Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

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

Triggering a slab avalanche on weak layers 3-6 feet deep is unlikely. However, if you’re unlucky enough to find the wrong spot these slides will involve the majority of the winter’s snowpack. To reduce your risk, stick to lower angle terrain and avoid areas where the snow cover is thin.

Problemi valanghivi

  • Persistent Slabs

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

    Buried weak layers of facets and depth hoar sit near the base of the snowpack. These layers were responsible for the last slab avalanches reported in this zone (see photo) and remain our greatest concern. Triggering an avalanche on one of these layers is unlikely but the resulting slide will be massive. Unfortunately, knowing exactly when or where you’ll trigger one of these beasts is impossible to tell.

    Dealing with this problem is an odds game. Here are some considerations to help you reduce your risk: 

    1. Wind-loading: Slopes with stiffer snow near the surface–whether from wind-loading or "spin drifting" below large cliff faces–are more likely to produce big avalanches than areas where the surface is loose powder.
    2. Likely trigger points: You are most likely to impact the deeply buried weak layers on parts of a slope where the snow cover is thin, like near rocky outcrops. Heavily wind-affected areas where the wind created a complex pattern of scoured and loaded slopes are also more likely to be problematic.
    3. Slope angle: Avalanches are most likely in "prime time" avalanche terrain, slopes around 35-45 degrees in steepness. However, remember that persistent slab avalanches can be triggered remotely–from gentler terrain below or to the sides of steeper slopes.

    Additional Discussion:Yesterday, skiers in the Sawtooth Mountains found touchy wind slabs at upper elevation. Be alert to similar conditions today as W and NW wind forms drifts in exposed terrain. If the clouds hold off until later than forecast, loose snow avalanches are a possibility again this afternoon. These slides are most likely on sheltered SE-S-SW-W facing slopes while they directly face the sun.

Avalanche Discussion

Persistent slab avalanches remain our primary concern. Weak layers comprised of facets, crusts, and depth hoar exist across the whole of our forecast area. These layers are responsible for the vast majority of the avalanches we’ve seen this season. One primary factor that changes from range-to-range is snowpack depth. 

In our northern zones, these weak layers are buried 3-6’ deep. An overall deeper snowpack has fewer thin spots and thus provides less opportunity for a skier or rider to affect the weak layers near the ground. In our southern zones, the snowpack is shallower, providing more potential trigger points. 

So why is the danger the same across all zones? The avalanche danger is a balance of the likelihood of triggering a slide and the size of the resulting avalanche. So while you’re more likely to affect the weak layers near the ground in a shallower snowpack, the resulting slides will be smaller. I carefully chose the word “smaller” and not “small” because a 1-3’ thick persistent slab avalanche is plenty big to ruin your season–or worse.

Unless you buy a plane ticket to the Cascades, there's no way to completely avoid the widespread persistent weak layers near the ground. So what can you do? Over the last several days, we’ve been listing ways to reduce your risk. Write those key points down or screenshot the forecast and take it with you. Does the terrain you're considering share one or more of those characteristics?

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