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

Even though deep slab avalanches have become more difficult to trigger and are now unlikely in most areas, they may remain possible in some specific terrain. The consequences of such an avalanche would still be dire. Some loose wet avalanche problems may also become possible today. These issues will keep the avalanche danger at MODERATE. 

Lawinenprobleme

  • Storm Slabs

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

    As the snow above the persistent weak layer has become stronger and as the persistent weak layer has started to adjust to the load above it, deep slab avalanches have become more difficult to trigger and are now unlikely in most areas. In some specific areas where the weak layer remains closer to the surface, triggering one of the avalanches may remain possible. These areas could include places where a shallower overall snowpack exists or areas where trigger points like rocks, cliffy areas, single trees, stumps, etc exist on slopes with a deeper snowpack. On these slopes, several tracks could exist before a person finds the trigger point that would release the entire slope. While the possibility of triggering one of these avalanches has decreased, the consequences of these deep slabs would still be very serious.

    Typical signs of instability do not usually accompany deep slabs. Often triggering a large avalanche represents the first sign of instability. Due to the uncertainty surrounding deep slab avalanches and the high consequences associated with them, making travel plans that focus on slopes where this problem is least likely to exist still represents a prudent choice. Lower angle northerly aspects still offer good recreation conditions.  

  • Loose Wet

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

    Loose wet instabilities will become possible on sun-exposed E-SE-S-SW-W aspects as the day warms up. Some loose wet instabilities could also form on northerly aspects if any rain falls on the existing snowpack or if cloud cover allows those aspects to warm up. Rollerballs, pinwheels, and small loose wet point releases should comprise most of the loose wet instabilities today, but a few larger loose wet avalanches may be possible. The amount of loose wet instability that forms today will depend on the mix of sun, cloud cover, wind, and precipitation that actually occurs.

Avalanche Discussion

* Snowpit tests targetting the facet layer buried 1 to 1.5 m deep in the snowpack yesterday on Silver Peak (north of Squaw) and Donner Peak (Donner Summit) indicated that triggering this layer has become more difficult, but that if it does break the resulting fracture could still propagate along the persistent weak layer. A snowpit on Waterhouse Peak (Luther Pass) also revealed this layer about 1 m below the surface.

* Other snowpit tests from across the forecast area earlier in the week showed more unstable results on this layer. Several natural and human-triggered deep slab avalanches occurred during and after the storm. 

* Loose wet instabilities including roller balls and pinwheels started occurring on sun-exposed slopes below 7500 ft. on Donner Peak and Silver Peak yesterday afternoon. Snow surfaces on all but the true north aspects above 7500 ft. started to become wet and sticky. 

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