Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Wind drifted snow that has formed into slabs remains an avalanche problem today above treeline and near treeline. A persistent weak layer of crust and sugary faceted snow is keeping isolated instability and a pesky low likelihood high consequence avalanche problem ongoing near treeline and below treeline. Avalanche danger is MODERATE for all elevations.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Small unstable wind slabs were observed yesterday above treeline. Instability of these slabs of wind drifted snow may linger today. In isolated areas, these wind slabs are on top of surface hoar which may slow the rate of stabilization. The areas of concern for this avalanche problem are near treeline and above treeline on NW-N-NE-E-SE aspects. Avalanche size is expected at D1 to D2. A period of larger wind slab formation will occur tonight with SW wind and new snowfall.

    Identify slopes where unstable wind slabs may exist. Use clues such as cornice formations, wind pillows, scouring vs deposition patterns on ridgelines, and areas of snow surface cracking to highlight areas of concern. Communicate within your group a plan for how to move around these areas with caution.

     

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    It would be nice to be done worrying about this avalanche problem, but we're just not there yet. Isolated instability is observed somewhere daily below treeline and near treeline on NW-N-NE-E aspects on the sugary Jan 4 crust/facet persistent weak layer. In most below treeline locations, this weak layer is buried 1 to 2 feet below the snow surface and as much as to 8 feet below the surface near treeline under wind drifted snow. Human triggered avalanches size D2 to D3 have become unlikely on a regional scale, but an isolated avalanche is still a concern. Tonight's rain/snow loading event could make this weak layer more reactive.

    A low likelihood high consequence avalanche problem is what remains at this time. Spatial variability of stable vs unstable is increasing. Many areas are stable, others are not. Make conservative terrain and route selections in any areas where unstable snowpit test results or other signs of instability exist.

Avalanche Discussion

* Small shallow unstable wind slabs were observed yesterday above treeline in the Carson Pass area on Elephants Back and Red Lake Peak. On Red Lake Peak, skier triggered cracking was observed in wind drifted areas. Looking under these wind slabs revealed that they were on top of surface hoar.

* Surface hoar under wind slabs above about 8,500' that was observed yesterday on Carson Pass may exist in the Luther Pass and Echo Summit areas where surface hoar was observed on Thursday. This was not seen yesterday in the Mount Rose or West Shore Tahoe areas. The presence or absence of surface hoar in other above 8,500' areas is unknown.

* Snowpit tests targeting the persistent Jan 4 crust/facet layer continue to show spatial variability. Unstable test results were reported yesterday from Red Lake Peak (Carson Pass area). Some mixed results were reported yesterday from Scout Peak (Echo Summit area). No persistent slab instability was reported yesterday from Tamarack Peak (Mount Rose area) or from Rubicon Peak (West Shore Tahoe area). Comparing the unstable results from Jan 23 on Stoney Ridge with the lack of instability observed yesterday on adjacent Rubicon Peak demonstrates the spatial variability quite well.

Regions covered