Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 3 years ago.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

Highlights

Triggering an avalanche big enough to bury you and your truck would take a bit of bad luck, but it is still possible. You probably will not see any warning signs before triggering a large avalanche. At upper elevations, the chance of triggering smaller, thinner avalanches will increase this afternoon. 

Heavy snowfall and wind will cause the danger to spike tonight and Thursday. If you're out after dark, expect dangerous avalanche conditions to develop. 

Avalanche problems

  • 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. Don't expect to see obvious signs of instability, like snowpack cracking or collapsing, before triggering a slide. 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 continues to be avoiding avalanche terrain, especially slopes with terrain traps or severe consequences in the event you get unlucky and trigger a big avalanche. 

    (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

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Periods of wind may have formed slabs in upper elevation terrain in recent days. This afternoon, increasing winds could begin forming the next generation of wind slabs. The fresh drifts will overlie weak snow (crust + facets, facets, surface hoar, or slick crusts) on many slopes, making the slabs especially easy to trigger in places. 

    Wind slabs and drifts could also produce thicker avalanches involving the February storm snow. While we have not observed many avalanches failing on this weak layer buried 1-2 feet deep, the resulting slide would be larger than you might expect. 

    Drifts, ripples, and dunes are clues the wind has been at work. If you see cracks shooting out in front of your skis or boards or feel the snow stiffen beneath you, the prudent move is to stick to gentler terrain. The wind slab avalanches could carry you where you don't want to go, and there's a chance they could trigger the Deep Persistent Slab avalanches described above. 

Avalanche Discussion

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. 

If this evening’s storm arrives earlier than forecast, expect to find thin, fresh wind slabs developing in exposed, upper elevation terrain this afternoon. The new wind slabs are burying extremely weak snow on many aspects and elevations. Small avalanches could be very easy to trigger and may release naturally.

Heavy snowfall and wind will cause the danger to spike tonight and Thursday. If you're out after dark, expect very dangerous avalanche conditions to develop.

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