Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Tue
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
4 · Forte
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Very dangerous avalanche conditions exist. A very weak snowpack is being pushed past its breaking point. Large natural and human-triggered avalanches are likely on all slopes. Avalanches may be triggered from below and to the sides of steeper slopes.

The backcountry Avalanche Warning does not apply to the HWY 21 avalanche program.

Problemi valanghivi

  • Persistent Slabs

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

    A very weak snowpack developed across our area during the extended drought that came to a close last week. On Wednesday, just 4-8" of light snow was enough to create dangerous avalanche conditions in this zone. We observed both natural and human-triggered avalanches and recorded very unstable results in our stability tests. In the days since, the slab of snow has continued to gradually build with light snowfall each day. Yesterday and overnight, wet, heavy snow, low elevation rain, and warm temperatures helped this slab to rapidly consolidate. It is now 18-24" thick and large natural and human-triggered avalanches involving this slab are likely today.

    This type of avalanche problem is very difficult to manage. Avalanches may be triggered from long distances below and to the sides of avalanche starting zones. Small slopes and road cuts that generally pose little hazard will be easy to trigger today. Pay attention to the terrain that you are in as well as the terrain that you are connected to. Travel in avalanche terrain is not recommended.

    (12/18/2020) Avalanche in the Langer Creek area in the Banner Summit zone. It failed on very weak faceted snow that formed during the prolonged dry spell. 8000', NE

Avalanche Discussion

For weeks we have been talking about the incredibly weak snowpack that has developed in our region. We’ve explained that just because the snow is weak doesn’t necessarily mean it is unstable. A pile of sand doesn’t become unstable until we try to build our house on it. We started construction on the house last week and it is starting to get large, particularly in our northern areas.

The missing ingredient in the avalanche equation so far has been the slab. That changed this week. Much of our area has seen snowfall on each of the last six days. You can look at our Storm Table to get a sense how much your destination of choice has picked up. As the snow has fallen it has settled into a denser slab. It is bonding well to itself, but not to the weak snow underneath. Near freezing temperatures in the past 24 hours have helped accelerate this process, producing human-triggered avalanches even in the absence of significant new snow. 

The snowpack changes every day, but sometimes this change takes place much more rapidly than others. Times of rapid change are when it is easiest to get ourselves in trouble. Today is a good day to take a few steps back and think about the way you are traveling in the mountains. The hazards you are facing today are very different than they have been up to this point.

Regioni coperte