24-25

Natural Avalanche on the Fin

Republic Mountain
Cooke City
Code
SS-N-R2-D2
Elevation
9800
Aspect
E
Latitude
45.00500
Longitude
-109.95700
Notes

The clouds broke briefly around noon today in Cooke City. It looks like the Fin slide naturally in the past day or so (12/15 or 12/16). It looks like two sections of the face slid, one from the top, and one lower and to the right in the photo. 

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

GNFAC Avalanche Forecast for Wed Dec 18, 2024

Snowpack and Avalanche Discussion

<p>Dangerous avalanche conditions exist across the advisory area. New and wind-drifted snow are adding weight to persistent weak layers buried 1-2.5 feet deep. The mountains have received snow for the last four days straight, with 1-2” in the last 24 hours. Today, strong winds gusting to 60 mph will transport recent snow, thicken slabs over weak layers, and build unstable drifts at all elevations.</p>

<p><strong>Four-Day Storm Totals: </strong></p>

<ul>
<li>Bridger Range, Cooke City, Island Park and Big Sky - 15-23” (1.4-2.1” SWE)</li>
<li>West Yellowstone, Taylor Fork and Hyalite Canyon - 9-14” (0.8-1.4” SWE)</li>
</ul>

<p>The threat of <strong>persistent slab avalanches</strong> is our primary concern, with human-triggered slides likely on steep slopes. Yesterday, Ian and his partners triggered an avalanche on a steep slope while they were still 200 feet away at Buck Ridge (<a href="https://www.mtavalanche.com/node/32490"><strong><span>details and media</span></strong></a>). In the Centennial Range, Mark traveled “really carefully, avoiding avalanche terrain” because of a weak layer of facets buried 1-2 feet deep throughout the range (<a href="https://www.youtube.com/watch?v=4xSA_C9cPuc"><strong><span>video</span>…;), and in Cooke City, I triggered <em>whumphing </em>collapses (<a href="https://www.youtube.com/watch?v=hf4zYmfj_6E"><strong><span>video</span>…;). Recent avalanches, whumphs, and shooting cracks communicate instability. Heed the message and minimize your exposure to steep terrain.</p>

<p><strong>Wind slab avalanches </strong>failing 1-3 feet deep are likely. Their distribution will be widespread and atypical as strong winds rip through recent snow. Yesterday, we saw clear examples of wind-loaded terrain near Cooke City with large drifts at ridgelines and gullies. Similar images can be found across the advisory area (<a href="https://www.mtavalanche.com/images/24/cross-loading-henderson-mountain"…; </strong><a href="https://www.mtavalanche.com/images/24/cross-loading-miller-ridge"><stro… 2</span></strong></a>). Beyond recent avalanche activity, shooting cracks and a stiffening of the snow surface indicate unstable wind slabs.</p>

<p><strong>Notable Recent Avalanche Activity Since Sunday </strong>(More at <a href="https://www.mtavalanche.com/avalanche-activity"><strong><span>Avalanche log</span></strong></a>)<strong>: </strong></p>

<ul>
<li>A remotely triggered avalanche at Buck Ridge slid on a steep slope 200 feet away from a group of riders (<a href="https://www.mtavalanche.com/node/32430"><strong><span>details and photos</span></strong></a>)</li>
<li>Two recent avalanches in McAtee Basin (<a href="https://www.mtavalanche.com/node/32498"><strong><span>details and photos</span></strong></a>)</li>
<li>An intentionally triggered slide that broke up to 2 feet deep near Ross Peak in the Bridger Range (<a href="https://www.mtavalanche.com/node/32487"><strong><span>details and photo</span></strong></a>)</li>
<li>Many natural avalanches on Saddle Peak and in Argentina Bowl (<a href="https://www.mtavalanche.com/node/32464"><strong><span>details</span></s…;)</li>
<li>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 video and ob</span></strong></a>)</li>
<li>Small snowmobiler-triggered avalanche at Buck Ridge (<a href="https://www.mtavalanche.com/node/32513"><strong><span>details and photo</span></strong></a>)</li>
<li>Persistent slab avalanche near Island Park (<a href="https://www.mtavalanche.com/node/32422"><strong><span>details</span></s…;)</li>
<li>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…;)</li>
<li>Skier triggered storm slab avalanche on The Throne (<a href="https://www.mtavalanche.com/node/32444"><strong><span>details</span></s…;)</li>
</ul>

<p>Today, seek out smaller, lower-consequence terrain and slopes sheltered from the effects of the wind. Recreating in terrain less than 30 degrees without steeper terrain above largely eliminates the risk of avalanches. Safer travel in and around avalanche terrain requires careful route-finding and snowpack assessment. The avalanche danger is rated CONSIDERABLE.</p>

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Collapsing on West Henderson

Henderson Mountain
Cooke City
Code
Elevation
10000
Aspect
SW
Latitude
45.04700
Longitude
-109.94000
Notes

As we entered non wind-effected, upper-elevation terrain on Henderson, we consistently triggered many localized collapses and heard audible whumpfs. 

Number of slides
0
Number caught
0
Number buried
0
Problem Type
Persistent Slab
Snow Observation Source
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Red Flag
Advisory Year

Snowmobile triggered avalanche, Buck Ridge

Buck Ridge
Northern Madison
Code
SS-AMu-R2-D1-O
Aspect
NE
Latitude
45.17190
Longitude
-111.38000
Notes

From FB messenger: “Bottom of Slats area. Buck ridge. 
NE slope/hole wind loaded. Sled triggered, 315 pm Sunday Dec 15, 2024”

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Snowmobile
Trigger Modifier
u-An unintentional release
R size
2
D size
1
Bed Surface
O - Old snow
Problem Type
Wind Slab
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Snowmobile triggered avalanche, Buck Ridge

Date
Activity
Snowmobiling

From FB messenger: “Bottom of Slats area. Buck ridge. 
NE slope/hole wind loaded. Sled triggered, 315 pm Sunday Dec 15, 2024”

Region
Northern Madison
Location (from list)
Buck Ridge