Lawinenlagebericht

Central Sierra Nevada

Sierra Avalanche Center
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Lawinengefahr

Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

Moderate avalanche danger exists throughout the forecast area due to wind slabs and persistent slab problems.  Wind slabs are possible on NW-N-NE-E-SE aspects near and above treeline at elevations above 8500'.  Persistent slabs are possible on North aspects along the Sierra Crest and in the Mt. Rose area.  Avalanche danger is expected to rise as another storm impacts our region tonight and through Saturday.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1

    SW winds have been in the strong to gale force range overnight at higher elevations and will continue through today ahead of our next approaching storm.  Wind slabs will be possible on NW-N-NE-E-SE aspects near and above treeline at elevations above 8500'.  Below around 8500', rain soaked surface snow will prevent most blowing snow from occurring.  These wind slabs are expected to occur on slopes steeper than 37 degrees. 

    Look for blowing snow, cornice formation, snow surface scouring and wind pillows as clues to where wind slabs may be forming.   

  • Deep Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2

    Recent snowpack tests and observations continue to show weakness on a faceted layer buried 1 to 3 feet deep near the base of the snowpack.  We have a slight break in the weather today before another storm system will impact the region tonight and tomorrow.  Snowpack tests are indicating it will be possible for this weak layer to fail and cause avalanches with additional load.  This weak layer is found on North aspects along the Sierra Crest above about 8300' and in the Mt. Rose area above about 9300'. 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 and informal observations may not supply much useful information.  Evaluate and select terrain carefully.  Avoid run out zones and pay attention to locations of up tracks and regrouping areas.

     

Avalanche Discussion

Observations from Andesite Peak (Donner Summit area) and Blue Lakes (Carson Pass area) both showed warm temperatures and rain soaked surface snow at elevations below 8500'.   New snow amounts were limited to 4 to 6'' of mostly wet rain saturated snow.  No signs of instabilities were observed at these locations.

Observations from Tamarack Peak (Mt. Rose area) showed 6 to 8'' of new snow in this area at elevations above around 9000'.  Blowing snow was observed with small dense wind slabs forming along ridges.  Wind slabs were sensitive enough to be intentionally triggered by a skier.  Snowpit observations targeting the buried facet layer continued to show weakness.  Snowpack tests showed that propagation was possible along this weak layer and that the additional recent storm load may be starting to overload the weak layer.

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