentional release by the indicated trigger
Problem Type
Wind-Drifted Snow
Snow Observation Source
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Natural Avalanches near Buck Ridge

Buck Ridge
Northern Madison
Code
SS-N-R1-D1
Aspect
E
Latitude
45.17190
Longitude
-111.38000
Notes

From obs: "Behind McAtee Basin, we saw a small natural wind slab avalanche on an east facing slope, and we saw a natural wind slab in Bear Creek." 

Number of slides
2
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
1
D size
1
Problem Type
Wind-Drifted Snow
Snow Observation Source
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

On a small test slope near Muddy Creek we intentionally triggered several small avalanches in wind-loaded terrain by knocking chunks of cornice off. Photo: GNFAC

Northern Madison, 2024-03-24