Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The combination of snowfall, wind-loading, and buried weak layers make triggering avalanches possible today. You are most likely to trigger a slide in steep, upper elevation terrain where the wind has built slabs. You can dramatically reduce your risk of getting caught in an avalanche by sticking to wind-sheltered, mid-elevation terrain. 

Avalanche problems

  • Wind Slabs

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

    Overnight, 4-6" of fresh snow fell in this zone, accompanied by moderate winds. The mountains in this zone are lower in elevation than many of our other areas and the wind tends to be significantly lighter here. Regardless, the wind speed increase that was measured across the region likely occurred here as well. Wind slabs may be found near ridgelines or mid-slope in exposed terrain. It is safe to assume that most upper elevation slopes have experienced at least some amount of recent wind loading.

    ADDITIONAL DISCUSSION:A number of weak layers—both prominent and subtle—exist in the top 3' or so of the snowpack. The steady stream of light snowfall this month has gradually buried these layers, giving them little time to adjust to the loading. These layers have been responsible for a few human-triggered slides in the past week. On Tuesday, a snowmobile near Cape Horn Summit triggered two avalanches remotely (one is pictured at right/above). On Friday, a skier triggered a slab in very steep terrain. In addition to the weak layers in the upper portion of the snowpack, there is weak snow near the ground (depth hoar) in this zone. You'd have to be truly unlucky to trigger a slide this deep, but this layer has kept us out of the terrain where it is most likely to exist—namely very steep, rocky, and wind-affected upper elevation terrain.

    You can greatly reduce your chances of triggering an avalanche of any variety by avoiding "prime-time" slopes over about 35 degrees, especially in wind-exposed upper elevation terrain. Fortunately, that's also where you'll find the best skiing right now. 

    (2/16/2021) A snowmobiler triggered this avalanche from the bottom of the slope last Tuesday afternoon near Cape Horn Summit.

Avalanche Discussion

A DAY OF CHANGE

The past 24 hours were a transitional period for the snowpack. Over the previous 10 days, a steady trickle of snow gradually accumulated in much of our area. If you live in the Wood River Valley, this may be hard to believe, but I assure you it is true. Throughout this period, winds remained relatively light and temperatures were cool. That sounds like a perfect recipe for good skiing and riding conditions to me. Unfortunately, conditions changed significantly yesterday. Valley bottom temperatures climbed into the low 40s F and many ridgeline locations approached freezing (32F). In the afternoon, light rain was observed in several locations in the mountains north and west of Galea Summit. In addition, the wind speed increased dramatically overnight, with average speeds in the mid 20s and gusts above 50 MPH.

These three meteorologic events (warm temperatures, rain, and wind) mean that the snowpack you encounter today is different from what you might have found this weekend. Warm temperatures promote settling of the snowpack, which can add some heft to the slab of snow sitting on top of our buried weak layers. In addition, these warm temperatures combined with a dose of sun and some spits of rain introduced another crust to the snowpack in many areas. Crusts can form long-lasting weak layers in the snowpack if they are accompanied by facets (find a short video about this here). To top it all off, wind speeds increased significantly overnight. When strong winds blow they can work their way into areas that are generally sheltered, picking up the soft snow that has been hiding out there and building fresh slabs with it. As you head into the backcountry today, be alert to all of these changes within the snowpack. Its a new world every day out there. 

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