Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

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

Human-triggered avalanches are likely today, particularly on slopes where the wind has been drifting snow. 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. 

Avalanche problems

  • Persistent Slabs

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

    Weak snow buried near the base of the snowpack continues to present 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 that we have observed over the past weeks, in conjunction with our field observations, indicate that this layer is at its weakest on the northern half of the compass.

    In the Banner Summit area this layer is now buried 4-5+' below the current snow surface underneath a very dense slab of snow. As this slab grows, it is making it harder and harder for us to impact the weak layer. 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, wind slabs failing in the upper snowpack, and finding a thinner spot in the snow cover are "good" ways to trigger these slides as well. 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. Moderate to strong winds blowing out of the S-SW yesterday and are in the process of shifting to blowing out of the W-NW today. As the wind shifts, freshly drifted snow will mask the presence of older, larger drifts underneath. Be on the lookout for these multiple generations of slabs and know that you will be likely to trigger one when you find it. A sudden increase in snow depth and snow density are great signs that you are traveling through a wind slab. Slabs will be 1-3' thick and easily large enough to bury you. 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.

    Even in places where the wind hasn't been blowing it is worth thinking about small avalanches related to the huge amounts of new snow. Steep road cuts and slopes above creek beds can present the sort of hazard that may seem benign at first glance, but even small slabs and loose snow slides on these features can quickly bury you. 

Avalanche Discussion

OLD SNOW AND WIND Your likelihood of being wrapped up on the wrong side of an avalanche today is highly dependant on two factors today: whether or not the slope you are on has old snow at the base and whether or not the wind has been at work. You can greatly reduce your risk by avoiding slopes that have either of these factors. Your highest risk is found where these factors overlap. Certainty when dealing with the snowpack is hard to come by, but I can tell you without a scrap of doubt in my mind: it will be a long, long time before you find me in terrain where these factors overlap. 

Pulling out of these very dangerous conditions that we find ourselves in is going to take time. It is possible, things can get better, but that day isn't today. And it won't be tomorrow either. Take a deep breath, slow down, and don't get lost in powder fever. This winter is young and we've already been fortunate enough to enjoy many days with deep, cold snow. Keep your safety margins wide today and enjoy the cold air and fresh snow.

Be sure to catch up on this week's conditions in our latest Weekend Update

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