24-25

Snowmobile Triggered Avalanche-Cooke City

Date
Activity
Skiing

Observed a snowmobile triggered avalanche today. East facing slope, approx 9700', between Fischer Peak and LuLu pass. Rider was not caught. HS-AMu-D1-R1-I. Observed lots of wind transport and loading from strong w/sw winds today. 

Region
Cooke City
Location (from list)
Lulu Pass
Observer Name
Nick Gaddy

Test score, sky cover, and ski conditions at the Bacon Rind

Date
Activity
Skiing
Snowboarding

8761ft

43 NE

13 degree slope

HST 125

ECTP 12 50 down

 

Soft snow ski pen 30 cm

supportable pow

clear skis tell 11:20

11:20 few

Region
Southern Madison
Location (from list)
Bacon Rind
Observer Name
Tagg Cole

Wet Slides on Ice Climb Approaches

Date
Activity
Ice Climbing

Up at G2 on Sunday (2/23) small wet sloughs were coming down to the left & right of the climb all day. A couple bigger wet slides had totally taken out sections of the bootpack approach from G2 to Hangover. Saw big pinwheels and sticky snow all day. Most stuff available to slough probably fell already but stay alert up there.

Region
Northern Gallatin
Location (from list)
Hyalite - main fork
Observer Name
BP

Warm up, signs of instability Pioneer Scenic Byway

Date
Activity
Snowmobiling

Rode around the pioneer scenic byway with the motorized avalanche fundamentals course. 

At 8500 SW aspect there was 120cm snow ( see picture for structure) ECTP17, ECTP23 failing on large basal facets/ depth hoar 25cm up from the ground. New snow from February is 1/2 the HS. 

As the afternoon warmed up we saw roller ball, small loose wet avalanches and shooting cracking from snowmobile tracks. At the end of the day we observed a very small avalanche on a road cut, also shooting from a track. 

We did not ride much off trail, where we riding the snowpack was shallow and you could easily punch into the weak snow. 

Region
Dillon Area
Location (from list)
East Pioneer Mountains
Observer Name
S Regan

GNFAC Avalanche Forecast for Mon Feb 24, 2025

Snowpack and Avalanche Discussion

<p><span><span><span><span><span><span>Heavy new snow and strong wind make human-triggered avalanches likely where the snow is drifted into stiffer slabs. </span></span></span></span></span></span><span><span><span><strong><span><span>Wind slab avalanches</span></span></strong></span></span></span><span><span><span><span><span><span> are the primary concern. These will be easy to trigger and could break 1-2 feet deep. Yesterday I was in Republic Creek and found fresh drifts that broke easily (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34343"><span><span><span><span><span><… and photos</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>). </span></span></span></span></span></span><span><span><span><strong><span><span>Storm slab avalanches</span></span></strong></span></span></span><span><span><span><span><span><span> are possible where the snow is not drifted. Watch for cracking around your skis or sled as a sign the new snow could slide on steeper slopes.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>We heard of an avalanche triggered by a snowmobiler east of Mt. Abundance on Saturday which broke 2 feet deep, 250’ wide, and was triggered from flat terrain above the slope (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34344"><span><span><span><span><span><…;). It possibly failed on a thin weak layer buried earlier in February (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/republic-creek-pit-west-aspect-97…;). This type of persistent slab instability is not widespread around Cooke City, but with the added weight of today’s snow there might be a couple slopes where an avalanche could break 2-3’ deep and hundreds of feet wide. </span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Be cautious of slopes steeper than 30 degrees and steer clear of fresh drifts. </span></span></span></span></span></span><span><span><span><span><span><span>The avalanche danger is CONSIDERABLE on wind-loaded slopes and MODERATE on other slopes.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Near West Yellowstone and the southern Madison and southern Gallatin ranges a person can trigger large avalanches that break on weak layers buried 1-3 feet deep. These </span></span></span></span></span></span><span><span><span><strong><span><span>persistent slab avalanches</span></span></strong></span></span></span><span><span><span><span><span><span> are tricky as they might be triggered by the first person, or after multiple people have ridden a slope, and not every slope has this instability. Yesterday Mark and Dave went to Tepee Basin to look at a slide that partially buried a rider on Friday (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34336"><span><span><span><span><span><…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34301"><span><span><span><span><span><… and photos</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>). Watch their </span></span></span></span></span></span><a href="https://youtu.be/jdtQgYx3MNA?feature=shared"><span><span><span><span><s…; for insight into this problem and some key takeaways from the group involved. Keep in mind, you aren't good to go by just avoiding the steep, upper-elevation, wind-loaded bowls. Steep slopes at mid-elevations harbor weak snow and have the potential for an avalanche.</span></span></span></span></span></span></p>

<p><span><span><span><strong><span><span>Wind slab avalanches</span></span></strong></span></span></span><span><span><span><span><span><span> will be easy to trigger where today’s snow is drifted into fresh slabs. These might not be very big, but can easily knock you over or carry you down a slope. Be cautious of wind-loaded slopes, especially where a slide could carry you into trees, rocks or over cliffs. </span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Human-triggered avalanches are possible and avalanche danger is MODERATE.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Across the rest of the forecast area </span></span></span></span></span></span><span><span><span><strong><span><span>wind slab avalanches </span></span></strong></span></span></span><span><span><span><span><span><span>can be triggered where strong wind has drifted snow into stiff slabs. Fresh drifts will be easy to trigger, but relatively small, and are most hazardous in terrain with larger consequences such as thick trees or cliffs. Also be cautious of older drifts from earlier in the week (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/wind-slab-hardscrabble"><span><sp…;), although most of these should be unreactive by now.</span></span></span></span></span></span></p>

<p><span><span><span><strong><span><span>Wet loose avalanches</span></span></strong></span></span></span><span><span><span><span><span><span> are possible due to above freezing temperatures, but cloudy skies and wind should minimize this problem today. Be careful of steep slopes if you find a wet or sticky snow surface.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Steer clear of steep slopes with fresh drifts or a wet snow surface, especially if a slide could push you into trees, over a cliff or pile up deeper in a confined gully. Human-triggered avalanches are possible and the avalanche danger is MODERATE.</span></span></span></span></span></span></p>

<h3><span><span><span><strong><span><span>Special Note - Roof avalanches</span></span></strong></span></span></span></h3>

<p><span><span><span><span><span><span>Many roofs have lots of snow on them that may come crashing down as a roof avalanche during the warm temperatures. Avalanche fatalities from roof avalanches are not uncommon. Kids are especially vulnerable because they often play near houses while no one is watching.</span></span></span></span></span></span></p>

Upcoming Avalanche Education and Events

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

On Feb 23 We went up Republic Creek to look at the stability of snow that has fallen over the last 2-3 weeks. We found a thin layer buried 2’ deep that showed potential to propagate and slide. We dug down 4 feet, just below the dirt layer that was deposited earlier this month. We got an ECTP30 that broke about 8" above that dirt layer. This was either on a thin layer of facets or preserved lower density dendrites. Photo: GNFAC

Cooke City, 2025-02-24