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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Veraltet — dieser Lagebericht ist 6 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Slab avalanches 1 to 3 ft deep that break on a weak layer of buried surface hoar remain possible at all elevations today. New snow and wind may also form fresh slabs of wind drifted snow in some areas. These wind slabs could step down to break on the persistent weak layer. Choosing conservative terrain can help avoid getting caught by a persistent slab problem that is unusual for this area. MODERATE avalanche danger will continue.

Lawinenprobleme

  • Deep Persistent Slabs

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

    While no new avalanches were reported to have occurred yesterday, people have triggered persistent slab avalanches every other day since March 25. New snow will not help solve this problem. Slab avalanches that fail on weak snow (surface hoar on top of a thin crust) buried below the recent snow still remain possible today. In sheltered areas, people have triggered avalanches about 1 ft deep. In more exposed areas where slabs of wind drifted snow exist above this layer, the avalanches have measured 2 to 3 feet in depth. These avalanches have propagated long distances across slopes and wrapped around terrain features. In some cases, people triggered them from a distance while traveling in lower angle terrain connected to steeper slopes.

    Open areas on NW-N-NE aspects at all elevations represent the most likely places to find this persistent slab problem. Avalanches could fail mid-slope or at the top of a slope. They could break above or behind the person who triggers them with very wide propagation or be remotely triggered. Identify slopes where persistent slabs could exist. Manage your aspects and slope angles carefully and be careful with terrain to connected to steeper slopes. 

    Plenty of great snow exists on lower angle more sheltered terrain. Choosing these areas will help find excellent recreation conditions and avoid potential wind slab or persistent slab avalanches.

  • Wind Slabs

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

    Unstable slabs of wind drifted snow may also still linger on wind-loaded and cross-loaded NW-N-NE-E-SE aspects. New snow and wind last night and today will create new wind slabs near some ridgelines. These fresh wind slabs should remain small in most places. They should also be easier to trigger and could step down to the buried surface hoar or graupel layer. In those cases, they would behave as the persistent slabs mentioned above. Human triggered wind slab avalanches remain possible today.

    Look for built out cornices, wind pillows, and steep wind loaded terrain where unstable wind slabs are most likely to exist. Wind slab avalanches have been propagating wider than normal. Avoid areas below large cornices and wind loaded slopes.

Avalanche Discussion

No new avalanches were reported yesterday, but more reports of previous activity came in in the form of skier triggered avalanches on Tallac on Friday and snowmobiler avalanches above Frog Lake near Castle Peak on Thursday. Both of these avalanches failed at the base of the recent snow about 1 ft below the surface where buried surface hoar and graupel have been observed on top of a thin crust.

Observations from upper elevations on Tallac yesterday did not find as many signs of instability.

In the Mt. Rose backcountry yesterday, observations revealed less recent snow and less of a crust at the base of the recent snow. Tests targeting this interface provided variable results with fewer signs of instability. No persistent slab avalanches had been reported in the Mt. Rose area.

Observers continue to report soft cold snow on northerly aspects. In areas exposed to sunshine, breakable crusts existed with wet sticky snow forming on some sun-exposed southerly aspects yesterday. 

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