24-25 | Gallatin National Forest Avalanche Center

This snowpit on a SE aspect was made up of a dense slab of recent snow, sitting on top of many different layers of junky, faceted grains. Propagation was easy to find (ECTP 11, HS: 112). Photo: GNFAC

Avalanche Details: Whumpfs and Shooting Cracks in Sunlight Basin
Forecast link: GNFAC Avalanche Forecast for Sun Feb 23, 2025

Southern Madison, 2025-02-21

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Read more about Recent large avalanche Taylor Fork

We saw up to five recent avalanches from the last few days. 1-2 looked to have failed on PWLs, and the rest were wind slabs. Cornice collapses triggered at least two of these avalanches. Photo: GNFAC

Avalanche Details: PWL and Wind Slab Avalanches in the S Madisons
Forecast link: GNFAC Avalanche Forecast for Sat Feb 22, 2025

Southern Madison, 2025-02-21

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Unstable weak layers in the S Madisons

Date

Fri, 02/21/2025 - 14:00

Activity

Snowmobiling

Clear skies, sunshine and great visibility today allowed us to cover a lot of ground in the Southern Madisons. We traveled up the Taylor Fork to the weather station in Sunlight Basin, over to the head of Carrot Basin, through Sage Basin and up and over into Cub and Cabin Creeks.

Winds were light all day and only picked up later in the afternoon, gusting moderately from the south in the parking lot. Solar aspects moistened in the upper 1-2" of the snowpack, but we noted minimal signs of wet snow instability.

We came to the Taylor Fork searching for signs of instability from persistent weak layers and wind slabs, and we found both. We saw up to five recent avalanches from the last few days. 1-2 looked to have failed on PWLs, and the rest were wind slabs. Cornice collapses triggered at least two of these avalanches.

Outside of recent avalanches, a few other red flags jumped out at us. While traversing to our pit site in Sunlight Basin, we triggered a whumpfing collapse and a shooting crack up to 100' long across an adjacent slope. This snowpit on a SE aspect was made up of a dense slab of recent snow, sitting on top of many different layers of junky, faceted grains. Propagation was easy to find (ECTP 11, HS: 112). We also dug snowpits on N and SW facing slopes. While we found weak snow on these slopes, the N (ECTPX) and SW (ECTP25), the snowpack was deeper in both areas and the weak layers were less developed. When compared to what Alex and Mark found three weeks ago in this area, these instabilities are becoming less widespread and more stubborn to trigger, but an avalanche breaking on these weak layers is still possible.

Region

Southern Madison

Location (from list)

Taylor Fork

Observer Name

Haylee Darby

Still finding unstable weak layers in S. Madison - 2

Read more about Still finding unstable weak layers in S. Madison - 2

GNFAC Avalanche Forecast for Fri Feb 21, 2025

Snowpack and Avalanche Discussion

Persistent Slab avalanches are the primary concern. These slides will break 1-3 ft deep on weak layers that formed at the snow surface in late January. They can be triggered from a distance or the bottom of a slope, as demonstrated by slides triggered on Wednesday near Lionhead (<a href="https://www.mtavalanche.com/node/34264"><…;) and in the <a href="https://www.mtavalanche.com/node/34264"><… Canyon area</a> (east of Island Park, outside our advisory area). These weak layers don’t exist on all slopes, but they are widespread enough that all slopes should all be presumed guilty, until proven innocent (by digging multiple snowpits without finding the weak layer). Triggering large avalanches is LIKELY if you get on or near slopes steeper than 30 degrees.

Wind Slab avalanches are a more isolated concern, but there are probably still some places where drifts have formed and aren’t well bonded so you could trigger one. Temperatures won’t be too warm in these areas, so I don’t expect widespread wet loose activity, but it’s worth being on alert for if the sun pops out.

Conditions remain dangerous. The avalanche danger is CONSIDERABLE.

With winds picking up overnight, Wind Slab avalanches are the primary concern. There is lots of soft snow available for transport so expect deep drifts that will be easily triggered today. Keep watch for visual clues of drifted snow and steer clear of bulbous pillows that will generally have formed below ridgelines and cornices. Avoiding windloaded slopes will dramatically decrease your chance of triggering a large avalanche today.

Strong winds may limit melting at upper elevations, but on slopes that aren’t cooled by the winds, expect Loose wet avalanches as the day heats up and direct sunshine melts surface snow.

The avalanche danger is CONSIDERABLE on windloaded slopes and MODERATE on all other slopes.

The concerns in these areas are the same as in the Bridger Range, but winds are lighter this morning. This means that fresh wind slabs will be more isolated and Wind Slab avalanches not as easily triggered. Be on the lookout for those fresh wind slabs or older wind drifts that haven’t yet bonded to the snow beneath them.

Be on alert for Wet Loose avalanches as the day heats up. Cold powder from the last week will be seeing direct sunshine and warm temperatures for the first time today on many slopes. With lots of fresh snow, these slides may gain enough volume to really push you around or bury you in a gully.

The avalanche danger is MODERATE today.