Lawinenlagebericht

Central Sierra Nevada

Sierra Avalanche Center
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Lawinengefahr

Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Avalanche danger is MODERATE near treeline and above treeline where another round of wind slab formation is expected to have occurred last night. Below treeline avalanche danger is LOW where triggering an avalanche on a regional scale is unlikely but not impossible. Persistent slab and loose wet avalanche problems have a high degree of uncertainty today.  

Lawinenprobleme

  • Wind Slabs

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

    Last night brought a third round of potential new wind slab formation as SW winds increased late yesterday through last night. Ridgetop areas observed yesterday held a foot or more of recent storm snow that was available for wind transport. Last nights winds are expected to have redistributed this snow on the ground creating new wind slabs in near treeline and above treeline areas on NW-N-NE-E-SE aspects. Avalanche size up to D2 is possible (large enough to bury or injure a person).

    Human triggered and naturally occurring wind slab avalanches were reported on Thursday and Friday. Look for signs of recently wind drifted snow in the form of cornices, wind pillows, and wind sculpted snow surfaces. Use these clues to identify and avoid areas of potentially unstable wind slab.

  • Deep Persistent Slabs

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

    Hang in there and continue to pay attention to the changing details of this avalanche problem despite prolonged messaging. Continued concern is focused on a near crust facet layer that was observed 8 to 12 inches below the old snow/storm snow interface in the Carson Pass area. This weak layer was observed pre storm at Crater Lake, Meiss Meadows, Elephants Hump, and Squaw Ridge. Limited data as to the stability of this old snow weak layer following new snow loading is leading to increased uncertainty. Near treeline and below treeline areas on NW-N-NE aspects is were this avalanche problem may exist. Avalanche size to D2 is anticipated with isolated possibility to size D3.

    Look for and avoid avalanche terrain in any areas where snow surface cracking, snowpack collapse with a possible whumpfing sound, and/or unstable snowpit test results are occurring.

    Concern for this avalanche problem continues to decrease on a regional scale as the deeply buried facet layer from December and the now unreactive buried surface hoar are no longer the main focus of this avalanche problem. Concern remains elevated for the Carson Pass area and for any yet to be observed areas where this same near crust facet layer exists.

     

  • Loose Wet

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

    As air temperatures at the mid and upper elevations climb above freezing today, loose wet avalanche activity will become possible on SW-S-SE aspects. Natural roller balls may occur as snow falls off of rocks and trees onto steeper slopes. Small (size D1) human triggered loose wet avalanches will become possible as daytime warming progresses. If warming today is not quite sufficient to get this avalanche problem going, additional warming on Sunday will likely get it started.

Avalanche Discussion

* A skier or snowboarder triggered wind slab avalanche occurred Friday in the Bronco Chutes of Relay Peak (Mount Rose area) This avalanche occurred in response to a ski cut in complex above treeline terrain on a NW aspect with an approximate slope angle of 45 degrees. The crown was reported as 12 to 16 inches deep. Avalanche size was reported at D2 (large enough to bury or injure a person).

* A second potential wind slab avalanche was noted Friday in the Bronco Chutes area but lighting and distance made discerning details difficult.

* Natural wind slab avalanches were reported Thursday from The Far East Ridge of Tamarack Peak (Mount Rose area) and from the south end of Andesite Ridge (Donner Summit area). In both cases, cornice fall may have been the trigger. Debris were covered with new snow indicating that the avalanches had occurred either Wednesday night or very early Thursday morning.

* Snowpit data targeting buried surface hoar was collected Friday from sites where it was confirmed to exist pre storm on Silver Peak (Pole Creek area) and on Castle Pass (Donner Summit area). In both areas the surface hoar was bonded into the snowpack and no longer produced failures in snowpit tests.

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