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

Last night's snow surface refreeze is expected to be relatively weak. Rapid warming conditions early this morning will quickly create the possibility of loose wet snow avalanches at all elevations today. Cornice fall is also a possibility. MODERATE avalanche danger will form rapidly at all elevations once the surface crust melts away, exposing areas of deep wet snow.

Lawinenprobleme

  • Loose Wet

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

    A relatively weak snow surface refreeze is expected to have occurred last night. Overnight air temperatures were well above freezing in most locations at the mid and upper elevations. Snow surface refreeze last night was entirely dependent on radiational cooling of the snowpack under clear skies. The relatively strongest refreeze will have occurred on open slopes. A poor refreeze is expected to have occurred under forest canopy. Rapid warming and surface melt will occur today starting right from sunrise. The surface crust will melt away rapidly today, exposing deep wet snow, and opening the door for loose wet snow avalanches this morning. A loose wet avalanche problem is expected to form quickly today on all aspects at all elevations. Avalanche size is expected at D1 to D2, depending on what the terrain is capable of producing.

    Avoid travel in avalanche terrain on slopes where marginally supportable to unsupportable deep wet snow exists. Today's winds may create some cooling and slow melt rates this morning directly along the ridgetops, but not mid slope or below.

  • Glide Cracks

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

    A weak overnight refreeze and rapid warming conditions today may fuel additional cornice fall. Large to very large cornice chunks falling onto the slopes below have destructive potential on their own. If the cornice fall triggers a loose wet or wet slab avalanche on the slope below the destructive potential will be even greater.

    Stay well back from abrupt edges along ridgetops and stay out from under any cornices above you. Cornices where you can hear or see dripping water are weakening and could be nearing collapse.

     Photo: Natural cornice fall that triggered a slab avalanche yesterday on Ralston Pk (Echo Summit area).

Avalanche Discussion

* Diurnal melt-freeze conditions exist on all aspects.

* Observations made yesterday on Rubicon Peak (West Shore Tahoe area) and on Ralston and Echo Peaks (Echo Summit area) revealed a decent snow surface refreeze had occurred the night before. The surface crust had weakened substantially from melt by the late morning hours.

* A natural cornice collapse occurred just before noon yesterday at around 9,100' on the E aspect of Ralston Peak (Echo Summit area), triggering a size D2 slab avalanche on the slope below.

* Signs of layer consolidation from recent melt and rain have been observed in the top few feet of the snowpack on all aspects, minimizing the concerns for additional wet slab avalanches. Cornice fall may still be able to trigger a very isolated wet slab avalanche.

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