Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Fri
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Isolated instabilities continue to exist deeper in our snowpack, mainly on the eastern side of the forecast area.  Rain and high elevation snow occurred yesterday and overnight.  Areas of blowing snow could form slabs of wind blown snow at the higher elevations.  Look for signs of unstable snow and move cautiously around these areas of concern.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Where new snow was deposited yesterday and overnight and snow is available for wind transport, wind slabs could exist.  SW winds have been strong to gale force overnight and will switch to the W and continue today.  Wind slabs will mostly be above 8000-9000' above where most of the rain occurred, depending on location.  In some locations where these wind slabs have formed on top of recently buried surface hoar, wind slab avalanches could be easier to trigger and propagate wider than expected.

    Look for blowing snow, snow available for transport, new cornice formation, and wind pillows as clues to where wind slabs could be forming.  Move around these wind loaded areas with caution.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–3

    The persistent slab avalanche problem that has been with us for most of our season is nearing the end.  Lingering instabilities continue to show weaknesses where a shallow snowpack exists, mainly in the eastern part of the forecast region.  The Jan 2 PWL (buried surface hoar, facets, and/or near crust facets) has become unreactive with no known avalanches occurring since Jan 18.  The Dec 19 rain crust and the basal facet/depth hoar layers continue to exist where the snowpack structure remains shallow and weak.  Unfortunately, this will continue for some time until our snowpack gets deeper and gains additional strength.

    An isolated large avalanche could still occur in areas where the snowpack remains weak and shallow.  On a regional scale, this represents a small portion of the forecast area.  Wide safety margins and best practice travel protocols remain good strategies for backcountry travel.

Avalanche Discussion

Surface hoar formed on W-NW-N-NE-E aspects and was buried by the Jan 24 storm.  High elevation rain is thought to have destroyed most of this surface hoar, potentially up to 8000-9000'.  In higher elevation areas, some of this surface hoar may be slightly buried under a couple inches of snow and preserved for the future.  Where wind drifted snow has been deposited on top of this buried surface hoar, wind slabs may be easier to trigger today.

Firm rain crusts will exist at lower elevations and up to 8000-9000'.  These firm crusts could impact travel today.

Régions couvertes