Boletín de aludes

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Tue
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

You are most likely to trigger an avalanche where the wind has stiffened the snow above weak layers in the upper snowpack. While less likely, there is a chance of triggering an avalanche in very steep, wind-sheltered terrain. You can significantly reduce your risk of encountering an avalanche by choosing gentler terrain that is sheltered from the wind. 

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    Multiple human-triggered avalanches have occurred in the past 5 days. All involved layers of weak snow in the upper snowpack. On Friday in the Baker Creek drainage, riders triggered three avalanches on wind-loaded slopes—one was remotely triggered from the ridgeline above (photo, photo). I looked at these slides on Saturday and found that they failed 10-16" down on a layer of well-developed facets that formed during the mid-winter drought. A different weak layer—facets on a crust—was responsible for a  skier-triggered slide on Wednesday near the head of Smiley Creek. These slides are clear indicators triggering an avalanche involving this weak snow is possible.

    Both of these weak layers (and others) exist in this zone. The combination of weak layer + slab is not widespread, but where it exists it is possible to trigger an avalanche large enough to bury you. You are most likely to trigger an avalanche that breaks on these persistent weak layers where the wind has built a stiffer, denser slab on top of them. Moderate to strong winds over the past weeks have affected the snow in both middle and upper elevation terrain. And while less likely, slabs failing in sheltered terrain can't be entirely ruled out. You can significantly reduce your risk of triggering a slide involving these layers on slopes that are less than 35 degrees that are sheltered from the effects of the wind.

    ADDITIONAL DISCUSSION: 1-2" of snow fell in this Zone on Saturday night. Winds blowing out of the NW transported this new snow into small, isolated drifts that may continue to be reactive to your weight today. While small, they may be large enough to knock you off your feet, which can have higher consequences in steep, rocky terrain. Importantly, these slabs are adding weight to the buried persistent weak layers described above.

Avalanche Discussion

We find ourselves in a tricky and fairly unusual situation this spring. Oftentimes, by this point in the season, we are dealing with a simple and predictable snowpack. Unfortunately, the prolonged drought during the months of January, February (and now March) left us with a smattering of weak layers in the upper snowpack. The presence and character of these layers varies from slope to slope and from Forecast Zone to Forecast Zone. What's more, instead of testing these weak layers with big storms we've been stuck with small storms that gradually build a slab of snow on top of these weak layers and provide us with little to no feedback about how these weak layers are reacting to the load along the way.

In the past week, we received some clear feedback that concern about these weak layers was well deserved: multiple human-triggered avalanches are clear indications that avalanches involving layers of weak snow in the upper snowpack are possible. The tricky part is that we need the find the right (wrong) combination of the slab and weak layer to make this happen. You can limit (but not completely eliminate) the slab portion of this equation by seeking out terrain that hasn't been affected by the wind. Remember that recent snow may be masking the effects of earlier wind loading. Seeking out slopes that are a bit gentler (less than about 35 degrees) can also help you reduce your risk. Don't forget that the danger is MODERATE for a reason today: human-triggered avalanches are possible. 

Catch up on what happened this past week in Scott's latest Weekend Update!

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