Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Recent loading by snow and wind has built dense drifts and stressed buried weak layers. You can find sensitive wind slabs over a foot thick in leeward start zones. Avalanches could break in old snow involving the entire depth of the snowpack. Use extra caution near slopes steeper than about 30 degrees or in areas with exposure to overhead hazards.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2.5

    Recent loading has stressed weak layers of sugary snow buried 1 to 4 feet below the surface. Today, wind drifting will likely thicken slabs over weak snow. Persistent slab avalanches can be triggered from low-angle terrain below or adjacent to avalanche starting zones. You may not see trigger points like shallowly buried rocks until the snowpack collapses around you, sending shooting cracks across the slope. If triggered, the resulting avalanche could break with little warning, involving the full depth of the snowpack. Choose travel routes with lower slope angles and without exposure to overhead hazards.

    (1/17/2024)

    Profile of a trigger point for a slope scale collapse at 9,600' on a N aspect, in the Mammoth Lakes Basin. The persistent weak layer of Faceted grains bured on 1/2/24 is near the surface above the rock slab and drops deeper where the height of snow is over a meter. The snow was weaker in this area than on the wind-loaded slope I had just crossed. My weight broke into the weak layer and caused the whole slope to collapse.

    Photo: Everett Phillips

  • Wind Slabs

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

    As snowfall tapers this morning, gusty winds are forecast to remain at drifting speeds. Expect large drifts from yesterday and smaller, more sensitive slabs to form today in leeward terrain. Avoid dense, rounded, textured slabs on the downwind sides of ridgelines and the sidewalls of cross-loaded gullies. Watch for blowing snow and growing cornices. Shooting cracks and the sound of the snowpack collapsing under your weight are warning signs that wind slabs are unstable in your area. Keep in mind that even a relatively small wind slab avalanche breaking in the upper snowpack may be enough to step down to persistent weak layers, creating a larger avalanche.

    (1/20/2024)

    30 ft. long shooting crack in a soft wind slab. North aspect, near treeline terrain at 8850 ft.

    Photo: Clancy Nelson

Avalanche Discussion

Expect a break between storms during daylight hours. Avalanche problems will be more widespread in areas where the most new snow has fallen: in the Mammoth area and near the Sierra Crest. A wetter storm will increase the avalanche hazard tonight and tomorrow.

Yesterday, reports of small explosive-triggered wind slab avalanches and shooting cracks on leeward test slopes came from the Mammoth Lakes area. 

Wind slab avalanches can break today at the new/old interface where drifts formed over crusts and soft, settled snow. In sheltered terrain, small upsidedown storm slabs could break on the steepest slopes. A layer of small facets is buried 1 to 3 feet below the surface. Though these grains have been gaining strength, new loading may be enough to re-activate them. The biggest layer of concern consists of advanced facets and depth hoar buried near the ground down 2 to 4 feet. This layer has been responsible for continued reports of collapsing in the snowpack. Recent snow pit tests have confirmed that it can propagate a failure mid-slope, even on westerly aspects. The combination of new loading and the weak layers gaining strength is the source of some uncertainty and can make managing the persistent slab problem trickier. Variation in snow depth near and above the treeline has led to larger slabs with weaknesses at their margins and around trigger points in shallower areas.

Wider terrain margins are the antidote to uncertainty about snowpack stability.

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