Avalanche forecast

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Avalanche danger

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

Conditions are dangerous at upper elevations. Natural avalanches are possible in windy terrain. Expect to trigger large, 1-3 foot thick avalanches where the wind has drifted snow or stiffened the snow surface. Similar slides are possible in terrain more sheltered from the wind—especially in the Smokys and in the mountains surrounding Galena Summit. Avalanches may be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes.

Avalanche problems

  • Wind Slabs

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

    Expect to find sensitive slabs in wind-loaded terrain. Tuesday, Ben observed a large avalanche on the north side of Copper Mtn near Banner Summit (report). The slide was triggered remotely from low-angle terrain and released on a wind-loaded slope just below the ridge. You could trigger similar avalanches today as an uptick in wind forms a fresh batch of wind slabs this afternoon.

    Slabs will be thicker, wider, and more dangerous at windier, upper elevations. Look for them near ridgelines and along mid-slope terrain features like ribs and gullies. Stiff slabs may extend into wind-exposed middle elevation terrain. Some wind slabs sit atop weak snow (facets, surface hoar, crusts), which may make them more sensitive to triggering and could cause them to break wider than expected.

    Snowpack collapsing or cracks shooting from your skis or sled are obvious signs of instability. Low density snowfall and shifting, intermittent wind may mask the usual clues that the wind has been at work. This may make it difficult to identify a recently wind loaded slope from a distance. Even subtle wind affect over the past ten days may be enough to stiffen the snow and increase your odds of triggering a slide.

    (3/1/2023) This small wind slab avalanche was triggered near the top of The Cross on Galena Summit. Small wind slabs like these can act as triggers for larger persistent slab avalanches.

  • Persistent Slabs

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

    You could trigger 1-3' thick avalanches on buried weak layers. This scenario is most likely in the Smokys and in the mountains surrounding Galena Summit. The weight of recent storm snow is overloading these layers, which include: sugary facets, crusts, or crust + facet combinations. These slides are possible in both obviously wind-loaded and sheltered terrain (photo above/right). Today's storm may release wind slab avalanches, cornices, or sluffs that can act as triggers stepping down to these weak layers to produce a large, dangerous slide. 

    Middle and upper elevation slopes are the most dangerous because more snow fell there in the past few days. Weak layers of snow exist below the recent storm snow and deeper in the snowpack (photo). The distribution, character, and sensitivity of these layers vary from slope to slope, and stability tests are of limited use. Your best bet is to assume this problem exists until proven otherwise. 

    Persistent slab avalanches behave in unpredictable ways. You can trigger them from a distance, from gentle terrain above, below, or to the sides of steep slopes. These slides may break wider than expected or higher on the slope above you. The first skier or rider may not trigger an avalanche on an unstable slope. Do not assume tracks mean a slope is safe. You can reduce your risk by avoiding slopes steeper than about 35 degrees—especially large avalanche paths and those with ugly consequences if you are caught in a slide. 

    ADDITIONAL DISCUSSION: Triggering a very large persistent slab avalanche on weak, sugary facets buried deeper in the snowpack would take some bad luck. However, this unlikely scenario cannot be ruled out in rocky, wind-swept areas with variable snowpack depths of less than about 2 feet. This setup is more common in the Pioneer, Boulder, and White Cloud Mountains.

    (3/1/2023) This large avalanche released above the E Fork of the Big Wood on a NW aspect at 8,600'. The slab initiated in wind-loaded terrain and appears to have failed on a weak layer buried by snowfall since Sunday (2/26).

Avalanche Discussion

Today's storm will build another fresh batch of sensitive drifts and slabs. Many slopes may be teetering on the edge, and this added load is likely to produce natural avalanches. Small wind slab avalanches, cornice failures, and sluffs may be dangerous in their own right but can also act as triggers stepping down to release a large, dangerous, persistent slab avalanche.  

Several inches of recent snowfall built a slab atop a variety of weak layers in the upper 3' of the snowpack. The distribution, character, and sensitivity of these layers vary across zones and from slope to slope but it's safe to say one or more of these layers exist. The sensitivity of these layers is proven by large natural and human-triggered avalanches from Banner Summit (report) to the White Clouds (photo) and south into the Wood River Valley (report). Each of the recent skier-triggered slides were triggered from a distance. Yesterday a skier triggered this slab avalanche near Hailey as they crossed the bottom of the slope (report). Last night, this avalanche was triggered from flat terrain near Greenhorn (photo). 

Many slopes have most of the ingredients for an avalanche, plenty of new snow and a weak layer, but lack a cohesive (stronger) slab to propagate a failure and release a slide. It doesn't take much to change this picture. This morning's sun, the settling of the storm snow overnight, or today's wind-loading can all add to the slab's strength and increase the odds of natural and triggered slides. 

Today is a good day to choose conservative terrain, keep your slope angles low, and anticipate the possibility of triggering a slide from below, above, or to the sides of a steep slope. Keep overhead hazard in mind as wind speeds pick up this afternoon. 

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