Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

To reduce the chance of triggering avalanches, avoid slopes where the wind recently formed drifts or slabs. In areas more protected from the wind, triggering a 1-2 foot thick avalanche is less likely but not out of the question. Pay attention to the consequences of being caught in even small slides in terrain with rocks, cliffs, trees, and terrain traps.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2

    What is it? Recent storms have favored this zone and buried newer weak layers consisting of facets or crust+facet combinations in the upper snowpack. These layers are more dangerous where recent winds have added weight to the slab. It's been almost three weeks since the last reported avalanche in this zone that involved buried surface hoar down 1.5-2 feet. It may be getting harder to find the right slope to trigger surface hoar, but it can't be completely ruled out yet.

    Where is it?  Wind-affected slopes are adding stress to the recently buried weak layers down 1-2 feet. Buried surface hoar continues to linger in mostly sheltered, shady slopes (facing NW-N-NE).  These layers are most likely triggered on slopes steeper than about 35 degrees. 

    How can you recognize it? Wind-affected slopes will have stiffer snow at the surface, keeping you from sinking deep into the snowpack. You may or may not experience snowpack collapsing and/or cracking while traveling. These red flags are obvious signs of instability. The surface hoar layer is subtle and may not "jump out at you" when searching for it in a snowpit (see photo here).     

    How can you manage it? You're most likely to trigger persistent slab avalanches involving either the shallowly buried facets/crust+facet combos on slopes steeper than about 35 degrees with stiff wind-blown snow or slabs. You can reduce the chances of tangling with surface hoar-driven avalanches by avoiding very steep (greater than about 35 degrees), shady (facing NW-N-NE) middle elevation slopes. 

    ADDITIONAL DISCUSSION: Recent moderate to strong NW winds have created dense slabs in exposed middle and upper elevations. You may find wind slabs near ridgelines, on the sides of gullies and chutes. Cracks shooting out from your skis or sled are an obvious sign of instability. Watch for drifts, dunes, and ripples on the snow surface. Wind slabs can have a smooth, chalky appearance and feel and sound hollow, like a drum. The easy move is to avoid obviously wind-loaded slopes steeper than about 35 degrees.

    (1/23/2023) Avalanche apparently triggered by a skier on Banner Summit. Slab depth and terrain characteristics are consistent with early January surface hoar layer. 7250', NNW. The date of this avalanche is uncertain, but likely occurred since Jan 18th. Photo taken Jan 23rd.

Avalanche Discussion

We can expect another round of sunny skies today. When the sun first hits fresh snow, it can cause loose avalanches to release. These small avalanches can rapidly load the recently buried weak layers below, causing larger slab avalanche to release. The most common locations for these avalanches are on sunny, steep slopes where rocky outcroppings exist. Avoid being on these slopes when you see avalanche activity or start to see signs of instability such as wet snow clumping up on your skis or roller balls. 

The surface hoar buried in early January continues to linger in this zone. The distribution of this layer seems isolated to mostly sheltered, middle elevations on slopes that face NW-N-NE .  There haven't been any reported avalanches on this layer in about three weeks, which tells me it's getting even hard to find slopes that are sensitive. While it is getting harder to find the right slope with larger surface hoar and steeper than about 35 degrees, it can't be completely ruled out yet. 

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