Bollettino valanghe

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 7 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You’re most likely to encounter unstable snow on slopes with wind-drifted snow. This new snow is adding additional stress to the weak snow buried deeper in the snowpack. Even on slopes sheltered from the wind, these weak layers create conditions that make human-triggered avalanches a possibility today. Be aware of this possibility and plan accordingly as you travel in the mountains today.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    There are several layers of weak snow buried in our snowpack. Across the area, a layer of surface hoar can be found in the middle of the snowpack. This surface hoar has produced most of the human-triggered avalanches that have been reported to us this year. In addition, weak snow near the ground exists on many middle and upper elevation slopes. Triggering an avalanche on either of these layers would have harsh consequences.

    Persistent weak layers are difficult to deal with. They can produce avalanches many weeks after they are buried and they provide fewer and fewer obvious signs of instability as the days without a significant loading event pass. They can break wider than you might expect and may be triggered remotely, from gentle terrain adjacent to steeper slopes.

    Additional Discussion

    Winds have played a significant role in the slab formation portion of the avalanche equation in the past week. As time passes without significant amounts of new snow, these aging drifts are bonding to the surfaces that they were deposited on. However, the possibility of triggering one of the slabs remains, particularly in heavily loaded upper elevation terrain. These slabs are also adding stress to the weak snow described above.

Avalanche Discussion

This year, we’ve spent a lot of time talking about the surface hoar that was buried in early December. There is a good reason for that — this layer has produced dozens of human-triggered and natural avalanches. However, the complexity of the snowpack is increasing as the season progresses.

In addition to adding new snow, each storm buries a new interface to think about. Depending on the character of the older snow, the bond at this interface can vary significantly in strength. As the complexity of the snowpack increases, it becomes more and more difficult to confidently assess the stability of a given slope. 

Yesterday, in the southern portion of the Sawtooths, I found that a subtle crust accompanied by a thin layer of weak, sugary snow (facets) produced unstable snowpack test scores. This layer was buried by the storm that began on New Year’s Eve. Another week, another weak layer. 

You can try to limit some of the uncertainty present when dealing with complex avalanche problems by keeping track of these layers in the areas that you frequent. However, it's very important to recognize when you are dealing with a problem that is more complex than you can safely deal with. Unfortunately, this seems to be where we are headed this year. In this scenario, your best bet is to step back a bit and pad your uncertainty by building healthy margins for error into your travel practices.

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