Bulletin d’avalanche

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Mon
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

You could trigger a 1-2 foot thick avalanche in wind-drifted terrain and in the snowier, portions of this zone to the west of the Wood River Valley. Reduce your odds of triggering a slide by sticking to lower-angled terrain without steep slopes above you. Avalanches may be triggered remotely—from below, above, and to the sides of steep slopes.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2

    Our area continues to be plagued by a layer of faceted snow—in this zone, it's buried beneath a 1-2' thick slab. Since it was first buried in December, we've recorded nearly 400 avalanches—the vast majority broke on this persistent weak layer. Around 20 of these were human-caused. 

    Despite the lack of recent loading, we continue to see evidence that the snowpack remains dangerous in some areas. Observers in the neighboring Galena Summit & Eastern Mtns zone continue to report signs of instability—snowpack collapsing and cracking, as well as poor snowpack test scores. An unstable snowpack is less widespread in the Soldiers & Wood River Valley zone, but the snowpack in the Soldiers and the Smoky Mountain Crest near the head of Warm Springs is very similar to that of the Galena Summit area. Closer to the Wood River Valley, this slab is less common and instability is limited to areas with wind-drifted snow. 

    You can reduce the odds by avoiding slopes over about 35 degrees, especially those that have been affected by the wind. Pay attention to what's below you—look for trees, rocks, gullies, and other terrain traps. Given the possibility of remote-triggering slides, avoid terrain with steep slopes above you. 

Avalanche Discussion

FAQ's regarding the current snowpack, continued from yesterday...

Q: How do persistent weak layers like this one heal?A1: Through mechanical compaction or compression. When a very thick, dense slab overlies a weak layer, the sheer weight of the slab begins to "squash" the weak layer. Like a group of introverts stuck in a crowded room, at some point the faceted snow grains have no choice but to begin to connect. We're just starting to see this mechanism in action in the Banner Summit zone, where the weak layer is showing signs of relenting under the weight of the 3+' thick slab.

A2: Through rounding and bonding. When the snowpack is deep and air temperatures are warm, faceted snow grains will start to form bonds with one another through a process called rounding. At the same time, the sharp edges of the facets will soften and become rounder. In other words, the introverts slowly become extroverts.  Unfortunately, the snowpack in much of the forecast area doesn't qualify as deep (more than 3-4' deep), and the temperatures haven't been particularly warm. 

Q: Is there a way to tell when the snowpack has stabilized?A1: Unfortunately, there is no one piece of information that indicates a stable snowpack. Only through a cumulative lack of evidence pointing towards instability does a picture of improved stability emerge. So in other words, only once we stop hearing reports of avalanches (triggered or natural), collapsing/cracking of the snowpack, and poor snowpack test scores can we start to feel better about the snowpack. In much of the forecast area, folks are still reporting signs of instability. 

A2: Decreasing evidence of instability just tells us that the odds of triggering a slide are diminishing. As long as the slab over weak layer snowpack structure exists—and it will for some time, see above—the odds don't go to zero. There will always be "early adopters" who are willing to play the odds, and more conservative folks who like their chances of triggering an avalanche to be very, very low. Risk tolerance is a personal thing—I just encourage you to look at the "long game" and not just the odds of skiing or riding one steep slope.

Q: What happened this past week?A: Funny you should ask. Be sure to check out our latest Weekend Update where I attempt to answer just that.

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