Bulletin d’avalanche

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Tue
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 7 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Continued snowfall and wind are keeping the avalanche danger elevated. You’re most likely to encounter unstable snow on upper elevation slopes with wind-drifted snow. This new snow is also adding additional stress on the weak snow buried deeper in the snowpack. Cautious route-finding and conservative decision-making are essential, particularly in upper elevation terrain.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    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.

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Continuing snowfall is providing ammunition for the wind. Although it has only been snowing a few inches each day, moderate winds are great at picking up this new snow and depositing it as slabs. Yesterday, as I traveled in the southern Sawtooths, I found fresh drifts up to 1 foot thick in upper elevation terrain. I avoided these slabs where I found them in terrain steep enough to produce an avalanche. 

    We picked up a few more inches of snow overnight and will see another few inches fall today. The wind will continue to build fresh slabs out of this snow and triggering one of these slabs is likely again today. These slabs pose a hazard in their own right, but are also adding stress to the weak snow buried deeper in our snowpack

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.

Régions couvertes