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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Non aggiornato — questo bollettino è scaduto 11 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Upper end MODERATE avalanche danger exists today for all elevations and aspects on slopes 35 degrees and steeper due to a combination of newly formed wind slab, storm slab, and loose dry avalanche problems. Natural avalanche activity in not expected today, but isolated natural activity is certainly not out of the question. Human triggered avalanches are expected today and should not be a surprise to backcountry travelers.

Problemi valanghivi

  • Wind Slabs

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

    A new round of wind slab development occurred last night and will continue to occur with ongoing SW to NW wind and snowfall today. These new wind slabs are depositing on top of lower density, minimally wind effected snow that existed at the snow surface yesterday. This will create easily identifiable strong over weak snow layering in areas where problematic wind slabs have formed. Shifting winds last night and today will expand the range of aspects, enhance wind slab layering, and create some wind slabs in less typical areas. Areas of cornice formation, wind pillows, and snow surface texture will provide clues for suspect slopes in near and above treeline terrain on NW-N-NE-E-SE-S aspects today. Wind slabs may be easier to trigger today than yesterday. If in doubt, stay on slopes less than 32 degrees in slope angle without steeper terrain above.

  • Loose Dry

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

    As multiple layers of recent storm snow stack up in wind protected areas below treeline, subtle differences between the snow in each layer may lead to storm slab development on all aspects. Human triggered snow surface cracking in wind protected areas is an indication that unstable storm slabs exist in the area. Staying on slopes less than 32 degrees in slope angle without steeper terrain above is an effective way to avoid this avalanche problem.

  • Wet Slabs

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

    In wind protected areas below treeline where no signs of storm slab instability exist, loose dry avalanches will be the more likely instability in steep terrain. If choosing to push the risk and venture onto slopes steeper than 35 degrees, evaluate the terrain for secondary hazards such as terrain traps, rocks, trees, and cliffs below that could greatly magnify the consequences of being pushed off line by a loose dry avalanche.

Avalanche Discussion

Observations made yesterday on Tamarack Peak and received from Mt. Baldy (both in the Mount Rose area) indicated that wind slab instability yesterday was small and isolated. One very small skier triggered wind slab avalanche was observed on the Far East Ridge of Tamarack Peak on N aspect in near treeline terrain. Some natural cornice collapse and a possible small wind slab avalanche crown line was observed on a wind loaded E aspect on the south ridge of Rose Knob Peak.

Snowpit work on Tamarack Peak near treeline on an E aspect at 9,675' indicated a potential weak layer with propagation characteristics along the bottom of the rain crust that exits at the old snow/new snow interface from the Jan 29-Jan 30 snowfall. In this area, the rain crust was found around 1.5 feet below the snow surface all the way up to the summit at 9,900'. By late this afternoon this rain crust may be closer to 2.5 feet below the snow surface in areas above 8,500'.

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