Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

Dangerous avalanche conditions still exist and large, deep, destructive human-triggered avalanches remain likely due to deep slabs and wind slabs. CONSIDERABLE avalanche danger exists at all elevations. This danger rating is when the most avalanche fatalities occur. Carefully evaluate the snowpack and terrain and use this information to create safe and conservative travel plans. Avoid areas where avalanche problems may exist. The avalanche danger will rise to HIGH again tonight as more snow and wind impact the forecast area.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    New snow and continued gale-force winds today will create wind slabs on top of the refreezing snowpack. These wind slabs will form in typical leeward areas in near and above treeline terrain and could extend onto open slopes in below treeline terrain as well due to the strength of the winds. Human triggered wind slab avalanches will be likely today and natural wind slab avalanches will be possible. As snowfall intensity increases tonight natural and human triggered wind slabs will become likely to very likely again. Wind slabs could exist on wind loaded NW-N-NE-E-SE aspects at all elevations and could step down to the deep slabs mentioned below. 

    Use clues like blowing snow, cornices, drifts, wind-created surface textures and other evidence of wind transport to identify where wind slabs exist and avoid them. 

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    3

    Human triggered deep slab avalanches that fail on the facets near the 12/15 rain crust will be likely today and natural deep slabs may remain possible on W-NW-N-NE-E aspects at all elevations. This problem will linger until the snowpack has had time to refreeze and gain some strength. This refreezing process does not happen overnight and could take a few days for the cold temperatures to permeate through the snowpack. Any of these avalanches that do occur would be large, very deep, and destructive. They could also run much farther than expected and involve snow that is still wet from yesterday.

    Deep slabs are unpredictable and traditional observations do not provide reliable data about them. Sometimes the first sign of instability is a deep slab avalanche even on a tree-covered slope or a slope with tracks on it. Remote triggering with large propagation into any connected terrain remains possible. Avoiding any terrain where this problem might exist represents the wisest choice for today. Deep slabs can occur on less steep slopes and any slopes steeper than 30 degrees are suspect. 

Avalanche Discussion

Yesterday observations on Carson Pass revealed widespread wet deep slab avalanches, deep wet wind slab avalanches, loose wet avalanches on N-NE-E-SE aspects. Many of the slab avalanches had crowns in the 4 to 7 ft. range and looked to have failed naturally due to rain loading the snowpack and causing the facets near the 12/15 rain crust to break. Some avalanches broke higher in the snowpack. These avalanches looked to have occurred during the night on Saturday night or on Sunday morning. The avalanches occurred in below treeline, near treeline, and above treeline terrain and on small slopes tucked into tree-covered areas as well as on large open slopes. 

Regions covered