Boletín de aludes

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Mon
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

Triggering a large avalanche is most likely on wind-exposed slopes at upper elevations. While less likely, there is a chance of triggering an avalanche in very steep, wind-sheltered terrain. Choosing gentler terrain protected from the wind is the safest option.

Problemas de aludes

  • Persistent Slabs

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

    Weak layers in the top few feet of the snowpack remain capable of producing avalanches. On Friday in the Baker Creek drainage, riders triggered three avalanches on upper elevation, wind-loaded slopes—one was remotely triggered from the ridgeline above (photo, photo). They broke 10-16" thick on a layer of well-developed facets that formed during the mid-winter drought. Another weak layer—a thin layer of facets atop a crust—was responsible for a small skier-triggered slide last Wednesday near the head of Smiley Creek. This layer has produced poor snowpack test scores in the northern Sawtooths (video above/right) as well as in the adjacent Banner Summit zone.

    Slopes having the right (or wrong) combination of weak layer and overlying slab are not widespread. In my mind, this is not a good thing! I would rather have unstable conditions nowhere, or everywhere. The spotty nature of the problem makes assessing each slope you want to ski or ride a gamble, and conditions are ripe for getting surprised. 

    You are more likely to trigger a persistent slab avalanche on wind-exposed, upper elevation slopes facing E-NE-N-NW. But it's also possible to trigger one on wind-sheltered slopes with "prime-time" slope angles steeper than about 35 degrees.  The best approach is to take a step back and choose more conservative terrain. The safest slopes are those protected from the wind and less than 35 degrees in steepness.

    ADDITIONAL DISCUSSION: NW winds today may blow last night's 1-2" of new snow into thin drifts. These are likely to be small, but worth looking for. Fresh wind loading is also adding more weight to the problem described above.

Avalanche Discussion

The distribution of an avalanche problem describes how common it is within a defined chunk of terrain. Avalanche professionals use a three-step scale to describe this distribution. If the problem is widespread, you'd expect to find it on most, if not all, slopes.  A problem with a specific distribution often exists in terrain with common characteristics—for example, wind-loaded slopes at upper elevations, or on slopes steeper than 40 degrees that face the sun. Last on the distribution scale are isolated problems—these are issues that are not common in the terrain, and there may not be a clear pattern that explains the presence or absence of the problem. Isolated problems often require knowing where to look—and what you're looking for—to find them.

Clearly, you could trigger avalanches in more places when the problem is widespread. So are widespread problems more dangerous? Most avalanche professionals would choose a widespread problem over one with an isolated distribution any day of the winter. Why is that? There is one thing we dislike just as much as mid-winter rain and 2-month dry spells—and that's uncertainty. When conditions are uncertain, most of us default to a state of unwarranted optimism—"oh, avalanches aren't that likely"—only to get unpleasantly surprised. The best way to manage this is by treating an UNCERTAIN snowpack the same as an UNSTABLE snowpack. In other words, take a more pessimistic approach. If we can't prove beyond a shadow of a doubt that the avalanche problem doesn't exist on a particular slope, then we consider it guilty.

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

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