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 9 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

MODERATE avalanche danger exists above and below treeline due to a combination of wind slab and persistent slab avalanche problems. Significant uncertainly exists regarding the persistent slabs due to a change in weak layer of concern, isolated distribution, and a lack of data. Do not let an absence of signs of instability below treeline create a sense of security that discounts the possibility of an isolated avalanche problem.

Problemi valanghivi

  • Wind Slabs

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

    Wind slabs remain a concern, especially with a second round of snowfall and SW wind yesterday afternoon through last night. Near and above treeline areas on NW-N-NE-E-SE aspects is the most likely terrain for wind slabs to exist. With the lull in snowfall yesterday morning, new wind slabs may have built on top of existing wind slabs. Avalanche size to D2 is possible (large enough to bury or injure a person).

    Look for clues such as cornice formations, wind pillows, and stiff surface snow to help identify and avoid areas of potentially unstable wind slab.

  • Deep Persistent Slabs

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

    Don't get fatigued on messaging with persistent slabs. The nature of this avalanche problem has changed. The deeply buried facet layer that has been the focus of this avalanche problem for the past several weeks is not the main focus today. Different weak layers buried less than one foot below the old snow/storm snow interface are now the focus of the problem. Isolated areas of near crust facets, especially in the Carson Pass area and buried surface hoar that had been observed in several locations around the forecast area pre storm are now the weak layers of concern. Data is lacking creating increased uncertainly.

    The location of this problem is near treeline and below treeline terrain on NW-N-NE aspects. Many of the below treeline open areas for this problem do not look like avalanche paths so remain focused on slope angle. The weak layer distribution is isolated so it will be easy to go all day seeing no signs of instability below treeline. Avalanche size D2 is expected with the isolated possibility to size D3.

    Keep a vigilant watch for snow surface cracking and/or snowpack collapse with a possible whumpfing sound in wind protected areas. These are signs of an unstable snowpack related to this avalanche problem.

Avalanche Discussion

* Natural wind slab avalanches were reported yesterday 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.

* Additional signs of instability were difficult to find yesterday while traveling on Tamarack Peak and on Andesite Ridge.

* No areas of buried surface hoar were examined yesterday so avalanche activity is unknown. Significant uncertainty remains regarding stability in any areas were buried surface hoar exists.

Regioni coperte