Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Thu
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
4 · Forte
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In sintesi

A large avalanche occurred yesterday in the Frog Lake/Castle Peak area involving a group of backcountry travellers.  Increased uncertainty exists with ongoing reactivity of these buried weak layers under this large storm snow load.  The potential continues for large to very large avalanches occurring in the backcountry today.  HIGH avalanche danger continues with travel in, near, or below avalanche terrain not recommended. 

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1.5–3

    Multiple feet of snow has fallen over the past few days along with gale force winds.  While this storm is winding down this morning, continued loading of the snowpack with additional light snowfall and wind transport will occur today.  Large to very large avalanches remain a very real concern with ongoing uncertainty with how weak layers will respond to this large storm snow load.  Travel in or below avalanche terrain is not recommended for today.

    Storm snow instabilities could take the form of slabs or sluffs today in many locations.  Slabs of wind drifted snow will continue to form in wind exposed areas below ridges, in gully features, and on open slopes as wind speeds remain strong to gale force through tonight.  Weaknesses within the storm snow along with at the old snow/new snow interface have been observed during the storm.  Colder temperatures could potentially slow settlement rates and stabilization of the snowpack.  

    The Feb. 10 facet layer exists on NW-N-NE aspects in mostly wind protected terrain above around 7500 feet.  The avalanche accident that occurred yesterday may have involved this weak layer.  Avalanches involving this weak layer would be large to very large in size, could break wider than expected, and could be triggered mid-slope or below.

      

Avalanche Discussion

An avalanche was reported yesterday in the Frog Lake/Castle Peak area of Donner Summit involving a large group of backcountry travellers.  SAR operations began yesterday afternoon and are still underway with people still missing.  We have an avalanche observation here.  Perry Peak near Frog Lake/Castle Peak  We will update this page as more information becomes available.   

Weak sugary snow (near-surface facets) formed on many NW-N-NE aspects during the recent, extended dry spell in January. This weak layer was buried by new snow on Feb 10. Most areas have a thin rain crust along the top of this facet layer up to 8,600 to 8,800 ft.  This weak layer is still a concern for today with uncertainty surrounding the ease of triggering large avalanches.  Weak layers, similar to the Feb 10 facet layer, have contributed to large avalanches and avalanche fatalities within our forecast area in the past.

Lower elevation areas and sun-exposed slopes experienced significant snowmelt over the past 3 weeks, exposing areas of dirt, rock, and downed trees.  These hazards and obstacles now lie hidden, covered by low density new snow. This creates a hazard situation similar to early season coverage in some areas.  Additionally, deep open holes, open creeks, and ponded water are widespread in low-lying areas, especially below 8,000'. 

Regioni coperte