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
3 · Marqué
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Périmé — ce bulletin a expiré 8 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

CONSIDERABLE avalanche danger exists today at all elevations. Wind slab, persistent slab, and possibly storm slab avalanche problems are expected in the backcountry. Large high consequence avalanches could occur today.

Problèmes avalancheux

  • Wind Slabs

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

    New snow and wind will combine to create new wind slabs today. The vast majority of wind slabs will form near treeline and above treeline on NW-N-NE-E-SE aspects. Avalanche size up to D2 is possible (large enough to bury a person).

    Identify and move cautiously around areas where drifting snow is depositing, especially on or below slopes with cornice features or wind pillows. This is the most likely avalanche problem today but the persistent slab problem is more worrisome.

  • Deep Persistent Slabs

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

    The possibility of a large and destructive persistent slab avalanche is worrisome today (size D3). New snow loading on top of a weak layer with a high degree of uncertainty makes for challenging route finding both uphill and down. The often deeper than expected and wider than expected failure of persistent slab avalanches adds additional exposure from terrain either above or to the side. Becoming caught in a persistent slab avalanche today may not be survivable. Be conservative with terrain selection. If snowpack collapse, whumpfing, or other signs of deep instability are encountered, avoid avalanche terrain including low angle areas with steeper slopes above.

    The problematic weak layer is faceted snow found below the 2 to 4 feet of recent storm snow deposited 1/5-1/7. This layer is most prominent along the Sierra Crest on northerly aspects between 7,000' and 8,000' in below treeline and near treeline terrain. Isolated areas of ongoing instability have been observed with easier triggering where this weak layer is buried just a couple feet deep. The additional new snowfall today is adding additional stress to this weak layer.

  • Loose Dry

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

    A storm slab avalanche problem may form today above 7,000' in any areas that receive close to a foot of new snow. If this problem forms it will be found in wind protected areas near treeline or below treeline on any aspect. Avalanche size up to D2 (large enough to bury a person) may occur in isolated areas.

    Look for snow surface cracking of just the new snow in wind protected areas as a sign of instability associated with this avalanche problem.

Avalanche Discussion

* Faceted snow found 2 to 4 feet below the recent storm snow continues to be problematic in isolated areas. Yesterday a party triggered a large snowpack collapse with a whumpf sound on Elephant's Hump near Red Lake (Carson Pass area) on a NE aspect at 7,800'. An avalanche course traveling in Shirley Canyon (Outside Squaw Valley) also reported triggering several collapses with a whumpf sound. Other parties looking at this same weak layer in various other Sierra Crest locations found limited evidence of ongoing instability indicating increased uncertainty. Please continue to report your findings associated with this weak layer.

* Rapid settlement of recent storm snow has made the upside-down upper snowpack from the tail end of the 1/5-1/7 storm cycle more supportable.

Régions couvertes