Boletín de aludes

Selkirk Mountains

Idaho Panhandle 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

The most problematic slopes are at mid and upper elevations where weak snow layers linger around a crust, and where you could trigger a larger avalanche. Light snow and southwest winds overnight likely formed thin drifted slabs on northerly and easterly-facing slopes helping stress weaker snow below. Back off steeper slopes if you encounter signs of instability and stick to wind-sheltered areas for safer riding options.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2

    Faceted grains lurk around an early-December rain crust. This weak interface ranges 18 to 24 inches deep across our forecast zones and the overlying slab continues to settle and stiffen faster than these weak grains are gaining strength. Most observed natural avalanches from our last storm cycle appear to have failed around this crust. Since signs of instability have wanned in recent days, you may get no warning signs before a slope avalanches.

    Avoid shallow areas near exposed rocks or below cliffs where it may be easier to impact weaker snow below a thinner slab. It may also take a larger trigger like a snowmobile or multiple riders descending the same slope to find the "not-so-sweet" spot and provoke one of these more dangerous slides. Persistent Slab avalanches can behave in surprising ways failing from adjacent to or below a slope. Give steeper, bigger terrain a wider berth and choose slopes with clean, open runouts without gullies or depressions below you.

Avalanche Discussion

Most mountain areas received 3 to 6 inches of new snow overnight Saturday. Moderate south-southwest winds likely deposited thin slabs on slopes that face northwest through north to southeast. The new drifted hazard today is expected to remain small and confined to areas below ridges and in cross-loaded gullies but expect these drifts to be reactive to ski pressure or side-hilling. While small surface hazards can often be managed with terrain-specific evaluations, these newly formed slabs overlap on the same slopes and elevations as our more concerning Persistent Slab avalanche hazard.

The stormy period on December 17 and 18 delivered around 8 inches of storm snow followed by moderate rain, then dense snow to cap things off. In the aftermath, the forecast staff observed natural avalanches that likely failed in weak faceted grains around the December 7 rain crust. These were not widespread throughout our forecast zones, but did provide a glimpse of our slab, weak layer behavior and potential avalanche size. Most slides failed on heavily drifted slopes around 6,000 feet or higher, broke wide across adjacent terrain features, and mostly pushed size 2.

Since the storm ended, we have not heard of any reports of rider-triggered slides, and the forecast staff has observed notable slab settling-stiffening from warmer temperatures. However, we continue to observe varying failure types in snowpack test in those same weak grains, and so we need to ask ourselves before committing to steeper slopes – why did this slope not avalanche? Uncertainty during a low frequency, high consequence regime warrants heightened snowpack evaluations, minimizing group exposure, and simply avoiding places where a shallow slide could provoke a deeper failure.

Be mindful of how close you get to steeper slopes above you as managing the uncertainty of persistent weak snow grains is the biggest challenge. Pay attention to how conditions change below your feet or machine as you move through the mountains and recognize potential avalanche size increases alongside increasing slab depth above. At the end of the day – when stability is the question, terrain is always the number one answer.

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