Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Dangerous avalanche conditions exist and human-triggered avalanches are likely. Avalanches are most likely in areas where the wind helped to build thicker drifts, but slopes sheltered from the wind are hazardous as well. Avalanches may be triggered from below and to the sides of avalanche starting zones. Thin wind slabs forming today will be reactive and may be able to trigger avalanches on deeper weak layers in the snowpack as they travel downslope. 

Problemi valanghivi

  • Persistent Slabs

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

    In the past 36 hours, the widespread layer of very weak snow that exists in our area was pushed past its breaking point. I was out in this zone yesterday and after the rain stopped falling I saw evidence of a widespread natural avalanche cycle. Nearly every steep slope I could see had avalanched. Overnight, skies cleared and temperatures cooled a bit, allowing the snowpack to start to refreeze after yesterday's record high temperatures and rain. This process is helping the snowpack to stabilize, but this is happening very slowly. Today, avalanches on this weak snow will continue to be easy to trigger, particularly in areas where the wind built thicker drifts. 

    Wet snowpacks behave unpredictably. Very weak snowpacks also behave unpredictably. The snowpack in this area is both of those things. Expect the unexpected and continue to build wide safety margins into your backcountry travel. Avalanches may be triggered from long distances below and to the sides of avalanche starting zones. Pay attention to the terrain that you are in as well as the terrain that you are connected to. The avalanche warning has expired but today is not the day to let your guard down.

    (12/21/2020) Persistent slab avalanche that failed on the weak, faceted snow that developed during the extended drought. This slide failed on a N-facing slope at 8,000' in the Banner Summit Zone.

  • Wind Slabs

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

    A few inches of new snow combined with moderate to strong wind will build a fresh batch of wind slabs this morning. These slabs are likely to be small and isolated, but may be sensitive to your weight and large enough to knock you off your feet or sled. Be on the lookout for these slabs in upper elevation terrain that is exposed to the wind. An avalanche that starts as a small wind slab has the potential to step down to deeper weak layers buried in the snowpack, resulting in a large and dangerous avalanche.

Avalanche Discussion

As avalanche forecasters we spend a lot of time thinking about uncertainty and confidence. Thinking about these things helps us to produce forecasts that are both accurate and useful for you as a reader (at least, that's the idea). On days when we have a lot of information about the snowpack and the weather is simple, we can have high confidence in how the snow will behave. When the weather is changing rapidly and we find ourselves dealing with snowpacks that are unusual, our uncertainty can be high. Today is the later. 

There is no reason to hide the fact that we have a lot of unknowns and a lot of unknowables in today's snowpack. The widespread layer of weak snow buried in our snowpack is quite unusual, a once in a decade or two sort of thing. The warm, wet weather that we just experienced is also quite unusual for this time of year; Stanley set the record for highest temperature seen on the solstice, breaking a record that was set over 50 years ago. Because of the combination of these things I have a lot of uncertainty about how our snowpacks will behave. The first step in dealing with uncertainty is to acknowledge its existence.

After I issue my forecast this morning I will take off my forecaster's hat and put on my backcountry traveler's hat. When I walk out the front door I will expect to see things that will surprise me. We only see what we are looking for, so I'd advise you to have your eyes open to everything. You can manage the uncertainty by increasing your safety margins today. 

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