Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Human-triggered avalanches are likely today, particularly on slopes where the wind has been drifting snow and adding weight to weak layers buried in the snowpack. Avalanches failing on weak snow buried near the ground will be very large and likely unsurvivable. Avalanches may be triggered remotely—from flatter terrain below, above, and to the sides of steep slopes. 

Read more about what CONSIDERABLE danger means in today's Forecast Discussion.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2.5–3.5

    Weak snow buried near the base of the snowpack poses a significant hazard here. This snow fell during the month of October and was preserved on many middle elevation slopes that face away from the sun (E-NE-N-NW), and on most slopes at upper elevations. The pattern of natural avalanche activity combined with our field observations indicate that this layer is at its weakest on the northern half of the compass. I made a video yesterday to try to help explain where you will find this snow and why that is important, you can watch it here. I think it is worth your time.

    In the Banner Summit area this layer is now buried 4-5+' below the snow surface underneath a very dense slab of snow. As this slab grows and stiffens it becomes harder and harder for us to impact the weak layer beneath. However, any avalanche that fails on this weak snow will be very large and destructive. Dropping the track of your sled into this weak layer is a "great" way to impact it. Large cornices collapsing and wind slabs failing in the upper snowpack can also be good triggers for deeper weak layers. Finding a place where the overlying slab is thinner, such as in steep, rocky alpine terrain will greatly increase your chances of triggering one of these monsters. Avalanches may be triggered remotely—from flatter terrain below, above, and to the sides of steep slopes. 

    (12/24/2021) Very large natural avalanche on "Marshall Slide" in the Sawtooths, on the shoulder of Williams Peak, above the Marshall drainage. This avalanche appears to have failed in the October facets deep in the snowpack. NE-aspect at 9,000'.

  • Wind Slabs

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

    This week's storm delivered snow totals measured in feet and a healthy dose of wind to go along with it. This combination built thick, stiff drifts on many upper elevation slopes as well as in exposed terrain at middle elevations. Be on the lookout for these slabs and know that you are likely to trigger them when you find them. A sudden increase in snow depth and snow density are great signs that you are traveling through a wind slab. Cracks shooting out in front of your sled, bike, skis, or board are clear indicators that you've found an unstable slab. Large dunes, ripples, and textures on the snow surface, and freshly formed cornices all indicate that the wind has been at work.

    Wind slabs will be 1-3+' thick, easily large enough to bury you should you trigger one. These slabs are hazardous in their own right and are also adding weight to the persistent slab problem described above. If you find yourself traveling in an area where both of these problems exist I would strongly recommend that you rethink your choice of terrain.

Avalanche Discussion

CONSIDERABLE AVALANCHE DANGER Today, the Avalanche Danger is rated CONSIDERABLEon slopes at middle and upper elevations. This marks the first day in almost a week that the danger has dropped below HIGH. Over the course of this week, intense storms have hammered the mountains with heavy snowfall and wind and countless natural avalanches have occurred. Yesterday, the storm exited our area and the snowpack was able to start adjusting to this new load.

If you carefully read what I have written above you will likely find yourself thinking, "Wow, that sounds scary"! You may also find yourself wondering, "Why the avalanche danger is decreasing if conditions are so hazardous"? If you find yourself in that boat, let me try to make it a bit more clear. When we talk about Avalanche Danger we are talking about the likelihood of an avalanche causing damage to something of value. For us as backcountry travelers, this object of value is you, your friends, family, and your riding and skiing partners. When storms are adding weight to the snowpack the likelihood of both natural and human-triggered avalanches are greatest. When loading stops the snowpack can begin to adjust to the added weight, but this is a process that takes time. The likelihood of natural and human-triggered avalanches is slightly lower than it was yesterday, but the outcome remains the same.

Today, you are likely to trigger large avalanches if you enter avalanche terrain. These avalanches are likely to be large and unsurvivable. Please give the snowpack the time it needs and the respect that it deserves. 

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