Avalanche forecast

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Human-triggered avalanches involving layers of weak snow buried 1.5-2.5 feet down are possible. As increased winds and snowfall enter the area in the late afternoon, fresh slabs will begin to form along ridgelines and in exposed terrain. You can significantly reduce risk by steering clear of recently wind-affected terrain.

Avalanche problems

  • Persistent Slabs

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

    What is it? You'll find weak snow buried by late January and early February storms within the upper foot of the snow surface. In terrain that received recent wind-loading, a growing slab sits over these weak layers and is more sensitive. Buried 2-2.5 feet beneath the snow surface, you will find the layer of surface hoar that produced a handful of human-triggered avalanches in January (photo at right). 

    Where is it? You are most likely to encounter a reactive slab in terrain steeper than about 35 degrees where the wind has been building slabs on top of these weak layers. Look for these along ridgelines and near mid-slope terrain features like ribs and gullies. Buried surface hoar continues to linger in mostly sheltered, shady slopes (facing NW-N-NE) steeper than about 35 degrees.

    How can you recognize it?  Wind-loaded slopes have harder surfaces and a distinct appearance of pillows or lens-shaped slabs of snow. Cracks shooting out from your machine or skis clearly indicate an unstable slab. 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) mid-elevation slopes. 

    (1/23/2023) Persistent slab 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

Several layers of weak snow exist in the snowpack's upper 1-2.5 feet. In late January, a prominent surface hoar layer produced a handful of human-triggered avalanches in shaded, sheltered terrain. Snowpack tests and a lack of avalanche activity indicate that this layer is gaining strength, but surface hoar problems can linger for a long time. Newer weak layers buried in the upper foot of the snowpack generally lack the overlying slab necessary to produce avalanches. However, in terrain where the wind has been transporting snow, you may find slabs on top of these weak layers. Field observations and small triggered slides in neighboring zones indicate that these layers can produce avalanches when loaded with the right slab.

2-6 inches of snowfall and moderate winds are expected to arrive just before sunset. If the storm comes in earlier, look for active wind-loading. Pay attention to increasing wind transporting snow and creating fresh slabs over older ones. These slabs are likely small but can add stress to the weak layers mentioned in Avalanche Problem #1. 

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