Boletín de aludes

Banner Summit

Sawtooth Avalanche Center
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Peligro de aludes

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

Lo esencial

You could trigger a 1-2 foot thick avalanche. Slopes with wind-drifted snow are the most dangerous. While unlikely, avalanches may also break on more deeply buried weak snow producing a very large and destructive slide. Avalanches can be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes. Wet snow avalanches are possible at low elevations this afternoon. Seek out dry snow and choose wind-sheltered, lower-angled terrain to reduce your risk.

Problemas de aludes

  • Persistent Slabs

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

    We have two potential persistent slab problems to consider:

    1. Growing Slabs Near the Surface: You could trigger a 1-2' thick slab avalanche on middle and upper elevation slopes. Snowfall over the past 10 days built a thin, soft slab atop weak layers of small facets or crust + facet combinations. Today's snowfall and wind will continue to grow the slab. The odds that you encounter an unstable slope increase substantially where this slab has been thickened and stiffened by the wind. Look for obvious signs of instability, like snowpack cracking or collapsing. These slides can be triggered from flat terrain—above, below, and to the sides of steep slopes. 
    2. Thicker, Older Slabs: While unlikely, the possibility of triggering a massive 2-5' thick avalanche remains on the table. These very dense slabs also rest on weak facets and crust + facet combinations. This weak layer has been "quiet," meaning we haven't seen any recent avalanche activity or associated obvious signs of instability, but the overall poor structure (slab over weak snow) is hard to ignore. Rapid loading during the next several days of heavy snowfall may be enough to bring this problem back to life. Smaller avalanches may generate enough force to step-down to this weak layer, producing an unsurvivable avalanche. 

    The combination of widespread weak snow, a rapidly developing persistent slab problem in the upper 2' of the snowpack, and the uncertainty associated with deeper weak layers should all combine to encourage conservative terrain selection. You can reduce your risk by avoiding slopes steeper than about 35 degrees—especially large avalanche paths and those with ugly consequences if caught in a slide.

    ADDITIONAL DISCUSSION: Today's storm will be less impactful near Banner Summit than in neighboring zones. Still, I'd expect to encounter thin, sensitive drifts in windier upper-elevation terrain. Look for them near ridgelines and on the sides of mid-slope terrain features like gullies and ribs. Surface textures like dunes, ripples, or pillows are clues that the wind has been at work. Cracks shooting out from your skis or machine are clear indicators that you've found an unstable slab.

Avalanche Discussion

The best way to reduce your risk is to avoid slopes where wind and new snow are forming sensitive drifts. I expect wind slabs to be a real problem at upper elevations. Some of these fresh slabs may release naturally, especially where they rest atop weak layers of snow in the upper 2' of the snowpack. Smaller natural or triggered avalanches may generate enough force to step down to more deeply buried weak layers. The resulting slide could be massive and unsurvivable. 

Adding to the day's uncertainty are the warm overnight temperatures and the threat of low elevation rain. The snowpack likely didn't freeze well in many areas last night, or may have only formed a thin crust with wet snow beneath. Today will be warmer than yesterday, and rain may fall up to 6,000'. The combination of these factors will push meltwater into the snowpack. When this happens, wet avalanches are possible, including wet slabs and wet loose avalanches that gouge near the ground. 

Today's avalanche conditions are much like the spring weather; dynamic and ever-changing. Expect to be surprised. Give yourself backup plans and safer exit routes expecting that avalanche conditions will worsen throughout the day. 

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