Boletín de aludes

Flathead Range & Glacier NP

Flathead Avalanche Center
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Peligro de aludes

Mon
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 2 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

You're most likely to trigger a slab avalanche on slopes with wind-drifted snow. These may fail on buried weak layers, resulting in a larger slide. You could trigger smaller loose snow slides on steep slopes sheltered from the wind.  

Heavy snowfall and shifting winds will increase the danger overnight into Monday, especially in the favored Swan and Flathead Range.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely
    Tamaño
    1–2

    Triggering a large 1-2 foot thick avalanche on a buried weak layer is today's primary problem. This is more likely where the wind stiffened the surface snow into a cohesive slab. Suspect slopes include those with signs of wind effect, such as pillows, dunes, and etched surfaces. Buried weak layers (facets, faceted crusts, and surface hoar) are found on many slopes at all elevations and rest beneath February's snowfall. 

    Slopes that will be easier to trigger will be steep (35+ degrees) or associated with a convexity or rollover. Since the weak layers are not buried deeply, they should be sensitive to the weight of a rider in many locations. In deeper drifted areas, avalanches will be easier to trigger in thin spots at the edges or where rocks stick out of the snow.

    Observers in the southern Whitefish Range have noted signs of instability like collapsing (whumpfing), shooting cracks, and a triggered avalanche over the past few days. We suspect this could or is occurring in other zones as well. These signs are red flags directing you to lower-angle terrain free of overhead hazards. Thursday's avalanche (Attached image) confirms you can trigger avalanches remotely—from flat terrain below, above, and to the sides of steep slopes.  

    (2/15/2025)

    This image shows the skin track and approximate location where a remotely triggered hard slab avalanche occurred on 2/13/25. The slope angle varied between 30 degrees at the trigger point to 40 degrees at the crown. 

    Photo: Mark Dundas

Avalanche Discussion

Potentially heavy snowfall and increasing wind tonight into Monday will likely raise the avalanche danger, especially in the Swan and Flathead Range where the most snow is expected. We anticipate new snow problems, such as wind or storm slabs, to develop at the surface. Slides in the new snow will have the potential to step down to buried weak layers and trigger a much larger avalanche. The likelihood of a Persistent Slab avalanche failing may increase as the additional weight from snowfall and wind-blown snow will stress the weak layers formed during the January drought.

Saturday, observers in the southern Whitefish Range noted multiple signs of instability associated with January's buried weak layers. The FOFAC motorized Level 1 found buried surface hoar on north and south aspects with propagating results in their stability tests on southerlies, including an ECTP4 (Observation)! Another professional had two small collapses and one booming where two distinct stacked sun crusts and layers of buried facets existed on S-SW facing slopes (Observation). I visited the site of a remotely triggered avalanche and had propagating results with easy force at the east-facing crown. We also had a booming collapse with a spider web of shooting cracks (Observation).

Observed avalanche activity on the buried weak layers has been limited to intentionally triggered slides in the southern Whitefish Range on February 1 and a remotely triggered slide on February 13 (Observation). A natural cornice fall triggered a large avalanche, which stepped down to a buried weak layer in the Skyland area earlier in the week. We are unsure if a weak layer was the culprit in other recent slides.

The recent low-density snow and cold conditions have kept a cohesionless surface in many sheltered locations. On very steep slopes, riders could trigger loose snow sluffs. These can be problematic above cliff bands, in long-running gullies, or terrain traps where the snow piles up deep.

Upcoming Events: Check out our calendar and sign up now!

  • February 20-22nd: Avalanche Safety: Introduction to Avalanches Human Powered for Skiers and Snowboarders - register here
  • Feb 26th - Pint Night at Blackstar with donations going to Flathead Avalanche. State of our Snowpack presentation at 7 pm! 

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