Boletín de aludes

Banner Summit

Sawtooth Avalanche Center
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Peligro de aludes

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

Lo esencial

Conditions are dangerous. You could trigger large avalanches involving weak snow near the ground on many slopes. As you climb in elevation, both the size and chance of triggering avalanches increase. You could trigger slides from gentler terrain below, above, and to the sides of steep slopes. 

Problemas de aludes

  • Persistent Slabs

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

    Persistent Slab avalanches are tricky, and this problem can linger many days after it stops snowing. Some details:

    What and where is it? You could trigger 2-3 foot thick avalanches that fail on buried persistent weak layers—sugary facets or crust + facet combinations—near the bottom of the snowpack. Until proven otherwise, assume these old, weak layers of snow exist on all upper elevation slopes and on middle elevation slopes facing the northern half of the compass (W-NW-N-NE-E aspects).  Slopes where the wind formed drifts or stiffened the snow surface are most likely to slide.  

    How can you recognize it? The old crusts and sugary facets are easy to feel with your hands, ski pole, or snowmobile track (see photos and videos below). Recent avalanches, snowpack collapsing, and cracks shooting out in front of you are clear signs that conditions are dangerous.

    How can you manage it?  Sadly, the only surefire way to manage this problem is by avoiding avalanche terrain where the weak, older crusts or facets exist beneath the recent storm snow. Short of that, you can reduce your risk by avoiding large avalanche paths and those with ugly consequences if you are caught in a slide. Persistent Slab avalanches can break wider and higher on slopes (above you!) than you might expect. You could remotely trigger avalanches from gentler terrain below, above, or to the sides of steep slopes. 

    ADDITIONAL DISCUSSION: Today's unobstructed sunshine and light winds will increase the chances of sun-induced loose snow avalanches to release naturally, on their own. While these slides may not be big enough to bury people, natural or human-triggered slides could easily knock you over and carry you where you don't want to go. The small loose snow avalanches could also "step down" as they travel downhill, triggering a much larger Persistent Slab avalanche as described above. 

Avalanche Discussion

We've received plenty of observations in recent days (thanks!), and they share a couple of common themes: recent avalanches and snowpack collapsing. Nearly every observer—SAC forecasters, local professionals, and recreationists—reported fairly recent avalanche activity and/or snowpack collapses or whumpfs. Snowpack collapses occur on slopes where the snowpack is unstable but the slope is not steep enough to avalanche. 

The key to avoiding large avalanches today is pretty simple; don't travel on slopes where early season snowfall turned into crusts and old, faceted snow near the ground. These weak layers are responsible for nearly all of the recent avalanche activity and snowpack collapsing. The problem: we can't see the weak layers without digging or poking into the snowpack, and they don't exist on all slopes. To make matters worse, conditions, and snow stability, change dramatically over short distances as you climb uphill or move to shadier aspects.

The weak layer appears to be ugliest and most widespread in the elevation band that spans Middle Elevation and Upper Elevation terrain, from roughly 8000-10,000' in elevation. Below that elevation band, the early season snow melted off or is only a couple of inches thick and not as concerning. In the windy alpine environment above that elevation band, those weak layers appear to exist on fewer slopes. That is NOT a green light to shred the alpine; the weak snow near the ground exists, but it does not uninterruptedly blanket vast swaths of terrain as it does between 8000-10,000'.

While sunshine melted the early season snow on many SW-S-SE-facing slopes, it is easy to wrap around to a slightly shadier slope—with weak snow near the ground—without noticing. As you're moving to different aspects or gaining elevation, frequently check for the presence of crusts or sugary facets near the ground.

Regiones cubiertas