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 on all aspects and elevations.  As daytime warming begins, pockets of moderate avalanche danger will form on E-SE-S-SW aspects at all elevations due to loose wet avalanche problems.  Avalanche danger will remain low on W-NW-N-NE aspects at all elevations.  

Problèmes avalancheux

  • Loose Wet

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

    Air temperatures at 6am above 7000' were well above freezing and ranged from the mid 30's to low 40's.  Winds have shifted direction from the E to the S-SW and should be light to moderate in speed today above 7000'.  Radiational cooling under clear skies has helped to marginally refreeze the snow surface on these solar aspects.  Although any refreeze that has occurred should be thin and short lived as daytime warming occurs.

    The snowpack on E-SE-S-SW aspects is made up of 3-4'' of wet surface snow with colder, dryer, snow below that, on top of  rain crust.  The thin surface refreeze should go away and start to loose supportability within the morning hours.  Human triggered wet loose avalanches will become possible on slopes steeper than 35 degrees.  Most of these loose wet avalanches will be in the form of human triggered pin wheels or roller balls but in some cases could be large enough loose wet avalanches to injure or bury a backcountry user.  In isolated cases, these loose wet avalanches have entrained the dry snow below the wet surface snow and have slid on the buried rain crust and caused much larger and destructive avalanches.

    Timing will be important if you plan to travel on solar aspects today.  Avoid steep solar aspects when daytime warming occurs.  Current roller balls or pin wheels will be an indication that the snow surface has lost supportability and strength.  Hand pits and boot penetration may help give clues to upper snowpack strength.  

Avalanche Discussion

Recent observations over the last several days show similar snowpack characteristics throughout the forecast region.  Warm overnight temperatures have created weak melt freeze conditions on most E-SE-S-SW aspects at all elevations.  Loose wet instabilities have formed by mid morning on these aspects due to daytime warming and a weak overnight refreeze.  Most instabilities have been in the form of human triggered pin wheels or roller balls, although some larger loose wet avalanches have occurred.

On Mt. Lola (Independence Lake area) wet snow existed by 9:15am on east aspects.  Above 8000', east winds have scoured most exposed N-NE-E aspects and helped to limit any wet snow instabilities.  On solar aspects, test pits found several inches of wet surface snow on top of colder, dryer snow on top of rain crust.  Snowmobile cuts on test slopes failed to produce any loose wet instabilities. 

Régions couvertes