24-25

Skier triggered wind slabs and wet loose

Date
Activity
Skiing
Snowmobiling

Today A Skier triggered a 6”x20’ wide wind slab on a N aspect at 9,800’.

Skiers triggered D1-D1.5 wet loose on SE aspect at 10,000’.

There were also natural small wet loose slides today and yesterday. Long running, but narrow, in steep terrain. Typically initiated near rock outcrops.

Today was hotter than yesterday and the top of the snowpack got pretty wet before clouds built in the afternoon. Snow stayed dry on due north up high. 

 

Region
Cooke City
Location (from list)
COOKE CITY
Observer Name
Alex Marienthal

Variable Surface Conditions

Date
Activity
Skiing

We rode into Fairy Lake and climbed up to the Great One. Surface conditions ranged from gloppy, wet snow to firm, dry wind slabs with very little powder in between. There had been a fair amount of wind-slab and wet loose avalanche activity in the area over the weekend, but things were quite today. We had a report of a human-triggered wind slab avalanche in the Great One on Saturday. 

By 11:00 AM a layer of high clouds moved overhead and limited the melt-down input from the sun. Ambient temperatures reaching 50 degrees F didn't do the snow quality any favors at mid and low elevations but additionally didn't result in any natural wet snow avalanches that I saw. 

Wind-slabs were relatively thin (a couple inches to 8" thick). We did get cracking in a few drifts that was limited to the area directly influenced by our skis. We dug at the top of the Great One with unremarkable results and proceeded down the run. 

Tomorrow looks to be cooler with limited snow accumulation. If this forecast pans out, triggering an avalanche will be unlikely. Let's hope for more snow than is in the forecast!

Region
Bridger Range
Location (from list)
Fairy Lake
Observer Name
Dave Zinn

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No Region, 2025-04-07

GNFAC Avalanche Forecast for Mon Apr 7, 2025

Snowpack and Avalanche Discussion

<p>This morning, avalanche conditions are generally safe, and slides are unlikely. Warming during the day will unlock snow surfaces and make <strong>wet loose </strong>and <strong>wind slab avalanches</strong> possible. Thankfully, both of these problems will result in relatively small avalanches and are avoidable by timing your day thoughtfully and identifying key terrain features.</p>

<p>Increasing cloud cover and winds may keep snow surfaces cooler than yesterday and multiple days of subsequent freezing and thawing temperatures took the edge off the wet snow danger. However, as the sun and above-freezing temperatures melt snow surfaces, <strong>wet loose avalanches</strong> may occur naturally or with human triggers. Last week’s snow sits above firm crusts, a bed surface that can result in long-running slides. Move to lower-angle terrain or colder, drier slopes on northern aspects when the top few inches of snow become wet or roller balls signal deteriorating stability. Stability will be best first thing in the morning and progressively worsen on slopes in direct sun.</p>

<p>Snow surfaces are hardening, and <strong>wind slab avalanches</strong> are becoming less likely as time separates us from the most recent snowfall and wind loading events. Slabs of drifted snow often present as textured, stiff or rounded snow surfaces. The most likely location for this problem is immediately below corniced ridgelines and in upper elevation gullies holding dry snow. Either avoid these isolated locations or evaluate drifted slopes for instability. While these wind slabs are relatively small, they can push skiers and riders into rocks and off cliffs in steep terrain.</p>

<p>A related concern is <strong>cornice fall</strong>. These overhanging masses of snow near ridgelines are enormous and can break unpredictably far from the edge, especially during spring warm-ups. Minimize your time on slopes below cornices and stay far from the edge while travelling above them.</p>

<p><strong>Recent Avalanche Activity: </strong>Yesterday, skiers south of Cooke City noted a pair of relatively small wet loose avalanches (<a href="https://www.mtavalanche.com/node/34867"><strong><span>details</span></s…;). On Saturday in the Bridger Range, skiers triggered wind slab avalanches on Saddle Peak and The Great One; some loose snow avalanches occurred naturally (<a href="https://www.mtavalanche.com/node/34844"><strong><span>Saddle Peak</span></strong></a>, <a href="https://www.mtavalanche.com/node/34845"><strong><span>The Great One</span></strong></a>, <a href="https://www.mtavalanche.com/images/25/natural-loose-slides-bridge-ridge…;), and in Cooke City, wind drifts breaking up to 8 inches deep were more reactive than anticipated (<a href="https://www.mtavalanche.com/node/34848"><strong><span>observation and video</span></strong></a>).</p>

<p><span>The avalanche danger is LOW this morning and will rise to MODERATE as surface crusts break down. </span></p>

Hyalite Road Closure

The Hyalite Canyon Road is closed to ALL MOTORIZED VEHICLES until May 16. This is a regular annual road closure to reduce road damage during the spring thaw. Bicycle and foot traffic are allowed. Contact the Bozeman FS Ranger District for more info.

Wet Loose Avalanches Cooke City

Hayden Creek
Cooke City
Code
WL-NC-R1-D1-S
Elevation
10000
Aspect
E
Latitude
44.99520
Longitude
-109.90800
Notes

While touring south of town today, we observed two D1 wet loose avalanches on an east aspect at 10000’. Both occurred at 11am and were triggered by a small cornice fall due to rapid warming.

Number of slides
2
Number caught
0
Number buried
0
Avalanche Type
Wet loose-snow avalanche
Trigger
Cornice fall
R size
1
D size
1
Bed Surface
S - Avalanche released within new snow
Problem Type
Loose Wet
Snow Observation Source
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

Wet Loose Avalanches Cooke City

Date
Activity
Skiing

While touring south of town today, we observed two D1 wet loose avalanches on an east aspect at 10000’. Both occurred at 11am and were triggered by a small cornice fall due to rapid warming.

Region
Cooke City
Location (from list)
Hayden Creek
Observer Name
Nina Hance