Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 8 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

3pm UPDATE - Due to higher than forecasted snowfall amounts the avalanche danger has increased to CONSIDERABLE. The avalanche danger will remain CONSIDERABLE through the night. Check back at 7 am tomorrow for the next update.

 MODERATE avalanche danger will continue. Large persistent slabs remain a concern. Wind slabs and storms slabs could become possible this afternoon and during the night as new snow and wind impact the region.

Problèmes avalancheux

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2

    No persistent slab avalanches have been reported since the one on Castle Peak on Jan 11. Significant uncertainty about how widespread this problem may be or how large a trigger it would take to release such a slab still exists. Some data still indicates that fractures could still propagate along the buried persistent weak layer (facets) and some data indicates that this layer may be dormant in many areas. The additional snow load expected this week could reactivate this weak layer in some areas.   

    While the likelihood of triggering a persistent slab avalanche may be low, the consequences of a large destructive avalanche are high. Pay close attention to areas where large triggers like cornices looming above a slope may exist and make a plan with your group to manage terrain with appropriate safety margins.  

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1

    New wind slabs will start to form as new snow and wind impact the forecast area. These should remain small during the day due to limited snow accumulation and less strong winds. As snow accumulation and winds increase this afternoon/evening, wind slabs will quickly grow in size and become more widespread during the night. Natural wind slab avalanches will become possible tonight.

  • Loose Dry

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1

    Light snowfall with light winds since yesterday may have buried and preserved the widespread surface hoar layer. This layer of weak feathery snow could serve as a weak layer as more snow accumulates on top of it. Storm slab avalanches that fail on this layer or on other new snow weaknesses could become possible later this afternoon/evening and could grow in size and distribution during the night. Natural storm slab avalanches will become possible tonight.

Avalanche Discussion

* Snowpit tests and observations targetting the old weak snow layers (facets) on Castle Peak, Hidden Peak, and in Johnson Canyon yielded variable results consistent with other data collected in various locations since Jan 11. Some tests and data showed a dormant weak layer with no signs of instability and some indicated that if this layer breaks fractures could still propagate through the facets. All data indicates that it would take a very large trigger to initiate such a break. 

* Fragile feathery surface snow (surface hoar) existed on top of the snowpack in open areas in Johnson Canyon, Ward Canyon, Chief Creek, and Hidden Peak yesterday. Observers also found it to be widespread in areas along Donner Summit, Echo Summit, and in the Carson Range east of Lake Tahoe on Sunday.

Régions couvertes