24-25

Propagation in ECTs, Rob's Knob

Date
Activity
Skiing

Snow surface soft with ~3" of new, mod-strong SW winds at 11am 

Reactive tests in snowpits with low to moderate ECTP scores.  HS 105, NE aspects at 9480'.  

Experienced collapsing on the north end of Rob's, likely failing on buried surface hoar that was evident in pit.  

Region
Cooke City
Location (from list)
Fisher Mtn.
Observer Name
BMG L1

Collapsing / Poor stability test scores, West Henderson

Date
Activity
Skiing

We toured above 9000' on a W to SW aspects on Henderson Mtn.  We experienced several collapses and had propagation in multiple ECTs performed.  HS varies between 85-105cm.  Snowpilot pit is from 9820' W aspect, photo from 9940': both with ECTP results.  

Snow surface variable with wind boards and radiation crusts, mixed with soft snow in shaded aspects.  

Region
Cooke City
Location (from list)
Daisy Pass
Observer Name
BMG L1

GNFAC Avalanche Forecast for Sun Dec 22, 2024

Snowpack and Avalanche Discussion

<p><span><span><span><span><span><span>Today a person can trigger large </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>that break on weak layers buried in the middle of the snowpack or near the ground. These persistent slab avalanches have become less likely since snowfall and strong winds ended late Wednesday, but the potential size and consequences remain large.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>During the first half of this week strong winds drifted new snow into thick, heavy slabs (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=w-aXzlPHrYA"><span><span><span><strong>… video</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). On Wednesday there were multiple large natural avalanches near Cooke City (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=zCdhitUHk1o"><span><span><span><strong>…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/24/large-persistent-slab-avalanche-h… photo</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/24/persistent-slab-avalanche-fisher"… photo</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>), and an avalanche on Saddle Peak broke 1-3 feet deep (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/32548"><span><span><span><strong><span…;). On Tuesday Ian triggered an avalanche remotely (from lower angle terrain nearby) on Buck Ridge near Big Sky (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/32497"><span><span><span><strong><span…;), and on Friday a skier had a large collapse in the Bridger Range (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/32582"><span><span><span><strong><span…;).&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Choose small, simple, non-wind-loaded slopes with clean runouts free of hazards like rocks, trees or cliffs. If you have any doubts about snowpack stability avoid slopes steeper than 30 degrees and be cautious of runout zones below.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Yesterday on Buck Ridge a snowmobiler triggered a 12” deep</span></span></span></span></span></span><span><span><span><strong><span><span> </span></span></strong></span></span></span><span><span><span><span><span><span>wind slab avalanche (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/32601"><span><span><span><strong><span…;). Strong winds last night might have formed fresh </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>, and a few potentially unstable drifts could remain from earlier in the week. Look for signs of wind-drifted snow and be cautious of wind-loaded slopes, especially where consequences of a slide are higher due to terrain traps.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Carefully and continuously assess the snowpack and terrain for avalanche potential, and travel one person at a time on steep slopes or through runouts. The avalanche danger is MODERATE.</span></span></span></span></span></span></p>

Upcoming Avalanche Education and Events

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Snowmobiler triggered wind slab on Buck Ridge

Buck Ridge
Northern Madison
Code
SS-AM-R2-D1.5
Elevation
9500
Aspect
NE
Latitude
45.17190
Longitude
-111.38000
Notes

From email: "Rode buck today.  It was very windy this week.  Open areas are quite scoured, but there are still great stashes to be found if you hunt around.  We triggered a 12" soft wind slab on a NE facing slope at 9.5k'." 

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Snowmobile
R size
2
D size
1.5
Problem Type
Wind Slab
Slab Thickness
12.0 inches
Vertical Fall
50ft
Slab Width
100.00ft
Snow Observation Source
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Blue Creek snowpack

Date
Activity
Snowmobiling

ECTP 15 75cm up from ground. HS90-110 9000ft SE aspect. Down 1000 feet similar aspect we also got propagation up 23cm with a HS of 55cm. Photo from the 9000ft pit.

Region
Island Park
Location (from list)
CENTENNIAL RANGE
Observer Name
zach bailey

Soft slabs on Buck

Date
Activity
Snowmobiling

From email: "Rode buck today.  It was very windy this week.  Open areas are quite scoured, but there are still great stashes to be found if you hunt around.  We triggered a 12" soft wind slab on a NE facing slope at 9,5k'." 

Region
Northern Madison
Location (from list)
Buck Ridge
Observer Name
Julian Gerardi

Warm at the Maid

Date
Activity
Skiing

We got into the Maid basin around 9:30 am while things were still cold. Much evidence of the recent wind event in the alpine with widespread wind slabs ranging in thickness from an inch to feet. There was some natural avalanche activity on the peak south of mt Bole. 
 

Got an ECTN 19 and 23 on a SE aspect at 9300’ HS 95cm

This was on a thin layer of facets sitting under a crust at 58cm. With a few prior hand pits showing planar shear on this layer we opted to keep it low angle.

By noon things were getting quite warm and Skiing through the thinly covered, glopy bushwhack back to the trail was our crux for the day. 

Region
Northern Gallatin
Location (from list)
Maid of the Mist