Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

To reduce the chance of triggering large avalanches, avoid steep slopes where the wind has formed drifts or stiffened the snow surface. Wind features— and any avalanches you trigger— will become larger as you gain elevation. It would take some bad luck, but triggering much larger avalanches on deeply buried weak layers is not entirely out of the question. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    You could trigger wind slabs up to 3 feet thick in exposed terrain. Days of loading wind speeds formed slabs, drifts, and cornices near upper elevation ridgelines and in some middle elevation terrain, and today's winds may continue building slabs and wind features. In the craggy Sawtooth Mtns, watch for stiff pillows of snow at the bottom of large cliff faces, chutes, and couloirs.

    The fresh slabs rest above persistent weak layers (crusts, crusts + facets, facets, and possibly surface hoar) on many slopes. How could they behave?

    • Natural cornice fall could trigger wind slabs
    • You could trigger slabs remotely (from above, below, or to the side) - see photo
    • They could be very sensitive to your weight, even where the slabs are quite soft 
    • Avalanches may be wider than you expect

    Cornices, drifts, dunes, rippled snow surfaces, and chalky snow pillows are visible clues that the wind has been at work. Give large or overhanging cornices a wide berth. If you see cracks shooting out in front of your skis or boards, you've probably found a wind slab. If you feel the snow stiffen beneath your sled or skis, its time to steer clear of large or consequential avalanche paths. 

    (2/27/2024) This slab avalanche was triggered Tuesday from 50 ft away on a low-angle ridgeline. It broke widely in wind-drifted snow on a thin layer of facets above a crust. Cracks extended another 100' cross-slope beyond the crown. Smiley Ck, ENE @ 9,100'.

    Photo: Sawtooth Avalanche Center

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    It would take some bad luck, but triggering a large, destructive 3-5 foot thick avalanche isn't off the table yet. These slides would fail on persistent weak layers (crusts, crusts and facets, or facets) in the middle of the snowpack. You're most likely to trigger them on slopes facing W-NW-N-NE-E-SE in middle and upper elevation terrain, on slopes commonly exposed to the wind.  

    Persistent Slab avalanches can release in surprising ways. You can trigger them from flat or low-angle terrain long distances away from steep slopes, and they can break far above you. Before triggering an avalanche, you probably won't experience snowpack collapsing or other obvious signs of instability.

    ADDITIONAL DISCUSSION: While unlikely, we can't rule out the chance of triggering an unsurvivable avalanche involving faceted snow near the base of the snowpack. You're most likely to trigger one of these beasts in steep, rocky, wind-swept alpine terrain. Here, thin areas of the snowpack make it easier to trigger avalanches. Watch this video for more details. 

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