Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

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

Points saillants

Triggering a persistent slab avalanche still remains a concern in the backcountry.  Recent heavy storm snow and rain have formed cohesive slabs of snow on top of our shallow and weak snowpack.  Move away from avalanche terrain is you see signs of unstable snow.  If in doubt or faced with uncertainty, choose not to travel in or below avalanche terrain.

Problèmes avalancheux

  • Persistent Slabs

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

    Recent rain and heavy snow have loaded our persistent slab weak layers with signs of instabilities being reported over the last few days.  At lower elevations, these weak layers are gaining strength from being wet and re-bonding into the snowpack.  These layers may still need additional time before they are no longer problematic.  At higher elevations in the forecast area, our faceted snow and depth hoar are still dry and preserved near the base of the snowpack.  These weak layers now have a heavy and cohesive slab on top of them.  Any avalanche involvement would make serious injuries more likely due to our shallow and rocky early season snowpack.

    Obvious signs of instabilities (recent avalanches, shooting cracks, whumpfing sounds, and collapsing) may become less frequent and harder to find today.  Persistent slab avalanches could still occur.  These persistent slab avalanches could be remotely triggered, could fail low on a slope, and could be much wider in size than expected.  Utilizing low angle non-avalanche terrain, not connected to any steeper terrain above or beside, is a great way to manage this avalanche problem. 

Avalanche Discussion

A weak faceted (sugary) snowpack exists on most NW-N-NE aspects above 8000 ft.  Near and below about 8,500', faceted snow exists near buried rain crusts. Above 8,500', the rain crusts gradually disappear, and almost the entire lower half of the snowpack becomes weak faceted snow. The higher you go on wind-protected NW-N-NE aspects, the weaker the snowpack. These weak layers are well developed, with depth hoar found at the base of the snowpack in many areas.  Depending on location, the recent storm has wetted these weak layers up to 8500' to 9000'.  Above 9000', these weak layers remain dry and preserved in some areas.

There is still the potential to hit many obstacles (rocks, logs, open water, bushes, etc.) that are barely covered (or not) by the shallow snowpack. This is especially true in areas below 7,500' and very rocky areas up to at least 8,000'. Anticipate encountering a different snowpack structure and a different set of travel conditions if you are moving from one place to another around the forecast area.

Régions couvertes