Boletín de aludes

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Tue
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

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. 

Problemas de aludes

  • Wind Slabs

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

    Over the past 10 days, this zone has received a slow but steady trickle of snowfall accompanied by light to moderate winds. The low-density nature of the new snow has made it easily transported by even light breezes. Almost all open or sparsely treed, upper elevation slopes have experienced at least some amount of wind loading in recent days. Wind slabs may be found both near ridgelines and mid-slope in exposed terrain. The redistribution of snow by the wind continues to tickle the beasts buried in our snowpack, and you're more likely to trigger a persistent slab avalanche (Problem #1 above) on wind-affected slopes. 

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    There are two main persistent weak layers in our snowpack:

    1. Depth hoar exists near the ground on all aspects. This is the snow that we've been talking about all season long and seem to be destined to talk about for the remainder of the season.
    2. In the middle of the snowpack are several interfaces that have produced both avalanches and unstable test results in recent days. In this zone, these layers appear to be worst where they are accompanied by a crust.

    Observers traveling in this zone continue to report unstable snowpack test scores on the layers described above. I went looking for these problems just to the south of this zone yesterday and I found both of them. Near Dollarhide summit, I dug snowpits on shaded slopes and those that face the sun and got poor snowpack test results in both locations. You can read my observation here, and see a photo of those snowpits here. As I continued upwards, I found a large, natural avalanche that appeared to have failed on a crust before stepping down to weak snow near the ground within the last few days.

    You are more likely to trigger an avalanche on upper elevation, wind-affected slopes steeper than about 35 degrees. Triggering a wind slab (see Problem #2 below) could step down into these persistent weak layers, resulting in a much larger avalanche. Long story short, you can greatly reduce your risk of triggering a large persistent slab avalanche (or a wind slab avalanche for that matter) by sticking to wind-sheltered, mid-elevation slopes.

    (2/13/2021) This intentionally-triggered avalanche above Titus Lake initiated in a wind slab and then stepped down to the weak snow near the ground. While this event is a week out, similar avalanches remain possible.

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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