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

In sintesi

MODERATE avalanche danger still exists on wind loaded near and above treeline NW-N-NE-E-SE aspects steeper than 35 degrees due to lingering wind slabs. Depending on the amount of daytime warming that occurs today, enough wet snow may form on the E-SE-S-SW-W aspects steeper than 35 degrees for the avalanche danger to rise to MODERATE on those slopes as well due to loose wet snow instabilities. Human triggered avalanches remain possible today.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    3

    Two wind slab avalanches (one skier triggered and one triggered by an intentional cornice drop) that occurred yesterday as well as evidence of several other avalanches that occurred early Thursday morning during the storm were reported to the avalanche center yesterday. Wind loading and wind transport continued all day yesterday and last night and means that human triggered wind slab avalanches will remain possible today even though they may have grown more difficult to trigger. Due to the duration and strength of the winds a mix of firm, hard wind slabs that could break above the person that triggers them and softer wind slabs will exist on wind loaded slopes. Wind loaded N-NE-E aspects and cross loaded NW and SE aspects steeper than 35 degrees in near and above terrain represent the most likely places to find unstable wind slabs. Wind loaded couliors, unsupported slopes, convex rollovers, and slopes in complex or extreme terrain remain especially suspect. These wind slabs will most likely fail on weaknesses within the storm snow like density changes or graupel layers. The wind slab avalanches that remain possible today could still involve enough snow to have serious consequences.

    Clues like recent wind slab avalanches on similar slopes, shooting cracks on lower angle wind loaded terrain, cornices above a slope, blowing snow, wind drifted snow, ripples in the snow surface, firm hollow sounding snow, and other wind created textures can help identify where wind slabs may exist. Use observations and clues like these to find where the wind slabs lurk and then avoid those wind slabs and their run out zones.

  • Loose Wet

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

    Today's warmer temperatures combined with periods of sun may provide enough warming for some loose wet snow instabilities to become possible as the recent snow starts to warm up. The forecasted cloud cover and light winds should limit the loose wet instabilities that do form and should prevent larger more widespread loose wet avalanches. Isolated, small loose wet point releases, roller balls, and pinwheels should comprise the majority of the loose wet instabilities that form today unless the forecasted cloud cover does not materialize and/or the temperatures climb higher than forecasted. More sun and higher daytime temperatures would mean larger and more widespread wet snow instabilities. 

Avalanche Discussion

Yesterday wind slab avalanches occurred on Andesite Ridge (Donner Summit) and on a lower east facing slope on Slide Mountain (Mt. Rose area). On Andesite Ridge the crown depth measured 12 to 18 inches in depth and on Slide Mountain it measured 12 inches. A skier triggered the avalanche on Slide Mountain and an oven sized piece of cornice dropped onto the slope from above triggered the slide on Andesite Ridge. Wind transport and loading continued to occur at both of these locations yesterday. 

Other observations from Rose Knob Peak, Castle Peak, Luther Pass, and Stateline Ridge also showed continued wind loading in exposed areas. Snowpit tests on wind slabs on Castle Peak yielded unstable results that failed within the wind loaded snow. Tests on Rose Knob Peak and Stateline Ridge did not produce unstable results and indicated that the wind slabs have gained some strength. In more sheltered non wind affected areas near and below treeline, observations in all of these areas showed a more consolidated snowpack and signs of instability proved difficult to find.

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