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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Kernpunkte

CONSIDERABLE avalanche danger will exist today due to a combination of loose wet, deep slab, and wind slab avalanche problems.  A moderate to strong atmospheric river storm will bring widespread rain and high elevation snow throughout the forecast area over the next couple days.  Dangerous avalanche conditions will exist with natural and human triggered avalanches expected.

Lawinenprobleme

  • Loose Wet

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

    Widespread rain today and tonight will make loose wet avalanches likely on all aspects and elevations.  Rain is forecasted up to 8000-8500' today and could fluctuate throughout the storm.  Many of the wet instabilities should be in the form of roller balls and pinwheels with larger loose wet avalanches capable of injuring and/or burying a backcountry user possible.

    Avoid steep terrain that is being rained on.  Roller balls and pinwheels will be an indication that the surface snow is loosing strength and that larger loose wet avalanches could occur.

  • Storm Slabs

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

    A layer of graupel was deposited on top of a melt freeze crust before our last storm that has resulted in 4 deep slab avalanches-3 naturals and 1 remotely skier triggered avalanche on last Sunday.  This graupel/melt freeze crust combo is buried 3 to 5' deep and continues to show some reactivity and unstable snowpack test results.  This layer has been found in other areas within the forecast region but all known avalanche activity has been located in the Mt. Rose area.  All deep slab avalanches have been around 9000' and above and on East aspects.  As a large load impacts our area today and tomorrow, this layer could fail causing large and destructive avalanches.  These deep slabs will be possible on NE-E-SE aspects near and above 9000'.

    The only effective deep slab management strategy is avoidance-staying off aspects of concern, using slopes under 30 degrees on aspects of concern, and avoiding connected terrain where remote triggering could occur.  Any avalanches associated with this weak layer would be large and have severe consequences. 

  • Wind Slabs

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

    Gale force S/SW winds with high elevation snow will form wind slabs on NW-N-NE-E-SE aspects in near and above treeline terrain.  These wind slabs are expected to form above 8500' where snow is forecasted with no wind slabs expected below 8000' where mostly rain is forecasted.  Fluctuations in the snow level may increase or decrease this avalanche problem greatly depending on how much available snow there will be for wind transport.  Expected rain may also weaken recently built out cornices from the last storm causing them to fail downslope.

    Look for blowing snow, cornice formation, and forming wind pillows.  Avoid steep wind loaded terrain and run out zones below cornices.

Avalanche Discussion

* A large whumpf was felt on Proletariat Bowl (Mt. Rose area) while investigating a recent deep slab avalanche.  This deep slab occurred over the weekend and had the same characteristics as the other deep slab avalanches that have occurred in the Mt. Rose area - layer of graupel on top of a melt freeze crust that was buried before our last storm.  Snowpack tests continued to show some unstable test results in this area.

* Wind transport was occurring at Twin Lakes ( Carson Pass area) with poor bonding of the old snow surface to the new wind transported snow.  Moderate blowing snow was also observed at Echo Summit area.

*  The graupel/melt freeze crust combo was observed on Hidden Peak (West Shore area) at 8880' on an E aspect.  Snowpack tests in this area showed no unstable test results. 

 

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