Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Anticipate loose snow avalanches in very steep, rocky terrain receiving direct sun. Triggering a large slab avalanche is most likely on steep slopes facing the northern two-thirds of the compass. 

Avalanche problems

  • Loose Wet

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

    This zone has recently received over a foot of snow, increasing the odds of loose snow avalanches on all aspects. The largest of these are most likely on very steep, rocky slopes receiving direct sun. These slides often initiate near the base of trees and rocks, gathering snow and growing in size as they move downhill. Rollerballs, or pinwheels, signify that the snow is heating up, and wet avalanches may soon follow. 

    While most will be small, they will be large enough to knock you off your feet and carry you into unwanted terrain. Even small slides can be consequential above terrain traps such as gullies, creeks, and thick timber. Plan your day to avoid lingering under steep, sunny slopes this afternoon.

    (2/18/2025) Sun-induced loose snow avalanches on Boulder Pk in the Boulder Mountains. Photo: Sawtooth Avalanche Center

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2–2.5

    Slabs that formed in early February rest above a variety of ugly, widespread, weak layers (facets, surface hoar, crusts, and combinations). Before triggering an avalanche, you're unlikely to experience obvious signs of instability like snowpack cracking and collapsing or whumpfing. Persistent Slabs can release in surprising ways and break much wider than expected. You are most likely to trigger a dense, 2-4 foot thick avalanche where:

    • The slab is less than about 2' thick—relatively shallower spots may exist where the wind frequently blows, and the slab is not uniformly thick.
    • Any part of the slope you are on or connected to is steeper than about 35 degrees
    • The slope faces the northern 2/3 of the compass
    • A smaller wind slab or loose snow avalanche overloads the buried weak layers (problem above)

    (2/17/2025) Avalanche on Sun Mountain in a thin snowpack near Ketchum.  Photo: Sawtooth Avalanche Center

Avalanche Discussion

We continue to receive reports of relatively stable conditions in the Banner Summit area, and triggering a large avalanche involving deeply buried weak layers is unlikely but not impossible. It will likely take a shadier, rocky, alpine cirque where the wind frequently blows, and the snowpack depth is variable.

Given the recent snowfall and a bit of wind, continue to look for and avoid steep slopes with obvious recent wind loading or signs of instability, like snowpack cracking or collapsing. Sluffing in very steep terrain is possible in dry snow on shaded slopes but is much more likely on any very steep slope soaking in the sun. Be aware of where even small avalanches may take you; terrain traps increase the consequence of being caught or buried.

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