Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Dangerous avalanche conditions exist. Large human-triggered avalanches are likely in windy, alpine terrain. Expect loose snow avalanches to release on very steep slopes that directly face the sun. A much larger avalanche failing on weak layers deep in the snowpack could be triggered without warning. These massive slides will be large enough to snap trees. 

Avalanche problems

  • Wind Slabs

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

    This zone picked up 15-20" of snow since Wednesday evening, accompanied by moderate SW and W wind. Storm snow likely did not bond well where it landed on facets, crust + facets, slick crusts, and surface hoar. Expect to encounter a host of new snow problems. These range from sensitive wind slabs at upper elevations to potentially touchy slabs and loose snow sluffs that fail readily in steep, sheltered terrain. Look for obvious signs of instability, like small recent avalanches 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 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. ADDITIONAL DISCUSSION: This afternoon will be clear, sunny, and mostly calm. Expect naturally occurring loose snow avalanches on slopes that face the sun. These slides commonly initiate in rock bands on very steep slopes. These slides will run fast and far on slick crusts. Rollerballs or pinwheels are a clue that the snow surface is weakening, and loose avalanches may occur.

  • 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

The Banner Summit Zone has picked up steady snowfall since Wednesday afternoon. Bouts of moderate wind may have created some stiff drifts at upper elevations, but these may be hard to identify as they're masked by low-density snow.

We have limited information on how the weak snow surfaces under the storm snow are behaving, but reports before burial were less than glowing. There's enough new snow on these surfaces now that real avalanche problems may exist on slopes that are more sheltered from the wind. A long afternoon of sun will not only release natural loose snow avalanches but will rapidly consolidate the storm snow, quickly forming a denser slab on these weak layers that may be easy to trigger. Anticipate changing conditions today and think carefully about the consequences of being caught in an avalanche before committing to skiing or riding steep slopes.

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