Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

MODERATE avalanche danger exists near and above treeline on all aspects on slopes steeper than 35 degrees due to wind slabs formed by recent SW and NE winds. Persistent slabs are on ongoing problem on N aspects with MODERATE danger both above and below treeline on slopes steeper than 30 degrees in specific areas. LOW danger exists in most areas below treeline, with the exception of N aspects.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1

    Strong to gale force NE winds last night will have further redistributed snow on the ground, creating a new round of wind slabs in near and above treeline areas. SE-S-SW-W-NW aspects are the most likely location for problematic wind slabs to exist today, but unstable wind slabs may exist in isolated areas on N-NE-E aspects as well.

    With significant wind transport of snow by SW winds 24 hours ago followed by wind transport of snow by NE winds last night, determining where the most recent wind slab formation has occurred could be tricky in some areas. Looking for wind pillows and reading sastrugi formation will be more helpful than simply looking for cornices.  

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2

    Persistent slabs remain an ongoing avalanche problem. The weak layer is faceted old snow buried 2 to 3 ft below the surface on N aspects above 8300' in the northern portion of the Sierra Crest, above 9300' in the Mt. Rose area, and in isolated areas above 9,000' in the southern portion of the forecast area. Snowpit data continues to point to some degree of problematic instability on a daily basis. That said, most snowpit data is not indicating that snowpack failure is imminent, but an avalanche could occur from the right trigger placed in the right spot on the right slope.

    One of the greatest challenges is that the location of this avalanche problem matches the locations that have the best coverage and are therefore most inviting for skiing/riding. Consider what information is truly known vs unknown before committing to travel in avalanche terrain on N aspects. Most informal observations do not give reliable information and existing tracks do not indicate stability when dealing with persistent slabs. Digging in the snow is likely required to see if this problem exists on the specific slope in question. Avoiding N aspects steeper than 30 degrees is the simplest strategy for dealing with this persistent weak layer, especially if one has an aversion to or insufficient knowledge of snowpit work. Keep in mind that snowpit work never proves stability, it only shows potential signs of instability.

Avalanche Discussion

Observations made and received yesterday from Silver Peak (Pole Creek area), the south ridge of Deep Creek, Tamarack Peak (Mount Rose area), and Waterhouse Peak (Luther Pass area) showed some signs of instability. A small natural wind slab avalanche was noted on a N aspect in Deep Creek following the strong SW winds yesterday morning. Snowpit data on Silver Peak and Waterhouse Peak plus an isolated whumpf on Waterhouse Peak gave indications of problematic layering below the recent storm snow at the old/new interface and/or on more well developed faceted snow in the lower half of the snowpack. In the Mount Rose area, evidence of significant wind transport of snow on the ground was noted.

The deepest and most usable snowpack within the forecast area exists along the northern portion of the Sierra Crest. Along the Sierra Crest south of Tahoe City, snowpack depths decrease, even at the highest elevations. Recent storms have added to the snowpack in all areas but many rocks and shallowly buried obstacles still exist. The Mount Rose area in the NE portion of the forecast area has decent snowcover, but impact with rocks remains likely at the lower elevations in this area as well.

All of the recent avalanche and snowpack observations submitted by local users have been greatly appreciated and have contributed towards producing the best possible avalanche advisories. Please continue to submit observations through the "submit observations" buttons found throughout this website.

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