23-24

Unstable Snow in Cooke City

Date
Activity
Snowmobiling

We rode to the bottom of an avalanche on Sheep Mountain that had been triggered by riders from the bottom. This avalanche happened on Monday, 01/14, but by today it had been filled in by recent winds and new snow. From here we worked our way north of Round Lake and found 10"-12" of new snow (0.5" SWE), compared to the 5" of new snow near Sheep Mountain. Near the wilderness boundary, we found unstable snow and while getting a snowmobile unstuck in the flats remotely triggered a small avalanche from 100' away. We then rode to a northern aspect at 9600' and found 170 cm of snow and had poor results in our stability tests, with an ECTP 6 on buried weak layers below the last week and a half of storms. 
 

From here we rode to the top of Henderson Bench and dug on an east-facing slope at 9500'. While walking to our snowpit location we collapsed the slope and a small pocket of snow below a tree avalanched. Here we again had poor stability test results, ECTP 11, this area had previously been wind-loaded during last week's storm. Storm totals here were less than what we found north of Round Lake, with 5" of new snow at 3 pm (0.2" of SWE). 

Wind through the day was calm but is expected to increase tonight. Snow will continue tonight into tomorrow morning. Expect danger to rise as snow totals increase and wind begins transporting snow. 
 

Region
Cooke City
Location (from list)
Sheep Mountain
Observer Name
Zach Peterson

Multiple Remotely Triggered Avalanches, N. of Cooke City

COOKE CITY
Cooke City
Code
SS-AMr
Latitude
45.02020
Longitude
-109.93800
Notes

We receive vague reports of a group reporting multiple remotely triggered avalanches north of Cooke City on 1/16. A member of this same group similarly triggered an avalanche on Sheep Mountain on 1/14 (video overview attached to the entry), so the reports of avalanches yesterday are likely reliable. 

Number of slides
3
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Snowmobile
Trigger Modifier
r-A remote avalanche released by the indicated trigger
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

GNFAC Avalanche Forecast for Wed Jan 17, 2024

Snowpack and Avalanche Discussion

<p>New and wind-drifted snow will load persistent weak layers buried throughout the mountains near Cooke City, West Yellowstone, and Island Park, making avalanche conditions more dangerous. Human-triggered avalanches are likely. Slides will break 1-2 feet deep, be large enough to bury or injure backcountry travelers, and may be triggered from on or near steep slopes.</p>

<p>Yesterday, Doug and Ian rode at Lionhead, triggering collapses and shooting cracks, noting “heads up” conditions and recommending travelers avoid crossing the lower portions of avalanche paths (runout zones) once it begins snowing (<a href="https://www.youtube.com/watch?v=MRJIwLgWH0M"><strong><span>video</span>…;). In Cooke City on Sunday, a rider triggered an avalanche that barely missed him as he crossed below a steep slope on Sheep Mountain (<a href="https://youtu.be/0ZQ3asjNobg"><strong><span>video</span></strong></a&gt;). On Monday in Lionhead, a group triggered an avalanche from twenty feet away (<a href="https://www.mtavalanche.com/node/29951"><strong><span>photos and details</span></strong></a>). Others saw widespread collapsing and cracking that shot 200 feet from their sleds <span>(</span><a href="https://www.mtavalanche.com/node/29961"><strong><span>observation</span…;, </span><a href="https://www.mtavalanche.com/node/29964"><strong><span>observation 2</span></strong></a><span>).</span> Watch this <a href="https://www.youtube.com/watch?v=Fb3C0IneUP8"><strong><span>video</span>…; from Lionhead at minute 10:30 for a remarkable example of the shooting cracks. <span>A skier south of Cooke City noted many collapses, but one on a low-angle slope shot cracks out 100 feet that then “circled back in a big loop! It was a 3-second symphony of movement in the snow”</span> (<a href="https://www.mtavalanche.com/node/29956"><strong><span>photos and details</span></strong></a>). Equate these observations from Cooke City and Lionhead to Island Park and the Southern Gallatin and Southern Madison Ranges, where the snowpack and recent loading patterns are similar (<a href="https://www.youtube.com/watch?v=aTnE5gzG1sc"><strong><span>Taylor Fork video</span></strong></a>, <a href="https://youtu.be/_Q_YPhkGuQk"><strong><span>Centennials video</span></strong></a>).</p>

