Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

Dangerous avalanche conditions will continue today.  New snow and high winds have loaded existing weak layers in our snowpack.  Large avalanches are the main concern today failing well below our recent storm snow.  High winds will also continue to create slabs of wind blown snow in exposed areas.  Cautious route finding with large safety margins will be required to help avoid todays avalanche problems.  

Avalanche problems

  • Persistent Slabs

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

    The recent storm has reloaded the Jan 2 persistent weak layer-where buried surface hoar or weak snow near crusts exists.  This layer is buried 1 to 3 feet below the snow surface in wind sheltered areas.  During our last 2 storms this past week, avalanches have occurred on this weak layer and that is expected to continue today.  Avalanches that occur on this weak layer in wind blown areas could be much deeper and larger in size.

    Recent avalanches, snow surface cracking, snowpack collapse, or whumpfing sounds will indicate unstable persistent slabs.   These avalanches could be remotely triggered from above, below, or from off to the side of a slope.  A sunny powder day will be tempting for many of us to push into steeper terrain.  Today is not that day-our snowpack needs some time to adjust to the new snow load on these weak layers.  Avoid steep terrain and runout areas below steep slopes where this avalanche problem exists.

    (1/10/2024)

    When I stepped on the trigger point, I heard a noise like a distant shot and felt the slope collapse in a 50' diameter around me. Shooting cracks also propogated across the entire slope. The failure layer was surface hoar on a crust about 15-18 inches below the surface (Jan 2 PWL, surface hoar).

    Photo: SAC

  • Wind Slabs

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

    Gale force SW/W winds yesterday have built out cornices and wind slabs in exposed areas.  Winds have shifted overnight and are expected to be strong from the NW through today continuing snow transport.  Human triggering of these wind slabs will be possible through today.

    Look for areas where blowing snow is depositing and for any areas of snow surface cracking.  Clues such as recent avalanches, built out cornices, wind drifts, and loaded vs scoured snow surface conditions can help identify the areas of greatest concern. Exercise increased caution today around and below steep wind loaded areas. 

    (1/8/2024)

    NE face of Elephants Back, wind slab avalanche center right.  Carson Pass area.

Avalanche Discussion

Our thoughts and condolences are with all the people involved in the Palisades Tahoe avalanche that happened on Wednesday January 10.  Since this avalanche occurred within the ski resort boundary, no additional information is available from the Sierra Avalanche Center.  Please visit www.avalanche.org for an accident report.

 

More on our persistent slab avalanche problem:

The surface hoar and weak snow near crusts buried on Jan 2 have become the most problematic layers in our snowpack. In sheltered areas, these are buried 1-3 ft below the snow surface.  They could be much deeper in places, especially where wind-loaded snow exists above them.  There have been many avalanches reported, both human triggered and natural, on these weak layers over the last week.

For much of the season, the persistent slab problem focused on faceted snow near the base of the snowpack. Substantial strength gains in the midpack and a deepening of the snowpack along the Sierra Crest have reduced concerns for deep weak layer failure until a major atmospheric river type storm with multiple inches of SWE returns to the forecast area. The eastern side of the forecast area, where a weaker and shallower snowpack exists, has a greater concern for future additional loading.

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