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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In sintesi

Weak layers in the snowpack can produce large avalanches. You're most likely to trigger a slide in terrain that has been loaded by the wind, though slides are possible in steep, sheltered terrain as well. Thin, stiff wind drifts and slabs in wind-exposed terrain are likely to be small but may be easy to trigger. You can reduce your risk of triggering slides today by avoiding steep, rocky, wind-affected terrain.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    Several weak layers exist in the upper 1-3' of the snowpack here.  You are most likely to trigger slides on weak layers that are closer to the surface, like the surface hoar layer that has been responsible for a number of recent human-triggered avalanches (details here). However, slightly deeper weak layers also exist in this zone. It's a safe bet that most slopes harbor at least one of these layers of weak snow. You're more likely to trigger avalanches on slopes where the wind has built slabs and stiffened the snow surface (example), but slides are possible in sheltered terrain as well.

    Persistent slab avalanches behave in unpredictable ways, breaking wider than you might expect and high on the slope above you. Ski and sled tracks on slopes are not indicators of stability. In both of the last two reported human-triggered slides, multiple riders had been on the slope prior to the avalanche (take a close look at this photo). Don't expect to get direct feedback from the snowpack today—you are not likely to experience collapsing or cracking of the snowpack while traveling. The first obvious sign of instability may be the large avalanche you trigger. 

    Snowpack depths in this zone are highly variable, particularly in alpine terrain that is exposed to the wind. Triggering an avalanche on deeper layers can't be ruled out, particularly in steep, rocky, wind-affected terrain. 

    (1/15/2023) This avalanche was triggered by motorized users in Pole Creek, probably on January 14th. It likely failed on a persistent weak layer buried in the first week of January. 9200', N.

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Moderate winds have transported the few inches of recent snow into small wind slabs. You're most likely to find these near ridgelines and cross-loaded terrain features like gullies and ribs. These slabs are likely to be small, but may be able to knock you off your feet and send you downslope if they catch you unaware. Pay attention to the snow you are traveling through, if it is becoming denser or deeper you are probably moving through a wind slab. Cracks shooting out from your skis or machine are clear indicators you've found an unstable slab.

    If you are heading for steep, high-consequence terrain today, be thinking about these slabs. But be sure to recognize that the persistent weak layers described above exist in the same terrain. Triggered slabs can be effective triggers for deeper weak layers. 

    (1/22/2023) Wind transporting snow at sunset in the mountains above Smiley Creek.

Avalanche Discussion

We are seeing a significant distinction between the snowpacks in our region. Broadly speaking we can lump our snowpacks into two categories: deep and shallow. This Forecast Zone falls into the shallow category. Our deeper snowpacks are found in our northern and western mountains (Sawtooth and Western Smoky Mtns and Banner Summit Area Forecast Zones). There, our primary concern is the uppermost weak layer in the snowpack, a layer of buried surface hoar. The deeper weak layers in the snowpack are buried beneath very thick, dense slabs and impacting them with our weight has become unlikely (but not impossible). 

In this Zone, the picture is more complicated. Storms over the past month have dropped less snow here and the snowpack has remained thinner. Well-developed weak layers were buried in November, December and January (photo showing these layers). These layers are close enough to the surface that impacting them with our weight is easier. In addition, there is a lot of wind-swept alpine terrain in this Zone (picture the Boulders or the Pioneers) where snowpack depths vary significantly. This creates thinner portions of the snowpack where buried weak layers are closer to the surface and easier to impact with our weight. The thinner snowpacks also produce stronger gradients in the snowpack that make it harder for weak layers to heal quickly. This creates a state of weak layer purgatory, where the layers don't gain strength over time. 

Saturday, I went for a long tour near the boundary between the Galena Summit and Eastern Mtns and the Soldier and Wood River Valley Mtns Forecast Zones. My partner and I longingly looked at and then walked past many large avalanche paths that held thousands of feet of beautiful snow. The presence of the weak layers in the snowpack kept us from entering this terrain. Though triggering a slide wasn't likely, it was likely enough and the consequences were high enough that we didn't even discuss skiing this type of terrain.

I'll be completely honest, maintaining one's self-control when dealing with long-lived persistent slab problems is flat-out hard. I'm more than ready to be skiing big, open avalanche terrain, but the snowpack isn't quite ready for me. I'm not avoiding all avalanche terrain, but I'm definitely avoiding large, high-consequence terrain where triggering big, destructive slides is most likely: steep, wind-affected, alpine slopes with variable snow depths. 

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