Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

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

Snowpack stability is improving, but a low likelihood high consequence persistent slab avalanche problem lingers below treeline and near treeline. Warming conditions and light rain on snow this afternoon and tonight below 8,000' may trigger some rollerballs and very small loose wet snow avalanches. MODERATE avalanche danger continues below treeline and near treeline with LOW avalanche danger above treeline.

Problemi valanghivi

  • Deep Persistent Slabs

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

    Below treeline and near treeline NW-N-NE-E aspects remain the areas of concern. The Jan 4 crust/facet persistent weak layer in these areas is slowly gaining strength but has not fully stabilized. In most below treeline locations, this weak layer is buried 1 to 2 feet below the snow surface. In some near treeline areas, this weak layer is buried up to 8 feet below the surface under wind drifted snow. Human triggered avalanches size D2 to D3 have moved down to unlikely on a regional scale, but isolated instability is still a consideration.

    A low likelihood high consequence avalanche problem is what we are working with at this time. The persistent Jan 4 crust/facet weak layer is gaining strength, but not at the same rate in all locations. We are not quite past this avalanche problem on a regional scale. Make conservative terrain and route selections in any areas where unstable snowpit test results or other signs of instability exist.

  • Loose Wet

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

    Light rain on snow this afternoon and tonight below 8,000' may trigger some rollerballs or very small loose wet avalanches. Avalanche size is expected at D1. Problematic consequences of being caught would come from downslope terrain hazards such as cliffs and terrain traps below.

Avalanche Discussion

* Wind slabs observed yesterday on Mt. Judah in lee areas near and above treeline were 4 to 12 inches thick and difficult to trigger. Cornices collapsed with moderate difficulty and did not cause wind slab failure on test slopes.

* The last reported persistent slab avalanche occurred 4 days ago.

* Snowpit tests targeting the persistent Jan 4 crust/facet layer have shown increasingly variable results over the past several days and fewer unstable results.

Regioni coperte