Lawinenlagebericht

Central Sierra Nevada

Sierra Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
4 · Gross
Waldgrenze
4 · Gross
Unterhalb
4 · Gross
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Kernpunkte

High intensity snowfall and gale force winds will continue today. Slabs of new snow are expected to avalanche on steep slopes today and tonight, possibly failing deep in the snowpack. Travel in, near, or below avalanche terrain is not recommended at this time.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Very Likely
    Größe
    2–3

    Unstable wind slabs will continue to grow in size and distrubution today where gale-force SW winds continue to drift and deposit wind-blown snow onto slopes near ridgelines and into gullies. Existing wind slabs are becoming thick and the resulting avalanches could be deep. The majority of wind slabs exist on NW-N-NE-E-SE aspects in near treeline and above treeline terrain. Wind slabs may also form to a lesser extent below treeline due to the strength of the wind.

    Natural and human triggered wind slab avalanches are expected today. These avalanches could be very large and run down into below-treeline areas. Travel in, near, or below avalanche terrain is not recommended at this time. Expect poor visibility today with limited ability to see terrain above you.

    (2/27/2023)

    Small wind slabs were reactive yesterday morning before the storm really even got started. Powderhouse Peak, Luther Pass, CA

    Photo: SAC

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Very Likely
    Größe
    2–3

    Snowfall rates around 2 inches per hour today will allow new snow to accumulate faster than it can bond to itself. While shallow dry loose instability may present on the snow surface, deeper storm slab instability is now a concern. Various weak layers exist several feet below the snow surface on NW-N-NE aspects. The most notable is at a lightly faceted crust at the Feb 21 old/new snow interface. This is right at the bottom of all of the recent new snow accumulated since last Tuesday. Isolated snowpack collapses, whumpfing, test slope failure, and unstable snowpit test results have been observed at the bottom of the recent storm snow. The rapidly deposited new snow load today and tonight may overwhelm these deeper weak layers, contributing to avalanches that fail deep and wide.

    Travel in, near, or below avalanche terrain is not recommended at this time. Becoming caught in an avalanche below treeline that fails deep in the snowpack may not be survivable.

    (2/27/2023)

    Unstable snowpit test result (ECTP) down on faceted crust at the Feb 21 old/new snow interface. Stepping off skis at this location to dig the pit triggered a collapse and whumpf.  Schallenberger Ridge, Donner Summit, CA

    Photo: SAC

Avalanche Discussion

Recent Observations:

  • The amount of avalanche activity that occurred during the past 24 hours is unknown due to storm conditions and poor visibility.
  • Intense blowing snow has occurred in near and above treeline areas over the past two days. Some blowing snow has been reported in open areas below treeline as well. 
  • Concerning weak layers exist around 4 feet deep in the snowpack in wind protected areas on some NW-N-NE aspects. These weak layers will become buried another 1 to 2 feet deeper today in wind protected terrain and even deeper in areas where wind drifted snow deposits.

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