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

Considerable avalanche danger exists as additional loading of snow and rain occur throughout the region.  Wind slabs will be possible on NW-N-NE-E-SE aspects near and above treeline.  Storm slabs will be possible on all aspects below treeline and near treeline where previous snow coverage existed.  Persistent slab avalanches will become possible on N aspects along the Sierra Crest and in the Mt. Rose area.  Dangerous avalanche conditions exist.  Careful snowpack evaluation, cautious route finding, and conservative decision making are essential.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    Strong to gale force SW winds and new snow will make it possible for wind slabs to form throughout today.  Wind slabs could exist on NW-N-NE-E-SE aspects near and above treeline.  These wind slabs will be possible on slopes steeper than 37 degrees.  As warming occurs throughout the day, it will further the problem that these wind slabs will be much more dense than the underlying snow beneath.

    Look for clues for wind slab development such as blowing snow, cornice formation, and wind pillows.  Avoid slopes with active wind loading.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    Storm slabs will develop on all aspects in below treeline and near treeline terrain on slopes steeper than 37 degrees.  New snow followed by a warm transition sometime today will make an upside down new snow layer with the heavy dense snow on top and lighter snow beneath.  Rain level is forecasted to rise up to at least 8000' by this afternoon.  Depending on how high it rains and amounts, avalanches could have wet slab and wet loose avalanche characteristics.

    Most slopes with enough previous snow for travel will have this avalanche problem through today.  It should be easy to feel or see any large density changes within the new storm snow. Cracking around skis, shooting cracks, and rain on new snow will all be red flags and show that there is cohesion in this new storm slab layer.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Persistent slab avalanches will become possible today as heavy loading of snow and rain occurs to the snowpack.  The potential weak layer is faceted snow that exists near the base of the snowpack usually on top of a ground level ice layer.  This weak layer is found on North aspects along the Sierra Crest above about 8300' and in the Mt. Rose area above about 9300'.  The faceted layer is buried anywhere from 1 to 3 feet deep in the snowpack.  Slopes 32 degrees and steeper are the main concern for this avalanche problem.

    Any avalanche activity associated with this persistent slab problem would have large consequences.  These avalanches could be remotely triggered from connected terrain.  Informal observations may not supply much useful information.  Advanced terrain management skills are needed today to safely navigate and avoid this avalanche problem.

     

     

Avalanche Discussion

Observations made on Relay Peak and Tamarack Peak (Mt. Rose area) continue to show ongoing concerns for a potential persistent slab avalanche problem.  Snowpack tests at several different aspects, elevations, and locations showed that the main concern are north aspects above 9300' in the Mt. Rose area.  Similar snowpack layering existed with a weak faceted layer of snow buried near the base of the snowpack just above a basal ice layer.  This faceted layer was showing failure with PST's that indicated propagation was possible.

Regions covered