Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Sat
Alpine
4 · High
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 8 months ago. You’re viewing past conditions, not the current bulletin.

Highlights

A powerful storm is creating very dangerous avalanche conditions. Destructive natural and human-triggered avalanches are very likely. Stay off of and out from beneath slopes steeper than 30 degrees, and avoid traveling in the runout zones of avalanche paths. Slides may break wider, be triggered remotely and run faster + further than expected today.

Avalanche problems

  • Storm Slabs

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

    The intense loading of the past 24 hours and continuing throughout today has created dangerous avalanche conditions on most slopes, especially in wind-loaded terrain. You are very likely to trigger 1-3 foot thick slabs in both wind-loaded and sheltered terrain. Avalanches could release naturally, and cornices may fail, triggering slabs on the slopes below.  The size and reactivity of avalanches will increase as you climb into windier terrain at upper elevations.

    Look for wind slabs near or below ridgelines, along mid-slope ribs, and on aprons beneath chutes. Cracks shooting out in front of your sled or boards mean you've found a sensitive slab. You can manage your exposure to this problem by identifying and avoiding wind-loaded slopes, including the gentler terrain below large, upper elevation starting zones.

    In more protected terrain, look for shooting cracks and feel for "upside down snow" to identify and avoid triggering a storm slab. Where no slab exists, be weary of the amount of snow that seemingly small loose dry avalanches and "sluffs" may entrain and avoid terrain traps that amplify the consequences of even small avalanches.

    Avalanches could be wider than you expect, be very easy to trigger, and run faster + further where storm snow buried slick crusts, facets, crusts + facets, or surface hoar. Avalanches involving new storm snow will be dangerous on their own, but they also increase the chance of very large avalanches breaking on persistent weak layers buried deeper in the snowpack (Problem #2 below).

    (12/18/2025)

    We found natural avalanches on the NE slope of the summit of Copper Mountain (8900 ft). These appeared to have released yesterday and looked to be thin wind-slabs.

    Photo: Sawtooth Avalanche Center

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–3

    A couple of unstable weak layers exist below 2-3 ft (50-100cm) of snow. Intense loading (snow + wind) yesterday and throughout today is actively testing the limited strength of those buried layers. Avalanches involving these layers may be harder to trigger today, but will probably be very large and likely unsurvivable.

    We have continued to see cracking, collapsing, unstable test results, and natural avalanches related to the multiple crust/facet combos that are now tucked under a heap of new snow. The most suspect locations for these crust/facet combinations are W-NW-N-NE-E-SE facing slopes at middle and upper elevations (near and above ~8000' in this zone).

    Avoiding travelling on or below steep slopes where you suspect this weak layer to exist is your best bet to keep out of trouble today. The current snowpack is capable of producing very large, destructive avalanches. Some of these could run full-path to the valley floor.

Avalanche Discussion

We've been waiting for a storm to catch up from the slow start to winter... and this weather system is delivering BIG. Although we've all got powder fever right now, this is one storm that'll be best to wait for the dust to settle on. The widespread unstable persistent weak layers observed across all of our zones have yet to see this large of a load delivered over such a short period of time. Large avalanches are very likely, especially in the northern zones that receive the most snowfall. In areas where the late November/early December weak layers were previously buried by a couple feet of snow or where widespread stout rain crusts exist beneath the storm snow (specifically in the Banner Summit area), avalanches may not be as likely but will be much larger when they do fail.

Adding insult to injury, this multi-day storm event has delivered enough new snow and wind to create dangerous conditions even where an obvious weak layer is absent. These storm and wind slab avalanches may seem less "intimidating" than the persistent slab problem discussed above, but they could easily be large enough to bury you. If you've been sticking to sunny slopes that lack the early December weak layer, that risk management strategy will no longer be appropriate. 

What's the takeaway? Conditions are very dangerous, and the only reasonable approach is avalanche terrain avoidance. Stay off of and out from beneath slopes steeper than 30 degrees, and avoid traveling in the runout zones of avalanche paths.

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