Lawinenlagebericht

Central Sierra Nevada

Sierra Avalanche Center
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Lawinengefahr

Hochgebirge
2 · Mässig
Waldgrenze
1 · Gering
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 11 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

MODERATE avalanche danger is expected today above treeline on SE-S-SW-W-NW aspects on slopes 35 degrees and steeper in areas where new wind slabs form this morning. For all other areas, LOW avalanche danger exists. Normal caution is advised. Very isolated deep persistent slab avalanches are unlikely but not impossible in open near treeline and below treeline areas on N-NE-E aspects on slopes 32 degrees and steeper.

Lawinenprobleme

  • Wind Slabs

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

    As NE winds increase this morning, redistribution of snow on the ground is expected in above treeline areas. Visible blowing snow, wind loading, and new wind slab formation is expected today above treeline on SE-S-SW-W-NW aspects. New wind slab size is expected to be fairly small, but could reach sufficient size to bury or injure a person if avalanche activity were to occur in the most efficiently wind loaded areas. Use clues such as blowing snow, new cornice formation, wind pillows, and snow surface texture to identify suspect slopes.

  • Storm Slabs

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

    Deep persistent slabs have become an unlikely but not impossible avalanche problem. Areas where weak buried surface hoar layers exist 1.5 to 4.5 feet deep in the snowpack and remain in an unstable, reactive state are becoming increasingly isolated. A widespread persistent slab avalanche cycle occurred Jan 5 through 19 as these weak layers collapsed. As time has passed, distribution of these problematic weak layers has been changing. In some areas, avalanche activity has cleaned them out. In some areas they have already collapsed or been compressed and are no longer reactive. In other areas the buried surface hoar crystals are rounding and gaining strength. However, in some areas snowpit data continues to point to ongoing instability.

    Even though avalanche occurrence is unlikely, consequences remain high. Due to the depth of the weak layer and density of the snow above, any deep persistent slab avalanches that do occur could be large, destructive, and difficult to survive. Open areas near treeline and below treeline on N-NE-E aspects is where this avalanche problem is found, not up near the ridgetops in the traditional avalanche start zones. This is the type of avalanche problem where a slope could avalanche after it has already been traveled by numerous individuals. For more info on managing deep persistent slabs, see the Avalanche Problems Toolbox.

Avalanche Discussion

Observations were made and received yesterday from Incline Lake Peak and Mt. Baldy (Mount Rose area), Silver Peak (Pole Creek area), Mt. Tallac (Desolation Wilderness area), and Trimmer Peak (Luther Pass area). Along the ridgelines, wind slabs that had formed Thursday/Thursday night on N-NE-E aspects appeared to have gained strength. Minimal signs of instability were observed as minor skier triggered cracking in isolated areas.

On Silver Peak, snowpit data was collected at the site of one of the most recent persistent slab avalanches known to have occurred in mid elevation terrain. This was compared to post avalanche snowpit data collected one week ago that had indicated ongoing instability on buried surface hoar. Yesterday's data found no trace of the previously problematic weak layer that existed at that location previously. On Mt. Tallac and on Trimmer Peak, snowpit data targeting the deep persistent slab problem had a few of the test results point towards some potential for ongoing instability. Several buried surface hoar layers were reported as identifiable in the snowpit on Mt. Tallac.

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