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 11 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

CONSIDERABLE avalanche danger exists on all aspects and elevations on slopes steeper than 35 degrees due to a combination of wet snow instabilities caused by rain on snow and newly formed wind slabs at the upper elevations. Human triggered loose wet avalanches and wind slab avalanches are likely today and some isolated wet slab avalanches may be possible. People traveling in the backcountry should make careful snowpack evaluations, use cautious route-finding and conservative decision-making, and expect to get very wet.

Lawinenprobleme

  • Loose Wet

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

    Widespread rain on snow will cause wet snow instabilities to form on all aspects on slopes steeper than 35 degrees below 9600 ft. Loose wet point releases, roller balls and pinwheels should represent the majority of these wet snow instabilities and could entrain enough snow to carry a person down a slope. Terrain traps like gullies, cliffs, creeks, etc. would magnify the consequences of these loose wet avalanches and could allow for them to bury or injure a person. Human triggered loose wet avalanches are likely today and natural loose wet avalanches are possible. While loose wet avalanches will comprise the majority of wet snow instabilities, some wet slab avalanches may also be possible in isolated areas that receive the most rain. While the danger posed by these wet snow instabilities will increase as more rain impacts the forecast area today, it will quickly decrease as the snow levels drop this evening and tonight. 

  • Wind Slabs

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

    Strong winds will allow wind slabs to form on wind loaded N-NE-E and cross loaded NW and SE aspects on the upper elevation near and above treeline slopes. Since snow level should remain high today these wind slabs should remain limited to terrain above 8000 to 8500 ft. where more of the precipitation falls as snow. At these upper elevations human triggering of heavy wind slabs will become likely today and some natural wind slab avalanches may become possible. These wind slabs will become larger, more widespread, and move down in elevation as the snow levels drop this afternoon and tonight. Use clues like blowing snow, cornices above a slope, wind drifted snow, ripples in the snow, and other wind created textures to help identify where wind slabs have formed.  

Avalanche Discussion

Yesterday observations from Tamarack Peak, Incline Lake Peak (both in the Mt. Rose backcountry), and Round Top (Carson Pass) all found a well consolidated snowpack with very few signs of instabilities. On Round Top some small skier triggered loose dry sluffs did occur and some small wind slabs had started to form near ridgelines on Tamarack Peak during the afternoon. Neither of these small instabilities represented much of a problem for backcountry travelers yesterday. 

What happened to the deep persistent weak layer?

In early to mid January, up to 3 separate surface hoar layers formed and were buried by subsequent storms on N-NE-E aspects near treeline and below treeline. A widespread persistent slab avalanche cycle occurred Jan 5 through Jan 19 on these weak layers.  Many slopes have been "cleaned out" by already avalanching, or the surface hoar has been collapsed or compressed and has gained strength.  Targeted observations and snowpack tests have shown that these layers, in the majority of locations, are no longer reactive and have assimilated into the snowpack.  No avalanche activity has been associated with these buried surface hoar layers since Jan. 19.

This deep persistent avalanche problem has become unlikely and has been removed as an avalanche problem.

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