Boletín de aludes

Flathead Range & Glacier NP

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 7 months ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

A warming snowpack and buried weak layers will make it likely for you to trigger a large avalanche on steep slopes. Recent slides, shooting cracks, and fresh rollerballs are all signs of unstable snow. Enjoy the t-shirt weather by traveling on low-angle slopes, free from overhead hazards. 

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1.5–3

    Yesterday (Wednesday), riders in the Flathead Range intentionally triggered a large slab avalanche from the ridge above and noted a cycle of large natural avalanches. This continues a streak of instability (shooting cracks, collapses, avalanches) that started January 30th. The culprit is a weak layer of facets and/or surface hoar buried around a crust. Weak layers have been observed on all aspects, but the hotspot for recent activity has been on slopes facing north and east. 

    Steep slopes with 8+ inches of snow above the weak layer will present the greatest danger. On previously wind-affected slopes, the slab may be firm enough to support the weight of a rider.  Hard slabs deserve an extra level of caution. They may not give obvious signs of instability before failing and can break widely across the slope or well above you. Sustained warm temperatures can cause liquid water to move through the snowpack and further weaken these problematic layers. 

     Avalanches on this layer have been remotely-triggered from nearby low-angle slopes. In today’s heat, cornice falls or remote triggers could pull avalanches farther back onto ridges than you might expect. The prudent move is to stay off of and out from under steep slopes, and give ridgelines a wide margin.

     

    (2/4/2026)

    The crown of a human-triggered, slab avalanche in the Flathead Range. The rider triggered the slide from the ridge on a buried layer of surface hoar. It propagated widely (1000ft) and ran 700ft into the flats below. 

    Photo: Michael Reavis

  • Loose Wet

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

    Wednesday's wet loose activity was generally small in size. Clear skies overnight might have allowed surface snow to refreeze in some locations, especially at lower elevations. Refrozen surfaces will be slower to break down today; however, ultimately, I expect to find wet snow on all aspects and elevations.

    Move off of and out from under steep slopes if you (or your machine) start to sink into mushy surface snow.  Fresh rollerballs and pinwheels are also clues that wet surface snow is ready to avalanche.  Wet snow can fail as point releases or as slabs.  Even small amounts of moving snow have the ability to trigger a larger avalanche on buried weak layers (see Problem 1: Persistent Slab).

     

    (2/4/2026)

    Rollerballs, like these, are a sign that wet snow is ready to slide.  Move to lower-angle slopes anywhere you find mushy surface snow. 

    Photo: Flathead Avalanche Center

Avalanche Discussion

Keeping tabs on the number of thaws we’ve experienced this season has become a losing battle. The current thaw is notable though, as it's our first since burying a layer of faceted snow and surface hoar formed during the second half of January. This layer has been vocal from the onset, producing shooting cracks, whumpfs, and avalanches. Today’s warming might be its greatest stress yet. Furthermore, the potential for liquid water moving through the snowpack increases our uncertainty and is a good reason to widen your safety margins. Choose a zone that allows you an abundance of opportunities to skirt around steep slopes, obvious avalanche paths, and terrain traps.

Mike traveled in the Flathead Range Wednesday where he found many signs of instability, including recent large and destructive natural avalanches. Meanwhile, I toured in the northern Swan Range and found generally stable, albeit sloppy, riding. Both parties stuck to low-angle slopes to avoid triggering avalanches in wet snow or on buried weak layers. We enjoyed the sunshine and visibility, understanding that the riding conditions would not be the highlight of our day. 

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