Bulletin d’avalanche

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Mon
Alpin
2 · Modéré
Limite forestière
1 · Faible
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

Unstable slopes are becoming few and far between, but triggering a 3-5 foot thick avalanche may be possible on very steep, wind-affected slopes at upper elevations. A smaller problem—but one that's more likely—is fresh wind drifting along high ridges and in alpine terrain.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1

    Westerly winds blew at moderate to strong speeds all day yesterday and continued through last night. While there is not a lot of loose snow available to be transported by these winds, snow professionals on Galena Summit yesterday found small but sensitive wind drifts (photo). Warm temperatures overnight may have helped these to stabilize. Long story short: I wouldn't expect wind slabs today to be particularly large or reactive to the weight of a skier or rider, but use caution on slopes that appear to be recently drifted. These wind slabs are likely to be stiff and may have the tell-tale surface texture that you can see in the photo. 

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–3

    Triggering a 3-5 foot thick persistent slab avalanche is unlikely. The weak layers we've struggled with all winter have not gone away, but the last part of January has given them the breather they've needed to become less reactive to the weight of a skier or rider. 

    Are there still slopes where it remains possible to trigger these layers? Probably, but it would likely take a dose of bad luck to find them. Ben was in the White Clouds yesterday where he witnessed some of this bad luck that fortunately turned to good luck. Riders in lower angled terrain collapsed the snowpack, causing a large alpine slope above them to crack, shift—and stop.  In his snowpit, he found especially weak early-season snow near the ground beneath a 4-foot thick slab of snow.

    This incident is a good reminder to keep these weak layers in mind and not completely write them off—especially given the consequences of triggering a persistent slab that's 3-5 feet thick. While the chances are small, there's a lingering possibility of triggering a large persistent slab avalanche—primarily on upper elevation and alpine, rocky, wind-affected terrain steeper than about 35 degrees.

Avalanche Discussion

With much of the forecast area trending towards Low avalanche danger, this is a nerve-wracking time to be an avalanche forecaster. This rings especially true with widespread persistent weak layers in the snowpack. Decreasing danger usually leads to more folks riding in steep terrain, which means more people testing your theory of the snowpack stability.

Our theory is that the persistent weak layers have had some time to adjust to the load from the first part of January. Especially in our northern and western mountains, they are buried deeply enough to be difficult to trigger. The weak layers aren't gone, they're just trending towards what we call dormancy and we probably haven't seen the last of them. The last slopes to stabilize in this scenario are usually the "baddest of the bad"—upper elevation/alpine, rocky, wind-loaded terrain steeper than 35 degrees. It would still take some bad luck to trigger an avalanche in these areas, but it's certainly not outside the realm of possibility. Ben's observation from yesterday—described in the persistent slab problem discussion above—provides a counterpoint to the otherwise improving picture of snowpack stability.

The danger scale is a very general description of the overall avalanche conditions. If you've read this far, you likely know that there are more subtleties and nuances to the avalanche danger than can be summed up by one word. As the avalanche danger continues to drop, we hope folks will keep in mind the weak layers under your boards or sled—even if they lie dormant for the moment. If forced to choose between Low danger with persistent weak layers, and Low danger without, I'd choose without each and every time.

Régions couvertes