Lawinenlagebericht

Central Sierra Nevada

Sierra Avalanche Center
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Lawinengefahr

Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

MODERATE avalanche danger exists in near and above treeline terrain where human-triggered wind slab avalanches are possible today. Deep slabs have become an unlikely but not impossible problem. 

Lawinenprobleme

  • Wind Slabs

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

    Strong winds and heavy snow left firm stubborn wind slabs on wind-loaded slopes in near and above treeline terrain. Additional snow today and tonight should form new smaller wind slabs on top of the existing wind slabs. Human-triggered wind slab avalanches will be possible today on NW-N-NE-E-SE aspects. While new wind slabs should remain small, avalanches involving the older harder wind slabs could be large and destructive. These older hard wind slabs should also be more difficult to trigger, but if they do break they may break after a person has fully committed to the slope.

    Recent wind slab avalanches, shooting cracks, cornices above slopes, firm hollow sounding snow, blowing snow, ripples, drifts, or other wind created textures can all help identify where wind slabs may exist. Use this information to avoid those slopes in favor of more sheltered terrain with softer snow or use lower angle slopes. 

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    3

    Deep slab avalanches that fail on the graupel/melt-freeze crust combination buried deep below the surface should continue become more difficult to trigger as the snowpack continues to settle and consolidate. This problem should be unlikely in most areas but it is not impossible in some isolated areas. East aspects above 9000 ft. in the Mt. Rose backcountry are the most suspect for deep slab activity, but some uncertainty still surrounds this problem. In the unlikely event that a deep slab avalanche were to occur today, it would be very large and likely unsurvivable. 

    Due to the combination of uncertainty and the catastrophic consequences of such an avalanche, deep slabs continue to warrant inclusion as an avalanche problem. Making backcountry travel plans that avoid slopes where unlikely but not impossible deep slab problems may exist remains the best choice for today.

Avalanche Discussion

* Natural wind slab avalanches triggered by large cornice collapses occurred on the far east ridge of Tamarack Peak (Mt. Rose backcountry) yesterday. Natural wind slab avalanches also occurred in near treeline terrain on Hidden Peak (near Emerald Bay), these also likely occurred yesterday morning and were likely triggered by cornice collapses.

* Evidence of widespread avalanche activity during the storm on Thursday was reported from Mt. Judah (Donner Summit area), Incline Lake Peak (Mt. Rose backcountry), Tamarack Peak (Mt. Rose backcountry), Relay Peak (Mt. Rose backcountry), Dicks Peak (Desolation Wilderness), and the Blue Lakes area (near Carson Pass).  Some of these were very large. They included wind slabs and deep slabs. 

* Snowpit observations targetting the graupel/crust layer near the crown of an avalanche on the Proletariat (Mt. Rose backcountry) yesterday still yielded unstable results on this layer. 

* Observations from Powderhouse Peak (near Luther Pass), Hidden Peak (near Emerald Bay), and Tamarack Peak (Mt. Rose backcountry) yesterday all showed continuous wind transport and firm stubborn wind slabs in near and above treeline terrain. They also found significant signs of settlement in the storm snow and no signs of instability below treeline.

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