Lawinenlagebericht

Banner Summit

Sawtooth Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
Open full map
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Kernpunkte

Triggering a wide, 2-3 foot thick slab avalanche is possible in both sheltered and wind-loaded terrain. Ongoing wind and snowfall may build fresh, sensitive slabs in windy areas by nightfall. You can reduce your odds of triggering these thinner slides by avoiding slopes with stiff, wind-drifted snow at the surface.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    Several days of heavy, dense snowfall, rain, and warm temperatures formed thick, meaty slabs on most middle and upper elevation slopes. Multiple crusts are buried in the upper 3 feet of the snowpack, providing possible failure layers for the slabs above. 

    Assume the slab + weak layer setup exists on all slopes. You may or may not experience obvious signs of instability—like snowpack collapsing or cracks shooting out from your skis or sled—before triggering an avalanche. 

    As you change elevation and aspect, or travel through different drainages, you'll see significant variability in the buried crusts. This uncertainty makes it challenging to accurately predict which slopes are trouble and which are safe to ski or ride. You may be able to trigger avalanches remotely—from flat terrain below, above, and to the sides of steep slopes. 

    Additional Discussion: Weak, sugary, faceted snow in the bottom third of the snowpack is now buried 3-6 feet deep on W-NW-N-NE-E-SE facing slopes at middle and upper elevations. Triggering a huge slide on these layers is unlikely but would be unsurvivable. You're most likely to poke this beast in windy and/or rocky areas where the snowpack depth is variable.  

    (12/20/2025) Natural avalanche on an E aspect near 8900 ft in the Beaver Ck drainage in the western Smokys.

    Photo: Jeremy Lato

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–2

    You may find fresh wind drifts and slabs up to a foot thick in exposed upper elevation terrain. Watch for dunes or smooth pillows below ridgelines and cornices and on the sides of cross-loaded gullies. Cracks shooting out from your skis or sled are an obvious sign that you've found a wind slab. 

    Fortunately, the fresh wind slabs should be easy to spot and avoid. If you feel the surface snow getting stiffer, move to gentler terrain. Any wind slab you trigger has the potential to trigger the much larger Persistent Slabs as the wind slab avalanche moves downslope. 

    (12/18/2025) We found natural avalanches on the NE slope of the summit of Copper Mountain (8900 ft). These appeared to have released on Dec 17th and looked to be thin wind-slabs. Photo: Sawtooth Avalanche Center

Avalanche Discussion

Avalanche conditions are tricky. They vary from drainage to drainage and can change quickly as you round the compass or climb in elevation. Why? Over the past 10 days, we've added 6" of water to the snowpack, more than the previous 2 months combined! This heavy precipitation fell with punctuations of extreme wind and wild temperature fluctuations that sent rain lines above 9,000' on multiple occasions. These rain-on-snow events saturated the snowpack in some middle and low elevation areas, which will ultimately be a good thing for stability once it firms up again.

Climbing in elevation separates these rain layers with layers of snow, building a complex array of crusts or possibly crust + facet combinations as you climb in elevation. The variability here adds a healthy dose of uncertainty. Underneath it all lurks the most prominent weak layer of the winter, a stack of facets that should not be forgotten about in areas where the snowpack depth is around 3' deep, or in steep, rocky terrain where the snowpack depths are variable. 

We have many questions left to answer, but some may have to wait. Another 3-day storm arrives today. The Banner Summit zone will get the short end of the stick, but snow accumulations and wind will begin to freshen up the chance for wind slab avalanches in windy terrain. Enjoy the snow this holiday, but know that when conditions are complex, you can always choose simpler, lower-consequence terrain.

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