24-25

Wind/storm slab avalanche in the Bridger Range

Ross Peak
Bridger Range
Code
SS-ASc-R2-D2-I
Elevation
8300
Aspect
NE
Latitude
45.85860
Longitude
-110.95600
Notes

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. 

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Skier
Trigger Modifier
c-A controlled or intentional release by the indicated trigger
R size
2
D size
2
Bed Surface
I - Interface between new and old snow
Problem Type
Wind-Drifted Snow
Slab Thickness
24.0 inches
Slab Width
20.00ft
Snow Observation Source
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

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