Boletín de aludes

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Wed
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 3 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Triggering an avalanche large enough to bury you remains an uncomfortable possibility on slopes with old, weak snow at the base of the snowpack. Avalanches can be triggered after many tracks have already crossed a slope, and may break above you. Pockets of recently wind-drifted snow will be small but may be easy to trigger. 

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1.5–2.5

    Triggering large, destructive avalanches involving 1.5-2.5 foot thick slabs on weak, early-season facets near the base of the snowpack remains a possibility. The ingredients for this recipe live on all upper-elevation slopes and middle-elevation slopes on colder aspects of the compass (W-N-E). On colder slopes, an easily identifiable layer of weak, sugary facets sits underneath this slab. On more solar (SW-S-SE) aspects, the weak layer presents as a stack of facet + crust sandwiches and is more difficult to identify.

    Obvious signs of instability like recent avalanches, cracking, and collapsing have all been decreasing without additional snowfall — but not disappearing. Don't forget that the weak snowpack structure still lingers. Four out of the five people in your group could ride a slope and high-five at the bottom, while rider five triggers and is caught in a slide. Slides can break well above you on the slope.

    ADDITIONAL DISCUSSION:  Dense small wind slabs that are reactive to your weight remain a possibility near ridgelines today. In the Sawtooths, slabs also commonly form on the aprons below steep cliffs and couloirs. These will be small but can knock you off your feet in a consequential spot.  Small avalanches can be effective triggers for slabs failing on the weak snow near the ground. 

Avalanche Discussion

The Cambridge Dictionary defines persistent (adj) / per·​sis·​tent / pər-ˈsi-stənt as lasting for a long time or difficult to get rid of.  This, without a doubt, describes the weak facets we have in our snowpack that have lingered since late November and early December. These facets, or persistent grains, are what continue to keep our persistent slab problem alive and well. Most of you have gotten the picture by now that this problem is unfortunately not going anywhere, anytime soon. While it took a lot of force, I had a slab up to my chest fail in a snowpit and fall on top of me two days ago in the Sawtooths — I tried to bottle up and carry this experience with me while I continued on my tour. While hard to imagine, these slabs will be large, destructive, and potentially deadly if triggered. This is the time to ask the snowpack for permission, not beg for forgiveness. 

We are living in the doldrums of an avalanche problem that doesn't give us much reassurance it's there. Very few avalanches, and decreasing signs of instability like cracking and collapsing make it difficult for us to stay steadfast in our paths of making safe choices in the mountains. A secondary definition of being persistentis continuing to do something in a determined way even when facing difficulties or opposition. I implore you to be like the slab, and remain persistent in your thoughtful decision-making in the mountains. 

You'll head out into a cold wintry day with cloud cover, and some snowfall.  Pay attention to the minor instabilities involving our snowfall from the past week into today: small, dense, and sensitive wind slabs. These will be easy to identify and are unlikely to produce large avalanches on their own. But don't get distracted; remain persistent. The weak base of our snowpack must continue to be your primary concern. In this zone, a very dense, 1.5-2.5 foot thick slab is resting on top of these facets. This makes it more difficult to impact the weak snow underneath but also means that any triggered slides will be large and destructive. This weak snow will be more difficult to identify on solar slopes, where it exists as a mix of crusts and facets.  You're most likely to trigger these avalanches on steep, wind-affected slopes where the overlying slab has thin spots that make it easier to impact the weak layer. 

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