Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 11 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Avalanche danger is LOW for all elevations and aspects. Please keep in mind that LOW danger does not mean no danger. Human triggered avalanches are unlikely but certainly not impossible today. Areas of wind slab and loose wet instability are expected in the backcountry today. Normal caution is advised.

Problemi valanghivi

  • Wind Slabs

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

    Shifting ridgetop winds over the past few days have produced wind slabs 1 to 3 feet deep in lee areas. The strongest period of NE winds post storm event occurred Saturday night and was the contributor to the majority of development of the recently formed wind slabs. Increasing NE ridgetop winds today will transport the 1 to 5 inches of new snow that was deposited during snow showers yesterday. Forecast wind speed for today is expected to transport only the few inches of new snow from yesterday keeping any additional wind slab development small. One caveat: If actual wind speeds today exceed forecast amounts, there is plenty of snow available for wind transport near and above treeline which could lead to larger than expected and more unstable than expected wind slab development. Glossary of terms

  • Loose Wet

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

    With clearing skies in the forecast for today, the stronger levels of March solar radiation will affect the snowpack. Significant amounts of snow is expected to begin falling off of rocks and trees, leading to roller ball activity. Human triggered pin wheels are expected in sun expose areas as minute amounts of free water form at the snow surface. The vast majority of loose wet instability is expected to occur below 8,000' as roller balls and pin wheels, with more limited amounts at higher elevations. Actual loose wet avalanches are an unlikely but not impossible event today in sun exposed areas at any elevation on slopes 37 degrees and steeper.

Avalanche Discussion

Observations made yesterday on Incline Lake Peak (Mount Rose area) indicated that settlement and bonding has occurred within the snowpack. Settlement cracks up to 2 inches wide were noted at the upper elevations. Recent new snow appeared well bonded to both itself and to either crust or old near surface facets that exist at the old snow/storm snow interface. Wind scouring and subsequent wind slab formation were noted along the summit ridge from recent NE winds. Wind slabs up to 1 foot thick were observed in lee areas. These slabs appeared well bonded with only minimal skier triggered cracking observed while traversing these slabs in low angle areas. These observations matched well with other recent observations from around the forecast area. Glossary of terms

What about Persistent Slabs?

Snowpit data collected over the past few days has yet to reveal areas where persistent slab instability has formed. The necessary set of slab and weak layer characteristics have not been observed all in the same place at the same time. Areas where the buried near surface facet weak layer is most well developed are also the areas that received the least amount of storm snow and have a minimal new snow load. In areas of greater amounts of storm snow and significant new snow load, the new overlying slab has been slow to become highly cohesive. This has allowed time for the old near surface facets to increase the degree of rounding and subsequent strength under the insolation of the storm snow layer. Field observations will continue to monitor this layer interface where it exists above 8,000' on NW-N-NE aspects in near treeline and below treeline terrain. For now, persistent slabs are removed from the list of avalanche problems until such a time that field observations indicate problematic development. Glossary of terms

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