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 11 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Early this morning, LOW avalanche danger exists for all elevations and aspects. Pockets of MODERATE avalanche danger will form quickly in response to daytime warming on SE-S-SW aspects at all elevations on slopes 35 degrees and steeper. On W-NW-N-NE-E aspects, avalanche danger will remain LOW with small, isolated human triggered loose wet avalanche activity unlikely but not impossible below 8,000' on slopes 35 degrees and steeper.

Problèmes avalancheux

  • Loose Wet

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

    The snowpack on SE-S-SW aspects remains in a transitional state. Under the relatively weaker and lower angle early February sun, daily melt-freeze cycles have been insufficient to produce corn snow conditions. What exists instead is a few inches of surface wet snow on top of colder, dry, less consolidated remnant storm snow, sitting on top of rain crust.

    Once the thin ice layer of overnight snow surface refreeze is gone, marginally supportable conditions exist and the snowpack structure is conducive to human triggered loose wet avalanche activity. Snowpack failure has been occurring at the interface between the surface wet snow and the colder drier snow below it. In most areas this has manifested as human triggered roller balls and pinwheels. In more isolated areas human triggered loose wet avalanches large enough to bury or injure a person are possible in steep terrain. An incident occurred yesterday on Jakes Peak on the S to SE aspects above Emerald Bay where two skiers were caught and carried in a sizable loose wet avalanche.

    The problematic surface wet snow over drier, colder snow structure is easily identified by hand pits as this structure exists within the top 6 to 8 inches of the snowpack in the vast majority of areas on SE-S-SW aspects. In areas where this snowpack structure exists, avoid travel on slopes steeper than 35 degrees and stay out from under steeper terrain above.

    With 6 am air temperatures above 7,000' in the mid 30s to mid 40s in most locations, snow surface refreeze last night will have been entirely dependent on radiational cooling under clear skies. This superficial refreeze is expected to only be a couple of inches thick in most areas and will melt quickly today.

Avalanche Discussion

A report was received of two skiers involved in a sizable loose wet avalanche yesterday on the S to SE aspects of Jakes Peak above Lake Tahoe's Emerald Bay. Reported details are extremely limited, but both skiers are understood to have been caught and carried. Both escaped burial and significant injuries. Isolated natural loose wet avalanches have been reported in recent days, but as the snowpack has had more time to transition, naturals have become unlikely with human triggering remaining the ongoing problem.

Snowpack observations made and received yesterday from Stanford Rocks (Ward Canyon/Blackwood Canyon area) and from Rubicon Peak (West Shore Tahoe area) indicated that NW-N-NE aspects held a well bonded and well consolidated snowpack. Up to 6 inches of cold unconsolidated surface snow was reported in wind protected areas above 8,000'. On the SE-S-SW aspects near Stanford Rock, any signs of overnight snow surface refreeze were gone by the late morning hours. By noon, 3 to 5 inches of surface wet snow on top of colder, drier, remnant storm snow over rain crust existed within the top 6 to 12 inches of the snowpack. This same upper snowpack structure has been observed on SE-S-SW aspects in numerous locations around the forecast area over the past several days.  

Régions couvertes