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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Kernpunkte

CONSIDERABLE avalanche danger exists at all elevations due to a combination of wind slab, storm slab, and loose wet avalanche problems. Human triggered avalanches should not be a surprise to backcountry travelers today.

Lawinenprobleme

  • Wind Slabs

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

    The wind slab avalanche problem continues today. In some cases wind slab avalanches occurred naturally, in other cases they have been difficult to trigger (stubborn). When avalanches have occurred over the past few days, size has mostly been D2 to D3. The vast majority of wind slabs exist near treeline and above treeline on NW-N-NE-E-SE aspects. Unstable wind slabs may be encountered to a more isolated extent on other aspects and below treeline due to the strength of the wind. Some of these wind slabs may take on some wet slab characteristics today in sun exposed areas.

    Identify the problem areas to avoid. Use clues such as blowing snow, cornices, wind pillows, and snow surface texture to locate where unstable wind slabs are likely to exist. Move around these areas with a wide margin for error. Do not underestimate the avalanche size potential, potential width of propagation, or potential run out distance. Do not fall into the trap of making stability assessments based on previous tracks. Remember, triggering has been stubborn in some cases.

  • Loose Dry

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

    Additional snowfall last night with the highest snow levels of this event have kept the storm slab avalanche problem ongoing. The most recent new snow is upside-down providing slab over less dense snow below. Wind slabs may be encountered in wind protected below treeline to near treeline terrain on any aspect. Expected avalanche size is D1 to D2. Some of these storm slabs may take on some wet slab characteristics today in sun exposed areas.

    Search for evidence of instability in the form of recent avalanches, snow surface cracking while breaking trail, or unstable snowpit test results. If instability exists, make conservative terrain and route choices both uphill and down.

  • Loose Wet

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

    It's nearly March and the associated higher sun angle and stronger solar radiation have crept in during the recent weeks of storms. As sun breaks occur today, expect roller ball and loose wet avalanche activity to occur just about anywhere. Avalanche size is not expected to exceed D1, so the consequences will come from terrain hazards such as being carried over cliffs or into terrain traps, rocks, trees, etc.

Avalanche Discussion

* Additional reports of natural slab avalanches with crowns of 2 to 3 feet have been received. These avalanches occurred on a variety of aspects both above and below treeline. Avalanche size has been mostly D2 with at least one D3 reported that closed the railroad. In some cases, crowns have been 1/4 mile wide. Early indications are that two distinct natural avalanche cycles have occurred, one on the morning of Feb 26 and a second on the morning of Feb 27.

* Evidence of instability has been quite variable both spatially and temporally during this storm cycle with some parties encountering little evidence of instability despite the natural avalanche activity elsewhere.

* Tree bombing, rollerballs, and a few small (size D1) loose wet avalanches were noted yesterday, mainly at the lower elevations.

* Cornices are large, fragile, and breaking off easily.

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