Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Isolated wind drifts may still be sensitive to triggering in upper elevation terrain. Look out for smooth, pillowed areas of snow close to ridgelines. If the sun comes out, there is potential for wet loose slides on steep slopes directly facing the sun.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1

    Some of the wind slabs formed by recent snowfall and wind are sitting atop weak layers that formed during our prolonged February dry spell. Slopes where you could trigger one of these wind slabs seem isolated, but do exist. Yesterday, a skier in the adjacent Galena Summit & Eastern Mtns zone intentionally triggered a small wind slab that was 18” thick. You’re more likely to find a wind slab sitting atop weak facets and/or crust sandwiches on upper elevation, NE-N-NW aspects.

    Look for evidence of wind drifting such as smooth pillows of snow, dune-like drifts, ripples on the snow surface, and fresh cornices along ridgelines. Cracks shooting out from your skis or board are a sure sign that you've found a sensitive wind drift. If the snow suddenly gets stiffer as you're moving on a steep slope, it's time to pay close attention and evaluate your terrain choices.

    ADDITIONAL DISCUSSIONIf the sun comes out, wet loose avalanches will be possible on steep, rocky terrain directly facing the sun. If the snow under your skis or sled is getting wet and mushy and you start seeing roller balls and pinwheels it is time to move on to cooler slopes. Wet loose avalanches have a tendency to fail naturally, so don’t linger under steep, rocky terrain that gets a lot of sun.

Avalanche Discussion

Looking back at these last couple of months, I probably don’t have to remind you that February and the first half of March were all about clear skies and sunshine. This dry spell created weak, faceted snow surfaces, especially where the wind or sun could not get to the snow. Nowhere was this dry spell stronger than in the Pioneers and the mountains around the Wood River Valley, and it got to the point where, in many areas, the snowpack was completely rotten and faceted top to bottom. 

When snow finally returned, it did so favoring precisely this southeastern part of the forecasting area. Adding the biggest load to the weakest snow resulted in some big avalanches (link to Bens North Fk picture) around the North Fork of the Bigwood River and in the Pioneers. 

Further north, in the mountains around Galena Summit, weak surfaces—while still common—were less widespread. This area also received less snow when the taps turned back on. As a consequence, avalanche activity has been more spotty, with smaller, shallower slides. 

This pattern continues as we move north of the pass and into the Sawtooths. A less severe drought, less precipitation in the latest storms and little to no slab avalanches. As you might guess by now, the Banner Summit Zone too follows this pattern, and wind slabs on weak crust-facet combination—while not possible to rule out completely—are few and far between.

So what does this mean moving forward? It looks like we might have more moisture on tap in the coming week, and if this turns out to be true, we will start seeing more buried weak surfaces becoming “active”. The further north we go, the more snow and wind will be required for this to happen, and the problem is unlikely to be widespread.

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