<p>Human-triggered avalanches will become more likely as snow falls today. Safely avoid avalanches by traveling on slopes less than 30 degrees without steep terrain above. Careful route-finding, snowpack assessment, and conservative decision-making are essential for travel on and around steeper slopes. The danger is rated CONSIDERABLE.</p>

<p>Human-triggered avalanches are possible in the mountains around Bozeman and Big Sky. They are most likely on slopes recently loaded with wind-drifted snow or where cohesive slabs rest on persistent weak layers (<a href="https://youtu.be/UU09uX5hvGY"><strong><span>Beehive video</span></strong></a>, <a href="https://youtu.be/tj7d4Y8X5ms"><strong><span>Blackmore video</span></strong></a>). An <a href="https://www.mtavalanche.com/node/29986"><strong><span>observation and photos</span></strong></a><strong> </strong>of two natural avalanches near Divide Peak highlight the concern about wind-loaded slopes. Seek wind-sheltered terrain and assess the snowpack before traveling on slopes steeper than 30 degrees.</p>

<p>Watch for signs of increasing instability as today’s storm progresses. These could include natural avalanches, shooting cracks or collapsing. If observed, avoid avalanche terrain.</p>

<p>The danger is rated MODERATE but will rise to CONSIDERABLE if daytime snow totals exceed forecast amounts.</p>

Upcoming Avalanche Education and Events

Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.

Every weekend in Cooke City: Friday at The Antlers at 7 p.m., Free Avalanche Awareness and Current Conditions talk, and Saturday from 10 a.m.-2 p.m. at Round Lake Warming Hut, Free Rescue Practice.

Divide Pk Wind loading

Date
Activity
Snowboarding

On my tour up the main fork of Hyalite today I noticed two slides near Divide Peak caused by wind loading.  There was a wind skim on all snow surfaces in the Basin and I experiences a bit of collapsing while walking across the basin in the flats on small wind loaded pockets

Region
Northern Gallatin
Location (from list)
Divide Peak

Small Wind Slab Avalanche, Buck Ridge

Buck Ridge
Northern Madison
Code
SS-R2-D1
Latitude
45.17190
Longitude
-111.38000
Notes

Riders saw a small wind slab avalanche in the Beaver Creek area of Buck Ridge

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

Skiing west face Woody

Date
Activity
Skiing

We skied a 25 degree west slope today on Woody Ridge.  No sign of instability.  No wumphing or cracking.  No wind effected snow, in forest

5 degrees,at 100pm, light breeze.

HS 110-115 cm

new snow 30 cm. fairly cohesive but not bonded to old-variable

Layer of facets below new snow and above hard layer 60cm deep

Hard layer 10-15cm thick

facets below hard layer

The snowpack depth was variable.  New snow not well bonded to old snow in places

we climbed to 9550 and stopped as terrain got steeper

Coverage was good.  Very good skiing

I might add that several times during the day we commented on the difference in red flags we experienced from Beau's report the day before. We were both S. of Cooke, but differences in that we were in wind-protected forest most of the day, although in meadows above about 9K, more importantly, perhaps is aspect - we were W. and I think from photos, Beau was on an E. aspect. Although we didn't get collapsing or shooting cracks, we all recognized the poor snow structure we were on and we pulled skins when slope angle approached 30 deg.

Average snow depth was only in the 110 cm range and the terrain we were in looked very different from that in a year with a normal snowpack. Sill some snow-snakes and staubs concealed barely below the surface.

Region
Cooke City
Location (from list)
Woody Ridge
Observer Name
Jesse Logan. Traute Parrie. Don Carroll

January 16 Observations

Date
Activity
Skiing

From email: "We skied a 25 degree west slope today on Woody Ridge.  No sign of instability.  No wumphing or cracking.  We all recognized the poor snow structure we were on and we pulled skins when the slope angle approached 30 deg. 5 degrees, at 100pm, light breeze.

HS 110-115 cm

new snow 30 cm. fairly cohesive but not bonded to old-variable

Layer of facets below new snow and above hard layer 60cm deep

Hard layer 10-15cm thick

facets below hard layer

The snowpack depth was variable.  New snow not well bonded to old snow in places we climbed to 9550 and stopped as terrain got steeper"

 

Region
Cooke City
Location (from list)
Republic Creek
Observer Name
Don Carroll