Boletín de aludes

West Slopes South

Northwest Avalanche Center
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Peligro de aludes

Mon
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

Human-triggered avalanches are likely on exposed slopes where the wind has drifted recent snow into dense slabs large enough to injure or kill backcountry travelers. Even in wind-sheltered areas, small avalanches could push you into cliffs, trees, or terrain traps. Avoid steep, wind-drifted slopes and assess sheltered terrain carefully before committing.

Problemas de aludes

  • Wind Slabs

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

    A powerful winter storm on Saturday brought strong to extreme winds and nearly a foot of snow to parts of the West South, creating widespread instability. Winds that strong form slabs in unexpected places, including far down the slope and in areas that are generally sheltered from the wind. These slabs can be many times deeper than the storm snow itself and often require a few days without further loading to stabilize.

    If you find yourself exiting a sheltered slope for something more exposed, take a pause and consider dialing back the objective. Better visibility may help spot chalky, pillow-like wind deposits, but the challenge lies in safely and accurately assessing their stability. Obvious red flags like shooting cracks and avalanches become less frequent as loading subsides. Use tools like hand shears, uptrack tests, and pole probes cautiously, keeping in mind they may not reflect conditions on the slope you're eyeing. 

    With continued cool temperatures, moderate snowfall, and ongoing winds, the safest move is to avoid any wind-loaded slope on Sunday. Stick to sheltered terrain, where not only is the avalanche danger lower, but the turns are likely more enjoyable.

    (12/14/2024)

    This skier-triggered wind slab avalanche on Saturday propagated widely across much of the slope. 

    Photo: Anonymous

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–1.5

    Reports across the zone point to somewhat upside-down storm slabs resting in sheltered areas outside of the wind zone. These instabilities are found either at the interface between the new and old snow or within the new snow layers. While we don't expect this problem to be particulary reactive on Sunday, triggering a slide remains possible in the right terrain, such as convex rollovers or unsupported slopes. Even though these storm slabs may not be large enough to cause significant issues on their own, the consequences could escalate quickly if triggered above trees, cliffs, or other terrain traps.

    Feel for hard-over-soft snow and use tools like hand shears, small and safe test slopes, and uptrack tests to help evaluate for storm slab reactivity.  

    (12/14/2024)

    Look just below the red line to see the crown of a storm slab avalanche on a rollover above a tree. Triggering even a small slide in this location can carry high consequences.

    Photo: Shane Robinson

Avalanche Discussion

It was a wild and windy day in the West South, especially near Crystal Mountain, where wind gusts exceeded 100 MPH! Crystal Pro Patrol triggered slab avalanches up to 2 feet deep during morning mitigation, and backcountry touring groups reported D1–1.5 storm and wind slab avalanches that were relatively easy to trigger.

The volcanoes also saw a significant shot of snow and wind, while White Pass received significantly less snowfall.

With tapering precipitation and decreasing winds, we expect avalanche danger to lower slightly and shift in character compared to Saturday. Natural avalanches are unlikely on Sunday, and the storm slab problem will become less widespread as the wind slab problem takes center stage. As a result of the strong winds, some of these slabs could be hard and break well above you on a slope.

A bit more snow is forecast overnight and if parts of the zone receive the upper end of the precipitation forecast, that could add to the hazard. Finally, the sun is likely to make a brief appearance on Sunday, and sunshine on fresh snow can increase the chances of snow shed and perhaps some increased slab reactivity on sunny aspects. 

If you get out, please share an observation with us!

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