Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

The likelihood of triggering avalanches will increase throughout the day as the combination of 4-8" of new snow and wind builds reactive drifts and slabs in exposed terrain. These will grow in size and become easier to trigger as the storm progresses. Avalanches that break down into weak layers in the upper few feet of the snowpack are possible, resulting in larger, more destructive slides. You can reduce your risk today by steering clear of recently wind loaded slopes.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2

    Several weak layers exist in the upper few feet of the snowpack. A prominent layer of surface hoar buried 1.5-2 feet deep has been responsible for a handful of skier and rider-triggered avalanches in the past few weeks. This layer is at its worst on sheltered, shady (W-N-E) slopes. Above this, you'll find a few layers of crusts, facets, and/or surface hoar that were buried in the second half of January. Today's storm will be the first good test for some of these newer weak layers.

    Slides that fail on persistent weak layers are less predictable than simple wind slabs. They may break wider than you expect and may wrap around terrain features that confine wind slabs. Persistent slabs can break well above you on the slope you are skiing or riding on.  Triggered wind slabs can "step-down" to these deeper weak layers, resulting in larger, more destructive avalanches.

    (1/23/2023) Avalanche apparently triggered by a skier on Banner Summit. Slab depth and terrain characteristics are consistent with early January surface hoar layer. 7250', NNW. The date of this avalanche is uncertain, but likely occurred since Jan 18th. Photo taken Jan 23rd.

  • Wind Slabs

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

    Today's storm will bring 4-8" of snow to this zone. Moderate winds accompany this snowfall, blowing first out of the S-SE, then shifting to W-NW by mid-day.  Expect to see wind slabs building throughout the day, growing in size and sensitivity as they do. You're most likely to encounter a wind slab in exposed upper elevation terrain, near ridgelines and on the sides of terrain features like gullies and ribs. These features slow the wind down and force it to drop the snow it is carrying.

    As you travel through the mountains today, look for signs that the wind has been at work. Dunes, pillows, and ripples on the snow surface are all indicators that the wind has been transporting snow. If the snow you are moving through is becoming deeper and denser, you're likely moving through wind-deposited snow. Cracks shooting out from your skis or machine are a clear sign of an unstable slab. A variety of weak snow surfaces have developed in the time since our last snowfall, which may make today's slabs more reactive.

Avalanche Discussion

STEPPING BACK

Snowfall returns to our region today. In the past week, we've seen the likelihood of triggering avalanches gradually decrease. Today, we head in the opposite direction. While forecasted snow totals aren't in the same range as the monster storms early this winter, there will be plenty of new snow to change the picture out there. Your likelihood of triggering avalanches will increase throughout the day as the snow piles up. Today's snow is falling on a variety of snow surfaces, many of them weak. Surface hoar, facets, and crusts with facets on top have all been observed in the previous few days. This weak snow will make today's wind slabs more reactive than they would be otherwise. 

Moving our focus a bit deeper, we find several weak layers in the upper few feet of the snowpack. A few layers of surface hoar exist on sheltered, shady slopes, while crusts with and without facets on top can be found on slopes that face the sun. These weak layers will be stressed by today's storm, particularly in areas where the wind is building slabs. Wind slabs can step down to these weak layers, resulting in larger, more destructive avalanches. In this zone, the snowpack is generally strong and stable beneath these upper snowpack weak layers.

Today, it's a safe bet that conditions will become more dangerous as the storm progresses. Go into the mountains ready to take a step back from the type of terrain you played in yesterday. Choose your terrain with this in mind.

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