Bulletin d’avalanche

Banner Summit

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 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Avoid steep slopes where you find evidence of windblown snow. Today's storm is creating fresh drifts that could be easily triggered—these will be most common at upper elevations. There is a chance that slides could break into buried weak layers, producing a more dangerous avalanche.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    New snow and wind are creating fresh wind drifts at upper elevations that you could easily trigger. In the past few days, there have been numerous reports of sensitive wind slabs—including one triggered on Friday by a heli-ski guide stomping cornices along a ridge in the Western Smokys (photo above/right). Today's new round of wind slabs could be more sensitive than the last batch—many will be forming on weak surfaces and slick crusts.

    Most wind drifts will be on the smaller side, enough to knock you off your feet or take you for a ride. However, wind slab avalanches could break down into buried weak layers within the top 1-2' of the snowpack—these are less likely but could be large enough to bury a person (example from a previous storm). 

    What should you do? Despite the same danger rating as yesterday, it'll be a good day to step back and choose more conservative terrain—especially at upper elevations. Be on the lookout for drifted or pillowed areas, and avoid steep slopes with evidence of recently loading.

    ADDITIONAL DISCUSSIONIf today's storm delivers the higher end of forecasted amounts (6" of new snow or more), there is the possibility of triggering small avalanches on steep, wind-sheltered slopes. The new snow may not stick well to weak, old snow surfaces and may slide as thin slabs or loose snow avalanches.

    (3/11/2022) A heli-ski guide triggered this small wind slab on Friday while stomping cornices along a ridge. It broke 12" thick and 100' wide, running on a slick crust. Western Smokys, 9000', E aspect. Photo: Sun Valley Heli Ski

Avalanche Discussion

Despite the same danger rating as yesterday, today will be more dangerous. Let's call yesterday a "soft" MODERATE, while today will be solid MODERATE. In zones that will get the most snowfall from today's storm—the Sawtooths & Western Smokys and Banner Summit—conditions could be on the upper end of the danger rating. 

If you've read this far, you know that the danger rating is only part of the avalanche equation. Normally 3-6" of new snow and wind would produce a fairly predictable wind slab problem. So what's different today? The 2 months of mid-winter dry weather, that's what. The drought produced a variety of weak layers that are unevenly distributed at both large and small scales. If you were to dig a snowpit on a perfectly wind-sheltered and shaded slope that was above the rain line during the late-Feb/early-March storm, you're likely to find a weak layer of sugary facets and maybe surface hoar down about 12-16". There are also newer weak layers closer to the surface. Unfortunately, once you move away from that "perfect" slope you're likely to find different snowpack layering. 

"Better the devil you know." It's an old saying that means something bad but known is better than something unknown. As we slowly add load to these weak layers—through wind loading today, and a forecasted wetter storm on Tuesday, there's uncertainty about how these layers will react. Avalanche forecasters don't like rolling the dice. Despite the MODERATE danger and relatively low likelihood of triggering a large avalanche, many avalanche professionals are becoming increasingly wary as we slowly add more load. Those of us at the avalanche center are tending to avoid steep slopes at upper elevations that are shaded (more likely to harbor weak layers) and wind loaded (adding more load to the weak layers).  

Catch up on what happened this past week in Ethan's latest Weekend Update.

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