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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In sintesi

Moderate avalanche danger continues at all elevations due to a persistent slab avalanche problem as our existing snowpack continues to weaken over time.  Human triggered avalanches are possible throughout the forecast region in isolated areas.  Identify and avoid areas of concern.  This avalanche advisory will be updated by 7am on Tuesday, January 2.

Problemi valanghivi

  • Deep Persistent Slabs

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

    Persistent slab avalanches are possible on NW-N-NE aspects at all elevations.  The current dry spell through much of December has allowed our existing snowpack to facet and lose strength over time creating a layer of loose sugary snow.  This layer of weak faceted snow has recently become reactive to the weight of a person, causing cracking, whumpfing, and unstable snowpack tests results.  While faceted snow is widespread on many NW-N-NE aspects, having a slab on top is not.  In isolated areas near and above treeline, hard wind slabs are on top of this faceted weak layer.  In isolated areas below treeline, soft slabs are on top of this faceted weak layer.  This will be an ongoing problem as this weak layer continues to facet and lose strength. 

    Look for cracking around skis, whumpfing sounds, and any signs that a slab may exist above weak faceted snow.  Hand pits may help to see if there is a cohesive surface slab on top of loose faceted snow.  Use safe travel protocols when traveling in and around avalanche terrain.  The consequences of being caught in an avalanche are elevated, even a small one, with our low snowpack conditions.

Avalanche Discussion

* Signs of persistent slab instability on NW-N-NE aspects including snow surface cracking, whumpfing, and/or unstable snowpit test results have occurred during the past several days in the Carson Pass, Desolation Wilderness, West Shore Tahoe,  Deep Creek, Pole Creek, and Donner Summit areas. In all cases, failure occurred on faceted snow beneath either a hard or soft slab.

* Near surface facets without an overlying slab are fairly widespread on northerly aspects in wind protected, below treeline areas.

* Snow surface conditions range from wind scoured snow and firm ice near and above treeline to lingering areas of soft unconsolidated snow on sheltered northerly aspects below treeline.

* Northerly aspects above 8000 ft in the Mt. Rose area and along the Sierra Crest north of Emerald Bay hold the best snow coverage at 2 to 3+ feet. Overall less snow cover exists south of Emerald Bay, but decent coverage exists above 8,500 ft. on northerly aspects in the Carson Pass area.  Coverage becomes patchy on other aspects with large areas of bare ground on many southerly aspects at all elevations.

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