Lawinenlagebericht

Central Sierra Nevada

Sierra Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

Unsettled weather will continue for our region with large storms in the forecast over the next week.  Additional new snow today with high winds will create slabs of wind blown snow in wind exposed areas. Unstable snow may continue to exist on steep slopes in wind protected areas.  If you see signs of instability today, change plans to easier to manage terrain away from avalanche slopes .

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2–3

    Additional snow and gale force SW winds will continue to build and add on to existing wind slabs on NW-N-NE-E-SE aspects in near and above treeline areas.  Large to very large wind slab avalanches along with cornice collapses could occur again today.  The most likely area for these wind slabs will be below ridges and in gully features where wind blown snow can accumulate.   In some isolated areas, these wind slabs could be on top of a layer of buried surface hoar or near surface facets which would cause large and wide propagating avalanches. 

    Look for blowing snow, large cornices above a slope, and wind textured snow surfaces as clues to where wind slabs have been forming.  Plan routes around steep wind loaded terrain and avoid slopes below large cornices. 

    (12/28/2022)

    Natural wind slab avalanche on Elephants Hump R3D3.  Possible cornice fall trigger failing on a mixed layer of small facets and surface hoar just below the new/old interface

    Photo: Travis Feist

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Colder temperatures overnight will help to refreeze some of the rain soaked snow that exists in our upper snowpack from our last storm.  An additional up to 5'' of snow is expected this morning.  While most of the bonding of the upper snowpack is expected to improve, there are a couple concerns.  Layers of graupel exist in the recent storm snow that have shown planar test results in some areas.  In isolated locations, buried surface hoar and/or near surface facets may continue to exist under our recent storm snow.  Temperatures are expected to increase later today as the next storm arrives tonight with snow levels rising up to 7000-8000'.  Wet snow instabilities will begin to occur as temperatures increase and rain begins to fall on new snow.

    Look for signs of instability while traveling in the backcountry.  Recent avalanche activity, shooting cracks, collapsing, and rapid warming.  If you see signs of instability, move away from avalanche terrain into less steep and easier to manage terrain.

Avalanche Discussion

  • Multiple large to very large natural wind slab avalanches occurred at the end of the last storm cycle.  Some of these failed on buried surface hoar and/or near surface facets.
  • Cornices remained fragile and weak yesterday. 
  • Rain during the storm and warm weather before the storm likely destroyed most of the shallowly buried surface hoar that existed on NW-N-NE aspects. It may still linger in a few isolated areas above 8,000 ft to 10,000 ft.

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