Bollettino valanghe

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

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1 · Debole
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In sintesi

Triggering a large avalanche is unlikely.  Unstable slopes are becoming few and far between, but triggering a 1-3 foot thick avalanche may be possible on very steep, wind-affected slopes. You could trigger smaller avalanches where the wind has recently formed drifts. To reduce your risk, steer clear of obviously wind-loaded terrain where the snow surface is hard.

Problemi valanghivi

  • Persistent Slabs

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    Probabilità
    Possible
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    2

    Monday's strong NE wind event transported enough snow to maintain the threat of triggering a 1-3 foot thick persistent slab avalanche. In the Boulder Mtns (Galena Summit & Eastern Mountains zone), several 2-3 foot thick slides released naturally on W aspects with thin snowpacks. The slopes that failed are usually wind-scoured; you might find similar snowpack setups in isolated, exposed terrain in this zone. The weak layers we've struggled with all winter got a breather for much of the past couple weeks, but the recent wind-loading is stressing the thin, weak snowpack on some slopes.

    Are you likely to trigger a big slide on weak layers in the lower part of the snowpack? No.  But, if you were on a mission to hunt down one of these elusive persistent slabs, here's where I would look: exposed, wind-loaded terrain steeper than about 35 degrees, including cross-loaded gullies lower on slopes.

    If the snow surface is hard or you see cracks shooting out from your skis or sled, it's time to pay attention. Picture where an avalanche could carry you before committing to skiing or riding exposed avalanche terrain—the consequences of a triggering a powerful,1-3 foot thick, persistent slab should not be taken lightly.

    ADDITIONAL DISCUSSIONIn addition to the persistent slab problem above, there is a smaller—but more likely—problem you should also keep on your radar: fresh wind slabs. Monday's wind event formed hard drifts and slabs in some unusual places. Keep your eyes peeled for recent wind deposits near ridgelines, on the sides of gullies, and near large terrain features lower on slopes. 

     

     

Avalanche Discussion

Variety is the spice of life, right? You might have felt like our snowpack was already tricky to manage, but Monday's unusual NE wind event spiced things up a bit. We are dealing with two very different hazards right now:

  1. Despite the lack of fresh snow, strong winds blowing from an unusual direction (NE) were enough to put a large amount of snow “into play” yesterday. These winds quickly built thin, hard slabs where you don't usually see them. 
  2. The persistent weak layers (facets and depth hoar) buried in the lower half of the snowpack aren't ready to go quietly into this good night. Multiple natural avalanches in the Boulder Mountains and an avalanche failing on depth hoar near the ground in the White Clouds are clear indicators that large, destructive avalanches involving this weak snow remain possible.

Dealing with either of these problems individually is challenging in its own right, and the problems overlap on some slopes. The fresh, stiff wind slabs are adding additional weight, stressing the deeply buried weak layers. But that's not all; they are also adding stiffness at the snow surface, an important factor that allows the slab to “communicate” with the weak layers closer to the ground.  

I want to "paint the danger graphic green" and travel carefree in steep, consequential terrain as much as anyone. Unfortunately, we need to balance our thirst for those steep slopes with the lingering—but still real—threat of triggering large slides that could do more than just ruin a fun day. We're not out of the woods yet. 

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