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

In sintesi

MODERATE danger already exists on slopes steeper than 35 degrees on all aspects and elevations due to the presence of unfrozen loose wet snow. MODERATE danger will persist throughout the day as more loose wet snow forms resulting from daytime warming and rain impacting the area. Loose wet avalanches large enough to threaten backcountry travelers will be possible again today. Evaluate snow and terrain carefully. Identify and avoid the areas where wet snow deep enough for loose wet avalanches exists. 

Problemi valanghivi

  • Loose Wet

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

    Some cloud cover last night and overnight lows well above freezing should have prevented much of a refreeze from occurring. If any of yesterday's wet snow did refreeze, it will not stay frozen long. Today's warm temperatures, some morning sunshine, and some afternoon rain will allow wet snow to form on all aspects. Once the snowpack becomes wet, it becomes weak since the ice bonds that give the snowpack strength will have melted away leaving deep, loose, wet snow sitting on the slopes. Loose wet avalanches will be possible on slopes steeper than 35 degrees wherever loose wet snow exists. Loose wet activity will become possible on the E-SE-S-SW-W aspects at all elevations first and then progress to the NW-N-NE aspects as they warm up a little later. Once it starts raining, loose wet avalanches will be possible on any slopes where the rain falls. Most of the wet snow instabilities should manifest as loose wet avalanches but other forms of wet snow instabilities like glide cracks or wet slabs are not impossible. 

    Due to a lack of overnight refreeze, expect the snowpack to become unsupportable earlier today than on previous days. In some areas it may already be unsupportable since it never refroze. As soon as an unsupportable snowpack exists, it is time to move to more frozen aspects if they are available, onto lower angle slopes away from anything steep, or to head for an activity that does not involve snow.

    Stepping off your equipment and sinking into wet snow above your boot tops and small surface instabilities like roller balls, pinwheels, or point releases can provide clues that enough wet snow has formed for larger loose wet avalanches to become an issue. Terrain traps like gullies, creeks, and cliffs can greatly increase the risk of any size loose wet avalanches.

Avalanche Discussion

Yesterday observations on Castle Peak found that after a very short window of supportable corn conditions before 10:30 am, the snowpack started becoming unsupportable on the sun-exposed E-SE-S aspects as early as 10:30 am. Ski kicks on test slopes triggered loose wet avalanches that entrained 6 to 8 inches of wet snow on E aspects at 8100 ft. by 11:00 am. Shortly after this time, SW-W aspects that had held supportable melt freeze conditions also started to become unsupportable. By noon boot top deep wet snow also existed on these aspects, and ski cuts triggered similar loose wet avalanches. These deep wet snow conditions existed up to at least 8600 ft. by midday. Northerly aspects held supportable melt freeze conditions with 1-3 inches of wet snow resting on top of frozen crusts and transitional snow at noon. One large cornice collapse had occurred on a wind loaded NE aspect within the last 2 days, and craks had formed on the ridgelines behind the remaining cornices. 

Regioni coperte