Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The combination of snowfall, wind-loading, and buried weak layers make triggering avalanches possible today. You are most likely to trigger a slide in steep, upper elevation terrain where the wind has built slabs. You can dramatically reduce your risk of getting caught in an avalanche by sticking to wind-sheltered, mid-elevation terrain. 

Problemi valanghivi

  • Wind Slabs

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

    Steady snowfall and light to moderate winds have been the theme in this zone for most of the month of February (view storm totals here). This combination is a great way to form soft, but potentially reactive slabs. Wind slabs may be found near ridgelines or mid-slope in exposed terrain. Wind speeds are generally light in this zone and the evidence of wind loading may be subtle and may be masked by ongoing snowfall. It is safe to assume that most upper elevation slopes have experienced at least some amount of wind loading over the past week.

    ADDITIONAL DISCUSSION:A number of weak layers—both prominent and subtle—exist in the top 3' or so of the snowpack. The steady stream of light snowfall this month has gradually buried these layers, giving them little time to adjust to the loading. These layers have been responsible for a few human-triggered slides in the past week. On Tuesday, a snowmobile near Cape Horn Summit triggered two avalanches remotely (one is pictured at right/above). On Friday, a skier triggered a slab in very steep terrain. In addition to the weak layers in the upper portion of the snowpack, there is weak snow near the ground (depth hoar) in this zone. You'd have to be truly unlucky to trigger a slide this deep, but this layer has kept us out of the terrain where it is most likely to exist—namely very steep, rocky, and wind-affected upper elevation terrain.

    You can greatly reduce your chances of triggering an avalanche of any variety by avoiding "prime-time" slopes over about 35 degrees, especially in wind-exposed upper elevation terrain. Fortunately, that's also where you'll find the best skiing right now. 

    (2/16/2021) A snowmobiler triggered this avalanche from the bottom of the slope last Tuesday afternoon near Cape Horn Summit.

Avalanche Discussion

BIRTH OF A WEAK LAYER

If you've made it this far down the page you are well aware that we have layers of weak snow in our snowpack. In fact, we have several of them. You may find yourself wondering, where do weak layers come from? Well, they don't just spontaneously appear in the snowpack. Most often, they develop at the surface and are then buried by the next round of snowfall. 

When we are out in the mountains we are generally looking for the best surface conditions that we find. After all, skiing and riding powder is more fun than skiing and riding breakable crust. If you've been out in the past few days, looking for powder, you have probably noticed that there is a crust on top of the snow on slopes that face the sun. Depending on the conditions that they form in and how they are buried, crusts can make for long-lived weak layers. In fact, the combination of a sun crust with some small, weak facets on top was the weak layer responsible for the avalanche that resulted in the death of a rider in Smiley Creek on Friday. 

As we look forward to more snowfall overnight and another shot later in the week we can think about the surfaces that will be buried. If you want some homework, spend a bit of time mentally mapping where you are finding crusts today. If the crusts that we are burying this week end up being persistent weak layers you will have some sense where they are located and how to avoid them. Of course, weak layers can form without a crust too... It's never simple out there.

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