Lawinenlagebericht

Central Sierra Nevada

Sierra Avalanche Center
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Lawinengefahr

Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Veraltet — dieser Lagebericht ist 10 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Considerable avalanche danger could exist today due to wind slabs and persistent slab avalanches.  Wind slabs could form on NW-N-NE-E-SE aspects near and above treeline at snow level and above.  Persistent slabs are possible on North aspects along the Sierra Crest and in the Mt. Rose area.  All other areas will have Moderate avalanche danger.  Dangerous avalanche conditions could exist today-large avalanches are possible in specific terrain areas.

Lawinenprobleme

  • Wind Slabs

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

    Winds slabs will become likely on NW-N-NE-E-SE aspects near and above treeline.  These wind slabs will only be possible at the snow level and above where new snow is accumulating.  Below this level, rain soaked snow and rain crusts will prevent most blowing snow from occurring and forming wind slabs.  Snow level could be anywhere from 8000-9500' or above today.  It is expected that late afternoon and into the evening for snow levels to drop.  Wind slabs will become possible at lower elevations if this occurs.

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

  • Deep Persistent Slabs

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

    Persistent slab avalanches are possible today on North aspects along the Sierra Crest above 8300' and in the Mt. Rose area above 9300' on slopes steeper than 32 degrees.  The faceted weak layer is buried anywhere from 1 to 3 feet deep near the base of the snowpack.  Recent observations targeting this faceted layer have showed mixed results through the forecast region.  Some observations have seen the facet layer gain strength with the recent warm temperatures and rain.  Other areas still show the potential for propagation to occur with additional load.  Today will bring a significant amount of additional weight on the snowpack with the possibility of 2 to 4'' of rain or up to several feet of wet heavy snow at the highest elevations.  There is some uncertainty as to what could occur with this persistent weak layer today.

    Large destructive avalanches are possible.  These avalanches could be natural or human triggered.  Any avalanches associated with this persistent slab would have large consequences.  Avalanche avoidance is recommended.  Avoid North aspects above 32 degrees in steepness.  Have a travel plan.  Pay close attention to run out zones, up tracks, and regrouping areas.   

Avalanche Discussion

Observations were made and received yesterday from Grouse Rocks (Ward Canyon area), Stevens Peak (Carson Pass area), and Tamarack Peak (Mt. Rose area).  In the Grouse Rock area, the recent rain is slowly percolating down and consolidating the snowpack.  Snow level was around 8400' with a sticky and wet upper snowpack.  No signs of instabilities or any blowing snow observed with the rain soaked surface snow. 

At Stevens Peak and Tamarack Peak, the rain has had less effect on the lower snowpack with some of these layers still dry snow.  Snowpack tests targeting faceted layers near the ground showed weakness in some areas that are consistent with previous observations.  On the East Ridge of Tamarack Peak, 9500', there was evidence of the facets gaining some strength and not being as reactive as before.  Evidence of rain was up to at least 9600' in the Tamarack Peak area and close to the top of Stevens Peak.  A breakable surface rain crust was encountered at both locations.  

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