Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Alpin
2 · Modéré
Limite forestière
2 · Modéré
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

MODERATE avalanche danger continues today for all elevations. Loose wet avalanches may occur. An unexpected deep slab avalanche was remotely skier triggered yesterday leading to a high degree of uncertainty. Strive to create larger than normal margins of safety while traveling in or below avalanche terrain today.

Problèmes avalancheux

  • Loose Wet

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

    Another round of rapid warming is expected today. Surface wet snow formation will occur with the continued possibility of loose wet avalanches. Loose wet instability is most likely on E-SE-S-SW-W aspects today. Loose wet avalanches may occur on NW-N-NE aspects as well, especially at the mid and lower elevations. Avalanche size is expected to range from very small up to large enough to bury or injure a person (up to size D2).

    Natural and human triggered roller balls are an early sign of developing wet snow instability. Avoid travel on steep slopes in areas where roller balls are occurring.

  • Storm Slabs

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

    Inclusion of this problem today is based entirely on the unexpected remotely triggered deep slab avalanche that occurred yesterday on Mt. Houghton (Mount Rose area). There are a significant number of unknowns about this avalanche, leading to a high degree of uncertainly in regards to the problematic weak layer, aspect distribution, and elevation distribution of this problem. Avalanche size up to D3 is possible (large enough to bury and destroy a car, damage a truck, destroy a wood frame house, or break a few trees).

    This is a very difficult avalanche problem to manage in the field. Triggering is often much less predictable than the locally more common wind slab and storm slab avalanches. Human triggering may occur above, below, or off to the side of the slope. Deep slab avalanches frequently occur on slopes covered in previous tracks. The only realistic way to manage this problem is through avoidance. Use measured slope angles and/or specific aspect or terrain avoidance to create a larger than normal margin of safety.

Avalanche Discussion

* A deep slab avalanche with a crown height estimated at 4 feet was remotely skier triggered yesterday on Mt. Houghton on an E to ENE aspect at approx 10,200'. The party triggered a large collapse just below the ridgetop. Investigation down slope revealed the avalanche crown below a cliff band. The failing weak layer is unconfirmed. An interface at a crust at the base of the recent storm snow is a possibility but uncertain.

* One small human triggered wind slab was reported yesterday from the start zone on the main avalanche path on the ENE aspect of Incline Lake Peak (Mount Rose area).

* Rapid warming conditions were observed yesterday with surface wet snow formation observed on E-SE-S-SW-W aspects. SE-S-SW aspects were effected up into the 9,500' to 10,000' range.

* Three storm slab avalanches likely having occurred on Saturday were noted yesterday in various locations around the Mount Rose area. Two were human triggered and one was a natural. All three were noted to have occurred in the 9,000' to 9,600' elevation range on open E to ESE aspects and well below the ridgetops.

Régions couvertes