Boletín de aludes

Swan Range

Flathead Avalanche Center
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Peligro de aludes

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

Lo esencial

Warm temperatures and direct sun will create dangerous avalanche conditions today. Rollerballs and snow falling out of trees are your clue that a wet loose avalanche cycle is starting. You can still trigger large avalanches on shaded slopes. Ridgelines and gentle terrain will provide the safest conditions and best opportunities for stunning views today.

Problemas de aludes

  • Loose Wet

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

    What skied well yesterday (Wednesday) will become a problem today. The 4-12 inches of dry snow that rests above a crust on W-S-SE aspects will become wet and slide as the sun warms the snow surface. Steep slopes that are directly exposed to the sun will be the first to manifest this problem. Rollerballs or snow falling out of the trees are your first clue that the surface snow is changing. Small point releases can entrain large amounts of snow and travel further than you expect, especially when sliding on one of several crusts in the snowpack. While slow-moving, an avalanche of this nature will be hard to escape and could easily push you over cliffs or into trees. Limit your risk by choosing slopes that are more shaded and/or less steep.

    Rollerballs such as these, will be the first clue that a larger wet loose cycle is starting.  Skitter your way to shaded and dryer slopes to manage for this problem.

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely
    Tamaño
    2–3

    NW-N-SE aspects above 6,000’ still harbor a weak layer of facets above a crust.  This combo is identifiable by digging down 2-4 feet until you find a thick and supportable crust. It is not always reactive in stability tests and can give the impression of being benign or stable.  It is, however, a low-frequency/high-consequence scenario. Natural and human-triggered avalanches have been reported on this layer within the last week. A common theme is that every time this weak layer is tested by a dramatic change to the snowpack (i.e. warming or loading), it has produced D2-D3 avalanches. Shallow, rocky, or convex parts of the slope are places to avoid.  Enjoy good snow on more gentle terrain or ribs between bigger slopes.

    Cornices have developed over the last several weeks. Any of these monsters that warm, sag and fall onto the slope below could be a likely trigger for a hard slab avalanche.  Move quickly out of paths that have large cornices looming above them.

    (3/9/2024)

    A crown of a hard slab avalanche on the north-northeast aspect of a prominent sub-peak directly southeast of Great Northern Mountain at 7400 feet. This may have failed in a layer of facets above the early February crust.

    Photo: Ernesta McIntosh

Avalanche Discussion

It’s all about trade-offs. Just when the forecast area seemed to be filled in and skiing/riding great, the clouds part and give way to warming temperatures and changing problems. 

The tricky part about the next few days is going to be managing wet snow and the lingering danger of persistent weak layers. As the snow on the sunny slopes transitions to wet, you will be forced onto more polar aspects. This shaded terrain still harbors several faceted crusts. Hard slabs failing on persistent weak layers have been well documented in the Whitefish Range and the Flathead Range over the last few weeks. We haven’t received any reports of natural or triggered avalanches in the Swan Range on these layers. Tuesday, an avalanche that failed on a buried weak layer, likely formed in early February, claimed the life of a backcountry skier near Lost Trail Pass south of Missoula.

With the sunset of the winter season just around the corner, we will have to hunt out the last powder stashes. As these get more affected by the warm weather, we’ll be driven to the precise slopes that harbor the recipe for large avalanches. Keep this in mind as FOMO begins to influence our decision-making.

As we transition into springtime travel, recall the cast of spring problems. Cornices that have grown over the last several weeks will begin to weaken due to sun and warm temperatures.  Limit your time underneath these hazards and stay well back from the edge while on ridgelines.

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