Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Thu
Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

A storm will begin late this afternoon through Thursday bringing increased winds and snow to our area.  This new snow will add additional weight to our variable and, in some cases, weak snowpack.  Over the snow recreation continues to be limited for backcountry travelers due to low snow conditions.   Avalanche danger is expected to quickly rise this evening and overnight.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–1.5

    SW winds will be in the strong to gale force range today.  Snow available for wind transport remains limited, but small amounts of blowing snow will occur forming small winds slabs in near and above treeline terrain.  As snow begins to fall late this afternoon and tonight, larger wind slabs will begin to form in these areas.  In some terrain where wind slabs will be forming, previous weak faceted snow exists that could easily be overloaded by the newly forming wind slabs.

    Look for blowing snow, new cornice development, and wind pillows as to where wind slabs will be forming.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–1.5

    Weak faceted snow continues to exist on NW-N-NE aspects above 8500' with weak facet/rain crust combinations existing below 8500’.  These weak layers are highly variable in distribution and strength with a high level of uncertainty.  The forecasted storm starting late this afternoon through Thursday, will add considerable weight to our weak snowpack structure.  This additional weight could overload these weak layers causing avalanches to occur.    

    Any snowpack collapses, whumpfing sounds, or shooting cracks represent signs of unstable snow. If you encounter any of these signs of instability, avoid NW-N-NE aspect avalanche terrain in the area.

    (12/4/2023)

    Shallow  and weak snowpack on N side of Hourglass Bowl.   Tamarack Peak.

    Photo: SAC

Avalanche Discussion

1 to 2 feet of snow can be found on NW-N-NE aspects above 8000' throughout the forecast region. Continuous snow cover starts around 7,200' to 8,000' along the Sierra Crest and 8000’ to 8500’ in the Carson Range. There is a high level of variability in the structure of the existing snowpack depending on elevation and location with concerning weak layers in some areas on NW-N-NE aspects. Generally, below 8000-8500' are a mix of rain crusts and faceted snow combinations.  Areas above 8500' to 9000' are mostly all faceted snow and depth hoar with thinner or no rain crusts present. 

Previous NE wind events scoured the upper portion of many wind exposed slopes down to rock, dirt, and/or ice before the recent snowfall. Despite this scouring, weaker faceted snow persisted on the lower portions of many slopes. A much thinner snowpack or bare ground exists across E-SE-S-SW-W aspects.

While the snowpack has become more usable for over the snow travel, there is still the potential to hit many obstacles (rocks, logs, open water, bushes, etc.) that are barely covered. Areas with a supportable rain crust are the most usable in the 7500’ to 8500’ elevation range. If you are traveling on snow for recreation, you should come up with a daily travel plan based on the current conditions and associated hazards. Anticipate encountering a different snowpack structure and a different set of travel conditions if you are moving from one place to another around the forecast area.

Regioni coperte