Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous avalanche conditions exist. Large human-triggered avalanches are likely in windy, alpine terrain. Smaller avalanches may also occur in terrain more sheltered from the wind. You probably won't see any warning signs before triggering a much larger avalanche failing on weak layers deep in the snowpack. These massive slides can be large enough to snap trees. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Last night's storm delivered 6-12" of low-density snow to this zone, accompanied by moderate SW and W wind. Storm snow will not bond well where it lands on facets, crust + facets, slick crusts and surface hoar. Due to these variable weak snow layers, expect to encounter a host of changing new snow problems. These will range from sensitive wind slabs at upper elevations to potentially touchy slabs and loose snow avalanches that fail readily in steep, sheltered terrain. 

    Look for obvious signs of instability, like small slides that released overnight or cracking and collapsing of the snowpack. Even smaller slides in sheltered terrain can have big consequences if they push you into one of the many terrain traps that lurk in this zone. Importantly, any smaller natural or triggered avalanche has the potential to step down to a deeper weak layer releasing one of the Deep Persistent Slab avalanches described below. 

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Triggering a wide, 2-4 foot thick avalanche large enough to bury people and possibly destroy a house remains possible, especially on the northern half of the compass (W-NW-N-NE-E aspects). Stout, buried crusts on sunnier aspects reduce the chances of triggering large avalanches on SW-S-SE aspects. 

    The odds you will trigger a Deep Persistent Slab are not high, but the consequences remain severe. Before triggering a slide, don't expect to see obvious signs of instability, like snowpack cracking or collapsing. You may be able to trigger avalanches from flat or low-angle terrain long distances away from steep slopes. Slopes with variable snowpack depths (windy areas, and craggy slopes with rocks or small trees poking out of the snow) are typical places to trigger Deep Persistent Slab avalanches. 

    Accurately evaluating whether a given slope is stable or unstable is challenging. Sadly, the only surefire way to manage this problem is to avoid avalanche terrain, especially slopes with terrain traps or severe consequences.

    (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.

Avalanche Discussion

Expect to find fresh wind slabs in areas exposed to the wind. The new wind slabs are burying extremely weak snow on many aspects and elevations. Smaller avalanches could be very easy to trigger and may release naturally, even on slopes more sheltered from the wind. 

The Deep Persistent Slab problem is a classic "low probability-high consequence" scenario. You're not likely to trigger these beasts, but you're playing a high-stakes game. Think carefully about the consequences of being caught in an avalanche before committing to skiing or riding steep slopes.

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