Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

You can readily trigger large avalanches that fail in surprising ways on most steep slopes today, from valley bottoms to mountain tops. Avalanches will be larger and more destructive as you gain elevation and move into wind-affected terrain. Skiers and riders remotely triggered large to very large avalanches from hundreds to thousands of feet away on each of the past three days, and similar slides are likely again today. Our snowpack is complex and unstable — treat it with respect and build in wide safety margins.

Avalanche problems

  • Persistent Slabs

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

    Recent storms built a thick slab of snow on top of a widespread weak layer. Warm temperatures have allowed this slab to settle and consolidate. Skiers and riders remotely triggered large to very large avalanches involving this snow from hundreds to thousands of feet away on each of the past three days (photo at right/above). Large avalanches will be easy to trigger again today. Expect to be able to trigger them from a distance away and to see them break wide and fail in unusual locations.

    In sheltered terrain, expect to find slabs that are 1-2.5 feet thick. In terrain that has been affected by the wind, you'll find very dense, 2-5 foot thick slabs. Under these slabs, you'll find our primary weak layer of concern — surface hoar and/or facets on shaded slopes and a melt-freeze crust with facets on top on sunny slopes. Large natural and human-triggered avalanches failing on this weak snow have been observed on most aspects.

    Not enough weak snow for you? Further down in the snowpack, near the ground, another weak layer exists. Avalanches that step down to this layer of snow will send the entire season's snowpack rocketing downslope. This basal weak layer (located at the base of the snowpack) exists on upper elevation slopes and shaded middle elevation slopes. Avalanches that break down into this snow are likely to be unsurvivable. 

    This photo shows several large avalanches that were remotely-triggered by riders in the Beaver Creek drainage. The furthest away slide is over 800 feet wide, and failed a half mile from where the avalanches were triggered, out of sight on the right side of the photo.

  • Wind Slabs

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

    The persistent slab problem described above exists on nearly all slopes. If you do choose to tiptoe your way through all of the low and middle elevation terrain that is threatened by this problem, you may encounter some avalanche issues that involve only the most recent snow. In exposed terrain, expect to find some relatively small wind slabs that may be sensitive to your weight. Loose snow sluffs can be triggered in areas where the snow surface has remained dry. If you're finding warm, moist snow at the surface you may be able to push some sluffs that have a wet character. Any of these smaller slides can trigger much larger avalanches as they travel downslope. 

Avalanche Discussion

UNIQUELY DANGEROUS CONDITIONS

You will encounter a complex, recently loaded, unstable snowpack capable of producing very large and surprising avalanches in the mountains today. In the past 10 days, we've doubled our snowpack in many places, experienced a 36-hour long extreme wind event, watched temperatures flip between -40 F to 40 F, and weathered intense storms through 3 separate avalanche cycles. We have a uniquely bad weak layer in the middle of the snowpack that exists on nearly all slopes, and another widespread weak layer near the ground.  Riders and skiers have remotely triggered large to very large avalanches on each of the past three days. One of these slides was triggered from over a half mile away. Numerous avalanches have been observed at all elevations and all aspects, often occurring in places that don't frequently produce avalanches. 

Where are you going to get in trouble today? The Banner Summit Zone has a lot of smaller, less obvious avalanche terrain at lower and middle elevations. Here, you'll find many short avalanche paths that end in terrain traps. Imagine sharp road cuts, narrow gullies, and creek bottoms with steep slopes above them. While this terrain can be friendly when stability is good, it is deceptively hazardous on days like today. In recent days, we've seen many avalanches failing in this type of terrain, piling up debris deeply below. As you gain elevation you'll find increasingly thick slabs that have been stiffened by the wind. You can make very large avalanches here, the type that break hundreds to thousands of feet wide. Be suspicious of steep, snow-covered slopes at all elevations.

So how do we manage this problem? Travel through the mountains knowing that you can make large avalanches in many locations. And that the type and location of the slides you make may surprise you. You may find and trigger avalanches in places where you have never seen them before. Or you may see slides breaking much wider than you might expect. Head into the mountains expecting the unexpected today. Start with a conservative plan and stick with it. 

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