Bollettino valanghe

Banner Summit

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 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Dangerous avalanche conditions exist and human-triggered avalanches are likely. Fresh wind drifts are likely to be sensitive to your weight and are adding additional load to weak snow buried near the ground. Where this older snow exists, slides can be triggered remotely—from flatter 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
    Possible
    Dimensione
    2–3

    There is weak snow leftover from October storms buried in this zone. Snowfall over the past week has built a 3+' thick slab of snow on top of the old, weak snow underneath.  I went looking for this problem in this zone yesterday and I found it (watch the video at right). A series of unstable test results and an ugly weak layer were all I needed to see to convince myself that travel in avalanche terrain where old snow exists near the base of the snowpack was not in the cards.

    Buried weak layers like this can be very slow to heal. The snow that I saw yesterday certainly didn't appear to be in any hurry to do so. The additional snow that fell during the day yesterday is keeping this weak snow teetering on the edge of stability. Any avalanche that fails on this weak snow will be large and destructive. These types of slides are likely to behave in ways that surprise you. They may wrap around terrain features like ridges and may be triggered remotely—from flatter terrain below, above, and to the sides of steep slopes.

    While we've shaded the problem rose above to depict where you're most likely to trigger an avalanche, any slope harboring old snow (appearing as a mix of facets and/or crusts near the ground) is suspect. The difference between slopes that have old October snow and those that don't is fairly stark, but may be hard to identify without digging down, thanks to the thick slab of new snow. 

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Yesterday's storm brought 8-12" of snow to this zone. This snowfall was accompanied by steady moderate winds blowing out of the W/SW. This combination of new snow and wind is the recipe for building wind slabs. Slabs will continue to grow through the day today which will help to keep them sensitive to your weight.

    You are most likely to find these slabs in upper elevation terrain that is exposed to the wind. Look for drifts and dunes of new snow and for textures on the surface like ripples and waves to help you identify these slabs. If you are traveling along and you feel the snow stiffen under your skis or your machine you've almost certainly found a fresh slab. New slabs may be several feet thick and are likely to be reactive to your weight. These slabs are also adding weight to the weak snow underneath, exacerbating the persistent slab problem described above. Avalanches that initiate as wind slabs may step down to this weak snow, resulting in a much larger and more destructive avalanche.

Avalanche Discussion

PATTERNS ON PATTERNS For the past week, the picture in our area has been relatively simple, but not particularly pretty. Weak snow from October is buried on shaded middle elevation slopes and most upper elevation slopes. The best recipe for avoiding an avalanche problem was to avoid areas where this snow exists beneath the new snow that fell this week. Many folks have reported enjoying excellent skiing and riding conditions and good stability in areas free of the weak snow underneath. See, pretty simple. 

Yesterday's weather changed this picture, particularly in areas where more snow fell. A fresh round of wind slabs exist and will continue to grow throughout the day. These slabs are likely to be sensitive to your weight, particularly where they were deposited on subtle crusts and small facets that were generated during the cold, clear weather earlier this week. As the picture becomes more complicated, the amount of terrain that is available to us becomes more limited. In addition, our focus needs to be split in multiple directions: we are paying close attention to whether or not the slope we are on has old snow underneath and we are also thinking about the presence of wind slabs at the surface. When the backcountry world gets more complex taking a step back is generally a good idea. I'll be heading into the mountains today with this mindset, its a different world than it was yesterday.

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