Bollettino valanghe

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Sawtooth Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Conditions are dangerous. You could trigger large avalanches on many slopes that have enough snow to keep your skis or sled from hitting the ground. As you climb in elevation, both the size and chance of triggering avalanches increase. Avalanches may break wider than you expect. You could trigger slides from gentler terrain below, above, and to the sides of steep slopes.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    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—on slopes where more than a few inches of old snow existed before the December storms. Until proven otherwise, assume these old, weak layers of snow exist near the bottom of the snowpack 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: Fresh wind slabs formed in exposed upper elevation terrain over the weekend. While they will not be as touchy (easy to trigger) as when they initially formed, we can't ignore them. Look for these slabs near ridgelines and on the sides of mid-slope features like ribs and gullies. Textures like dunes, ripples, and pillows indicate the wind has been at work. Cracks shooting out in front of you are a clear indicator of instability.

    Any small wind slab avalanches you trigger could "step down", creating a much larger Persistent Slab avalanche as described above. 

Avalanche Discussion

Ben spotted a fresh avalanche yesterday on a northerly aspect near Titus Ridge (Timber Bowl, photo). This slide was about 500' wide and likely failed on the weak facets near the ground. Also, observers continue to report frequent snowpack collapses or whumpfs (View Observations) in the three northern forecast zones. 

The key to steering clear of large avalanches seems pretty simple; don't travel on slopes where early season snowfall turned into crusts and old, faceted snow near the ground. The crux: you 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.

Regioni coperte