Lawinenlagebericht

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

Large human-triggered avalanches involving weak snow buried 1-2.5 feet down are likely. Smaller slabs of wind-drifted snow will be reactive and may step down to this layer, producing much larger avalanches. Pay attention to the terrain around you and above you—slides may be triggered from long distances away from steeper slopes.  Cracking and collapsing of the snowpack are clear indicators that the snowpack you are traveling in is unstable.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–2.5

    A layer of weak snow is buried beneath a 1-2.5' thick slab. This layer (crusts, facets, or a combination of the two) produced a widespread natural avalanche cycle last week, with slides observed on all aspects and at all elevations (incomplete list available here). Yesterday's new snow added weight and structure to the slab on top of this weak layer and observers reported experiencing widespread cracking and collapsing of the snowpack here. These are clear signs that this weak layer is struggling to support the overlying slab.

    Persistent weak layers are very tricky to deal with. And, as their name suggests, they tend to stick around for a while. Avalanches are possible in both sheltered and wind-affected terrain today, though you'll be more likely to encounter them where the wind has been building slabs. Remote triggering (explanatory video here) is also possible—a collapse on mellow terrain at the valley floor can travel long distances and release avalanches on steeper slopes above. Pay attention to the terrain you are in and to what is above you.

    Many lower and middle elevation slopes that face S-SW-W in this Zone were free of snow before last week's storm and this weak layer does not exist there. However, as you travel around the compass to colder aspects you will find this same weak snow.

    (12/2/2022) This avalanche failed on a N/NW-facing slope at 8,100' above the Lake Creek drainage near Ketchum. There were nearby ski tracks observed on the ridge and it may have been remotely triggered from above. It appears to have failed on the widespread layer of weak snow from the mid-November drought.

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    4-7" of snow fell here in the past 24 hours. Snowfall was initially accompanied by strong winds blowing out of the SE. Wind direction switched in the afternoon and moderate winds have been blowing out of the W since. These winds have built slabs in exposed middle and upper elevation terrain which may be sensitive to your weight today. Importantly, they are adding stress to the weak layers described in the persistent slab problem above. Triggered wind slabs and failing cornices can make for very effective triggers for deeper weak layers in the snowpack.

    (12/3/2022) The small wind slab was observed on December 3 onan E-facing slope at 9,300' in the Beaver Creek drainage. It likely failed thanks to an increase in wind speed reported by remote weather stations on 12/3. Older debris is also visible in this photo.

Avalanche Discussion

WALKING THE TIGHTROPE

The mid-November drought produced a widespread layer of weak snow across our Forecast area. An intense storm at the end of the month buried the weak snow and set off an impressive avalanche cycle. In the days since, every observation that we've received has reported cracking and collapsing in the snowpack. Yesterday's storm added 0.4-0.7" of SWE to the snowpack, helping the overlying slab grow and adding stress to the weak snow underneath. 

We are watching a balancing act take place in our snowpack. The slab builds and the weak layer tries to accommodate its weight. Natural avalanches fail in some places while other slopes teeter on the edge, just waiting for a trigger.  Our goal today is to steer clear of the slopes that are sitting at the breaking point so that we don't become that trigger. We are more likely to find slopes that are on that edge in places where the wind has been building thicker slabs. Paying close attention to the snowpack and terrain around us and the terrain that we are exposed to from above will help us to avoid being at the receiving end of one of these slabs. We are a long way from being out of the woods with this weak layer.

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