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

This morning the avalanche danger is LOW. As the day warms up, pockets of MODERATE danger will quickly form on E-SE-S-SW aspects due to the possibility of loose wet avalanches. Some small loose wet issues may form on near and below treeline N-NE aspects in isolated or extreme terrain. Small human triggered roller balls, pinwheels, and point-releases should comprise most of the loose wet activity, but some loose wet avalanches could involve enough snow to cause problems for backcountry travelers. 

Problèmes avalancheux

  • Loose Wet

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

    While some refreeze may have occurred last night due to heat radiating out into the night sky from the snowpack, the overnight temperatures well above freezing and the scattered cloud cover should mean that last night's refreeze was weak. Continued warm temperatures and some sunshine should quickly melt through last night's weak refreeze leaving a deep layer of wet snow on the surface even though the light to moderate winds and partly cloudy skies should keep slopes a little cooler today. The partly cloudy skies may also allow the wet snow to spread onto some of N and NE facing slopes as the clouds prevent radiational cooling and act as a blanket that can help distribute warmth to non-sun-exposed areas. Human triggered loose wet avalanches will become possible today on slopes 35 degrees and steeper where wet snow forms.

    The majority of wet snow instabilities should form on sun-exposed E-SE-S-SW aspects, but some may also form on near and below treeline N-NE aspects. Small roller balls, pinwheels, and point release avalanches should comprise most of these loose wet instabilities, but some of them could entrain enough snow to cause problems for backcountry travelers. Stepping off your equipment and sinking into wet snow above your boots can indicate that enough wet snow exists on a slope for a loose wet avalanche problem. Small loose wet instabilities like roller balls and pinwheels often foreshadow larger loose wet snow issues as well. These clues or other signs of wet snow issues mean that it is time to find a more frozen slope or switch to a different afternoon activity.

Avalanche Discussion

Yesterday observations from Negro Canyon and Castle Peak (Donner Summit area) showed firm melt freeze crusts and exposed rain crusts on the sun-exposed E-SE-S-SW aspects during the morning. By mid day some corn snow had formed above these crusts. Observations later in the day on Becker Peak (near Echo Summit) showed that the melt-freeze crusts on the SE-S-SW aspects became unsupportable by 1 pm, and shin deep wet snow existed on those aspects by that time. Loose wet avalanches also occurred around Emerald Bay yesterday with one of them running down an E aspect and depositing about 3 ft of debris onto the road. This slide occurred between 11 am and 3 pm. On the northerly aspects observers in Negro Canyon found some lingering patches of soft cold snow in sheltered areas. On Becker Peak the snow on the northerly aspects had started to become wet and sticky and allowed some small human triggered roller balls and pinwheels to occur by 2 pm. Snowpit data and general observations from both Negro Canyon and Becker Peak did not reveal any signs of instabilities buried in the snowpack. 

Régions couvertes