Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
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Out of date — this forecast expired 6 years ago.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

Dangerous avalanche conditions exist. Triggering an avalanche is likely on steep slopes at upper elevations, particularly where the wind has helped to stiffen the snow. These slides will break 1.5-2.5 feet down from the surface on a thick layer of weak snow. Avalanches may be triggered from below, above, and to the sides of steep slopes. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Weak snow is buried 1.5-2.5 feet deep in this zone. This layer of sugary snow (facets) developed during the prolonged drought at the end of November and the beginning of December. A series of storms has gradually loaded this snow, creating numerous natural avalanches with each major loading event. Look at the photo to the right and the Media Gallery below for examples. 

    This layer of weak snow exists across our forecast areas. In the past two days, skiers have triggered 3 avalanches involving this snow in the Galena Summit area. In the Banner area, this layer is buried a bit deeper, which is a double-edged sword. While the likelihood of triggering it here may be slightly less, the consequences will be higher. In addition, you may receive fewer signs of obvious instability (like cracking and collapsing in the snowpack) as you travel through the mountains

    Your best bet for managing this problem is to avoid steep, upper elevation slopes, particularly those with recent and past wind loading. As a bonus for your caution, skiing and riding conditions are great in this low angle terrain right now, but don't forget about what is above you! Given the nature of our snowpack, remotely triggering an avalanche from below, above, and to the sides of steeper slopes is a possibility. Be aware of the terrain you are in and the terrain you are exposed to from above. 

    ADDITIONAL DISCUSSION - LOOSE SNOWSaturday's storm graced us with nearly a foot of low-density snow in this zone. Light winds since this storm have left this snow in place for the most part. With temperatures a few degrees warmer than yesterday we may see some small loose snow avalanches as the sun heats up slopes. In addition, if the wind picks up a bit (as forecast) we may see some small wind slabs forming near ridgetops. Though small in size, these may be touchy and will be adding stress to the weak snow described above.

    (12/23/2020) Large avalanche that released in the southern end of the Banner Summit zone. It broke hundreds of feet wide on weak facets buried in mid-December.

Avalanche Discussion

We are starting to see a fair bit of variability in the way our different forecast zones are behaving. However, there is an unfortunate constant across the region: a layer of very weak snow that developed during the November/December drought. The variation we are seeing between zones is driven by how deeply this snow is buried. In our northern zones (Sawtooth and Western Smoky Mtns and Banner Summit Area) this snow is buried by the 1.5-2.5 feet of snow that fell in the past two weeks. In our southern zones (Galena Summit and Eastern Mtns and Soldier and Wood River Valley Mtns) this snow is buried about half as deep. 

In addition to the depth of burial, the nature of the snow above these weak facets is important. In areas where the wind has helped to stiffen the overlying snow you are much more likely to experience cracking, collapsing, and to be able to trigger an avalanche. In areas where the snow above is soft and unaffected by the wind you are less likely to see these obvious signs of instability. Bear in mind that the new, low density snow may be masking signs of previous wind loading. If the character of the snow you are traveling through is changing from soft to firm the likelihood of triggering an avalanche is increasing. Unfortunately, even in areas that are completely sheltered from the wind, triggering an avalanche involving this weak snow is possible.

I suspect most of us are familiar with the expression "out of sight, out of mind".  With blue skies and blower snow, it can be easy to forget that we have built our snowpack on some of the weakest snow you can imagine.  Fortunately, you don't have to imagine it—put your shovel in the snow and you can find it! Encountering this snow in person is a great way to keep it at the front of your mind. You don't have to do snowpack tests, just get in there and interact with it with your hands. Every time I dig a snowpack I'm impressed by just how "ugly" this weak snow is. We are going to be dealing with this problem for a long time. I wish that weren't the case, but I don't have any control over the snow and neither do you. We only have control over ourselves. I will continue to advise you to exercise caution in your decision making in the mountains, not because I don't want you to have a good time, but because I want you to go home safely at the end of the day.

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