Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
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Avalanche danger

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

Expect a patchwork of recently formed wind slabs on all aspects at upper elevations. In isolated areas, an avalanche starting in wind-deposited snow could break into deeper layers near the ground. Getting caught in even a small slide could have elevated consequences with exposed rocks and other obstacles in the runout.

Avalanche problems

  • Wind Slabs

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

    Over the past 48 hours, strong winds built unstable slabs on various aspects at higher elevations.  You can expect the distribution of wind slabs to expand throughout the day as the winds continue to transport snow into south-facing terrain. Wind slabs are typically found on the sheltered side of terrain features that block or re-direct winds. Be suspect of steep terrain features that encourage drifting, such as the leeward sides of ridgelines, alpine couloirs, gully features, and cross-loaded depressions. Shooting cracks and the sound of the snowpack collapsing under your weight are the best indications 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 near the ground, creating a larger avalanche involving the full depth of the snowpack.

  • Persistent Slabs

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

    Recent loading with new and wind-drifted snow has stressed persistent weak layers throughout the fragile early-season snowpack.  You are most likely to start an avalanche in terrain features prone to wind-loading which had continuous snow coverage in November and early December. If triggered, the resulting avalanche could break in unexpected ways involving the full depth of the snowpack. Early-season conditions may increase the likelihood of collisions with rocks, trees, and shallowly buried objects in the runout. Persistent slabs are slow to gain strength and can remain a concern over an extended period. Common strategies for managing persistent slabs include setting terrain margins to avoid areas where the problem might exist and waiting until more information becomes available or stability improves before approaching steep slopes.

    (12/24/2023)

    This avalanche failed on buried facets and likely ran on 12/21

    Photo: Clancy Nelson

Avalanche Discussion

Two wind slab avalanches were reported in the past 48 hours in the Mammoth Lakes area.

1/3/24:  A rider triggered a large wind-slab avalanche in Redcone bowl (~35 degrees, N aspect, 10,200'). The rider was above the start zone when the slab released and no one was caught or injured in the avalanche. Several other parties in the area at that time reported slope scale collapses and long shooting cracks in wind-deposited snow.

1/3/24: A small wind slab avalanche was reported in "Dave's Wave" (East aspect at 10,700') just outside the ski area boundary.

Despite the high degree of variability in snow depth across slopes and between drainages there is a general structure worth describing. In areas with more than a foot of snow, the base of the snowpack is composed of well-developed facets or depth hoar that formed in November. These weak grains are layered around decaying melt-freeze crusts and old thin wind slabs.  In areas sheltered from upper elevation winds, loose faceted snow and recent low-density snow make up the upper snowpack and the entire pack has a weak top-to-bottom structure with no discernable slab. In areas where the wind regularly strengthens the surface snow, intermittent snow storms in December and January have added 1 to 2ft of stronger snow over the persistent weak layers. This is the most concerning snow structure and continues to show itself with signs of instability and propagation in snowpit tests.

While the most recent storm has improved coverage in the Mammoth area, the general trend of thin early-season conditions remains. The consequences of a fall or avalanche accident could be more severe with ground, rocks and vegetation exposed at the bottom of slopes. Following another cold day today a winter storm moves into our area overnight with damaging winds. It may be worth including extra warm layers in your emergency gear and having a solid plan to self-rescue or shelter for an extened period if stranded in the backcountry.

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