24-25
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 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
Images
Attached Videos
Snow Observation Source
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year
Snowmobile triggered avalanche likely on Saturday, Feb 22. It appeared that no one was caught or buried.
Avalanche Details: Persistent Slab Avalanches Tepee Basin
Southern Madison, 2025-02-23
Snowmobile triggered avalanche that resulted in a partial burial with no injuries on Friday, Feb 21.
Avalanche Details: Persistent Slab Avalanches Tepee Basin
Southern Madison, 2025-02-23
Snowmobile triggered avalanche that resulted in a partial burial with no injuries on Friday, Feb 21.
Avalanche Details: Persistent Slab Avalanches Tepee Basin
Southern Madison, 2025-02-23
Persistent Slab Avalanches Tepee Basin
Date
Activity
Snowmobiling
We got to ride into Tepee Basin with a pair of snowmobilers who were involved in an avalanche two days ago (2/23). The pair generously offered to join us and run us through the incident. It was an incredible opportunity to learn from each other. Read details about the slide.
The avalanche failed on the weak layer of facets that formed in late January. We also spotted another avalanche in similar, mid-elevation terrain likely triggered yesterday or earlier this morning. Both of these avalanches fit the pattern we've been seeing in Lionhead and the recent slide outside the forecast area in the Black Canyon area of Island Park. Other than the Black Canyon avalanche which is uncertain because we have not visited the site, the slides are taking place in mid-elevation terrain, smaller slopes with minimal wind-loading, and a thinner snowpack.
The snowpack in both the Tepee slides was thin relative to the average snowpack depth (129 cm).
Take Homes:
- You aren't good to go if you avoid the steep, upper-elevation, wind-loaded bowls. Steep slopes at mid-elevations harbor weak snow and have the potential for an avalanche.
- The persistent slab avalanche problem is alive and well. The epicenter of this problem is in the Lionhead area and the Southern Madison and Southern Gallatin Ranges.
- The issue with this avalanche problem is the distribution. It's nearly impossible to tell which slopes will slide and which ones won't. On many, the weak layer isn't so weak and the likelihood of triggering one is low. On other slopes, the weak layer is very weak and the likelihood of triggering one is up there.
Region
Southern Madison
Location (from list)
Tepee Basin
Observer Name
Zinn and Staples
Big Belts
Date
Activity
Skiing
Observation up in Big Belts North of Baldy, by the Hut meadow. 8600FT, 22 Deg Slope, NorthEast Slope. Open Meadow.
46.46385, -111.24431
Snow Depth, 225Cm+
Windy as hell. Thur - Sunday 40-70MPH above treeline from SW to W to South.
ECTN20 @195CM. Slabby Conditions from wind deposition but generally right side up snow.
Significant crowns in vicinity 2-6ft deep 200ft lengths in the steep E Facing bowls nearby.
Region
Out of Advisory Area
Observer Name
J Budreski
GNFAC Avalanche Forecast for Sun Feb 23, 2025
Snowpack and Avalanche Discussion
<p><span><span><span><span><span><span>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> can break hundreds of feet wide, and can be tricky as they might be triggered by the first person, or after multiple people have ridden a slope.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>On Friday in the southern Madison Range there were multiple rider triggered persistent slab avalanches, one of which partially buried a rider in Tepee Basin and was triggered after their group had put multiple tracks on the slope (</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>). Fortunately his arm and leg were visible and his partners got him out quickly and unharmed. Nearby, in the Taylor Fork, I triggered a “whumph” with a 100 ft long crack (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34298"><span><span><span><span><span><…;), and a group of riders triggered a few avalanches from flat terrain above a steep slope (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34327"><span><span><span><span><span><…;). </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Although the likelihood and danger has decreased, the potential large consequences of these avalanches remain unchanged. Be cautious of slopes steeper than 30 degrees, particularly at middle and lower elevations, as many of these slides are happening on mid elevation slopes with trees around (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=tAiSHSEDJhY&t=1s"><span><span><span… video</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34264"><span><span><span><span><span><… Canyon photos</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>). </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> are an additional concern. Although their potential size is relatively small, watch for fresh drifts that grow from today’s winds and old drifts that haven’t bonded yet.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Large, 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 the last couple days drifted snow into stiff slabs (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/wind-slab-hardscrabble"><span><sp…;). </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Near Cooke City and Island Park, today’s new snow and wind will create larger drifts that might be easy to trigger. Depending on how much snow falls during the day, by this afternoon </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> could become a problem on slopes where snow is not drifted. Warming temperatures might create density changes within the new snow that make avalanches easier to trigger. If there is more than 6” of new snow be cautious of all steep slopes, especially where even a small slide could push you into trees or over cliffs.</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 where above freezing temperatures melt the snow surface and make it sticky and wet. This is more likely near Bozeman and Big Sky where temperatures are warmer and there is a chance of light rain at lower elevations. Be careful of steep slopes with a wet snow surface.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Assess the snowpack for new and old drifts or a wet snow surface, and be extra cautious if there is heavy snowfall today. 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 first big warm-up with strong sunshine. 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