24-25

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

Wind slabs and thin buried weak layer

Date
Activity
Skiing

We went up Republic Creek to look at the stability of snow that has fallen over the last 2-3 weeks. Skies were overcast with light snow falling most of the day and winds were moderate with strong gusts.

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.

We heard of an avalanche that was triggered yesterday which broke 2’ deep and 250’ wide, possibly on this same layer, on an east facing slope by Mt. Abundance.

The wind was blowing new snow into fresh wind slabs. We were able to easily to trigger a couple wind slab avalanches on test slopes. More snow is expected tonight and tomorrow which will increase the likelihood and size of wind slab avalanches, and the added weight could cause a 2-3’ deep avalanche to break a couple hundred feet wide. Be cautious of steep slopes as new snow and wind build slabs over the next couple days.

Region
Cooke City
Location (from list)
Republic Creek
Observer Name
Alex Marienthal

Persistent Slab Avalanches Tepee Basin

Tepee Basin
Southern Madison
Code
SS-AMu-R3-D2-O
Elevation
9000
Aspect Range
E-NE
Latitude
44.90960
Longitude
-111.19400
Notes

Snowmobile triggered avalanches that resulted in a partial burial with no injuries on Friday, Feb 21 and a second slide on Saturday, Feb 22 with no one caught.

 

Number of slides
2
Number caught
1
Number buried
1
Avalanche Type
Soft slab avalanche
Trigger
Snowmobile
Trigger Modifier
u-An unintentional release
R size
3
D size
2
Bed Surface
O - Old snow
Problem Type
Persistent Slab
Slab Thickness
32.0 inches
Vertical Fall
250ft
Slab Width
100.00ft
Weak Layer Grain type
Faceted Crystals
Weak Layer grain size
1.50mm
Weak Layer Hardness
4F
Snow Observation Source
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year