Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

Sun
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

You can trigger 2-3 foot thick slab avalanches that fail on widespread layers of weak snow. Avalanches can be triggered from long distances away from steeper slopes. Smaller avalanches involving only the new snow are possible on recently wind-loaded slopes. Smaller natural and triggered slides can step down to the weak layers below, creating much larger, more destructive avalanches. 

Problèmes avalancheux

  • Persistent Slabs

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

    Large, destructive avalanches failing on layers of weak snow buried 2-3 feet beneath the snow surface continue to be a very worrisome possibility here. Avalanches that failed on these layers in recent weeks have occurred across a range of aspects and elevations. Dig down and you'll find facets and/or surface hoar on shadier aspects and crust + facet combinations on sunnier slopes. These weak layers exist on most slopes.

    Slides that fail on these weak layers will break widely and can be triggered from long distances away from the slope that avalanches. You aren't likely to get obvious signs of instability involving this weak layer — the first indication of instability may be the large, destructive avalanche you trigger. Travel through the mountains knowing that triggering large, destructive slides is on the menu.

    (1/22/2024) The debris of this slide ran into a creek, a lower and mid-elevation terrain trap that is characteristic of the Banner Summit Zone. Terrain features like these multiply the consequences of these slides.

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    The recent storm brought 4-8 inches of snow to this zone, accompanied by generally light winds. An additional 3-6 inches is forecast to fall during the day today. Be on the lookout for minor issues involving this new snow. You may find relatively small wind slabs in exposed terrain and may be able to trigger dry loose sluffs on steeper slopes. New snow avalanches will be small but may run surprisingly quickly on the crusts and stiff surfaces underneath. Importantly, these smaller slides can trigger much larger, much more dangerous avalanches on the persistent weak layer described above.

Avalanche Discussion

We head into the weekend with a dangerous snowpack in our mountains. Here's a quick rundown: Uniqely widespread and fragile weak layers are resting under dense 2-3 foot thick slabs. Three hot, bright days started out the week, with temperatures rocketing into the mid 40s F in the mountains. A wet loose and wet slab avalanche cycle ensued. Thick crusts formed on solar aspects, with thinner, more fragile crusts on the solar margins (E/SE and W aspects). On shaded slopes you can find rain/rime/drizzle crusts that extend up to at least 10,000' underneath the new snow. Beginning Thursday, a warm, wet storm took aim at our area and delivered significant amounts of water to the mountains and valleys. The snowpack did not react kindly to this. Much less snow fell in this zone, and the likelihood of triggering large avalanches is lower than in our other zones, but the slides you can trigger are similarly large and destructive.

Yesterday, as I walked along a ridge above the East Fork of the Big Wood, I remotely triggered at least 4 large avalanches that failed on the prominent weak layer in the snowpack. One of these slides was triggered from over 1,000 feet away. All of these would have easily buried you, and some would have done much worse. These are exactly the types of slides that you can trigger today. Smaller slides involving the new snow will also be easy to trigger. Triggered slides can break down into he weak layer underneath, producing much larger, more dangerous avalanches. 

The pull of the fresh snow can be hard to ignore. I get it, I'm a hungry dog for powder just like you are. But you'll need to keep your focus on the hazards posed by the mountains in order to stay safe today. Avalanches can fail in places you've never seen them before, and can be triggered from the run-out zones beneath steeper slopes. Head into the mountains today with open eyes and a conservative travel plan, and work with your partners to stick to it. I'd love for everyone reading this to find a way to splash some powder across the smiles on your faces. But my biggest wish for you is to come home safe at the end of the day today, with good stories to tell, ready to go do it all again tomorrow. 

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