22-23

Small natural wind slab near Cooke City

COOKE CITY
Cooke City
Code
N-R1-D2
Elevation
10000
Aspect
SW
Latitude
45.02020
Longitude
-109.93800
Notes

2/10/23: Our group did a big loop - Daisy- wolverine- goose - sheep -lulu. Saw minimal wind transport except on high points ( see photo). After looking all day saw an R1D2 slide (see 2nd photo) on a ENE slope above 10,000' south of Lulu pass, unknown trigger, though the whole area around the slide had cornice growth. We observed a lot of tracks highmarking into windloaded alpine slopes but saw no rider triggered avalanches. 

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

2/10/23: "After looking all day saw an R1D2 slide (see 2nd photo) on a ENE slope above 10,000' south of Lulu pass, unknown trigger, though the whole area around the slide had cornice growth. We observed a lot of tracks highmarking into windloaded alpine slopes but saw no rider triggered avalanches." Photo: S. Regan

Cooke City, 2023-02-12

Wind slabs over a weak layer

Date
Activity
Skiing

We skied up the Throne and encountered serious wind effected terrain. Some slopes were blown clear, others has ripples of sastrugi, and yet others were wind-loaded. After a pit down low yielded nothing significant, we skied higher to look for wind-loaded slopes. We found a natural crack that occurred in a wind slab, and then we dug near the ridge at a spot we typically descend. We got an ECTP9, an unstable test result. The video shows it well. Wind loads are isolated, but they could avalanche. They are easy to find: they were the only smooth parts of the slope.

Region
Bridger Range
Location (from list)
The Throne
Observer Name
Doug Chabot

GNFAC Avalanche Forecast for Sun Feb 12, 2023

Snowpack and Avalanche Discussion

<p><span><span><span><span><span><span>Human-triggered avalanches are possible in the mountains near Cooke City, Bozeman and Big Sky. Early last week these mountains received 8-14” of new snow. Moderate to strong westerly winds drifted the new snow into heavier slabs which added weight to weak layers buried 3-4 feet deep and near the bottom of the snowpack (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=9uVGnUshKhY"><span><span><span><strong>… video</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>, </span></span></span></span></span></span><a href="https://youtu.be/XTrscbqcELU"><span><span><span><strong><span><u><span>… Ridge video</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). Recent drifts have become more stable since they formed 2-3 days ago, but are still a concern where they formed on slopes with buried weak layers. Steep slopes that were wind-loaded over the last week are the most dangerous and should be the first ruled out of your travel plan. If you choose to ride any steep slope, first dig down to look for and test buried weak layers. If you get propagating results in an Extended Column Test, find lower angle slopes.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Warm temperatures and sunshine will cause the snow surface to become wet, and may create a few small loose snow slides or cause cornices to become unstable along ridgelines. Yesterday on Mt. Blackmore in Hyalite skiers had a cornice crack near their feet and break away from the ridgeline (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28099"><span><span><span><strong><span…;). Today avalanches are possible and avalanche danger is MODERATE.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Near West Yellowstone and in the southern Madison and southern Gallatin Ranges avalanches are unlikely. The snowpack has had sufficient time to gain strength since two weeks ago when a large storm caused many natural avalanches (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/27937"><span><span><span><strong><span…. 31 observation</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). This trend towards better stability is supported by relatively few avalanches over the last two weeks, buried weak layers becoming less reactive in stability tests, and only a few small storms adding minimal weight (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=a-QVCM1CUWs&amp;list=PLXu5151nmAvTi1DBS… video</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). A small avalanche was triggered by a snowmobiler last Thursday near Tepee Basin (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28079"><span><span><span><strong><span…;), and the last avalanche prior to that was twelve days ago near Lionhead (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/27941"><span><span><span><strong><span… triggered wind slab</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>).&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Today, travel on or across steep slopes is generally safe. Most slopes are stable, but as long as there is snow on the ground the chance of an avalanche is never zero. While the odds are in your favor, you can further improve your chances by following safe travel protocols and carefully assessing the snowpack. Before riding or skiing steep slopes dig down 3-4 feet to look for and test buried weak layers (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=EBK444Tjh9I"><span><span><span><strong>… Fork video</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). Carry proper avalanche rescue gear and allow no more than one person at a time on steep slopes. The avalanche danger is LOW.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Please share avalanche, snowpack or weather observations via our</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/add/snow_obs"><span><span><span><span>…; </span></span></span></span></span></span><span><span><span><strong><span><u><span><span>website</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>, email (</span></span></span></span></span></span><span><span><span><strong><span><span>mtavalanche@gmail.com</span></span></strong></span></span></span><span><span><span><span><span><span>), phone (406-587-6984), or Instagram (#gnfacobs).</span></span></span></span></span></span></p>

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Cornice crack triggered by skiers

Mt Blackmore
Northern Gallatin
Code
C-ASu
Elevation
9600
Aspect
NE
Latitude
45.44340
Longitude
-110.99700
Notes

Also of note, as we traversed a corniced ridge later in the day, two of our group members simultaneously came too close to the edge of a cornice and it broke away, but did not fall down the slope. Fortunately, everyone was alright, but it was a close call and we will definitely be more mindful next time. We believe the cornice was made more sensitive by the warm weather over the past few days. 

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Cornice fall
Trigger
Skier
Trigger Modifier
u-An unintentional release
Problem Type
Wind-Drifted Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

From obs. 2/11/23: "...Also of note, as we traversed a corniced ridge later in the day, two of our group members simultaneously came too close to the edge of a cornice and it broke away, but did not fall down the slope. Fortunately, everyone was alright, but it was a close call..." Photo: E. Heiman

Northern Gallatin, 2023-02-12