Bollettino valanghe

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

You could trigger avalanches in areas with recently wind-drifted snow. These drifts are most widespread in alpine and upper elevation terrain. Some formed above slick surfaces, crusts, and weak snow so any avalanches you trigger could be wider and larger than expected. Small wet loose avalanches are possible on very steep, rocky slopes receiving direct sun. 

Problemi valanghivi

  • Wind Slabs

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

    Look for drifts of windblown snow near ridgelines and on the sides of cross-loaded gullies and chutes. These will be most common at upper elevations but you may find some slabs at middle elevations as well.

    These slabs are likely to be less than a foot thick. Some of them formed on slick, icy crusts and small facets. This means they may be easy to trigger, break wider than expected, and could pick up speed quickly as they travel downslope. This slab avalanche (observation) was triggered by a skier yesterday in the W. Smokys. It's a good reminder that even small slides can be consequential if they drag you through trees or push you into a creek bottom.

    If you find the snow depth is quickly increasing or the surface is becoming stiffer, you've found a wind slab. Cracks shooting out in front of you are an obvious sign of instability. Some of the new slabs will be on the smaller side, but some are large enough to bury people. Think about where even a small avalanche would carry you before committing to riding or skiing any recently wind-loaded slopes. 

    ADDITIONAL DISCUSSION:Wet loose avalanches are possible today. Theyare most likely on very steep slopes that face the sun, especially where the snowpack is less than about 2' thick. Even small wet avalanches are much more powerful than you'd expect (see videos here and here). Pay attention to the terrain above you. Large slopes can produce slides big enough to knock you off your feet and carry you places you don't want to go. 

    (3/11/2022) A heli-ski guide triggered this small wind slab on Friday while stomping cornices along a ridge. It broke 12" thick and 100' wide, running on a slick crust. Western Smokys, 9000', E aspect. Photo: Sun Valley Heli Ski

Avalanche Discussion

UNCERTAINTY 

Yesterday, a skier triggered a small slab avalanche near the head of Smiley Ck in the W. Smoky Mountains. The slide failed on a thin layer of facets that formed above a stout rain crust (see pit photo here). The avalanche broke 150' wide and 6-10" deep, piling debris against a line of trees near a creek bottom (see observation and photo here). 

Multiple layers of facets exist in the upper 1-3' of the snowpack. You may find facets (shady aspects), crusts (sunny aspects and some rain crusts on all aspects), crusts + facets (mixed sunny/shady aspects), and possibly surface hoar. The complex nature of where these layers exist (or don't) makes it hard to pin down a large-scale pattern on which slopes or layers are most worrisome. 

It's unclear if yesterday's avalanche was an indication of a larger pattern, or simply an example of a "sweet spot" where a particularly touchy weak layer and subtly wind-affected slab overlapped. With better visibility this morning, we hope to get some answers to this question. Regardless, it's a perfect example of the type of complexity we're dealing with out there. 

While somewhat unsatisfying, the best way to face uncertainty is to scale back our terrain choices. Slides involving these layers are most likely on recently wind-loaded slopes that are over about 35 degrees. Remember that even light wind can be enough to tie together a slab. Cornices and stiff drifts are great indicators, but clues can be more subtle too. Look for shallow "dunes" and ripples in the snow surface or dig a quick hole with your hand to see if the slab stiffens quickly under the new-fallen snow.  

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