Lawinenlagebericht

Central Sierra Nevada

Sierra Avalanche Center
Auf der Karte ansehen

Lawinengefahr

Tue
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
Open full map
Veraltet — dieser Lagebericht ist 3 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Heavy new snow and rain on top of buried old, weak snow will create dangerous avalanche conditions today. People could trigger avalanches that break in the old, weak snow or cause avalanches of wet rain-soaked snow. Getting caught would also likely result in serious injury due to the shallow rocky snowpack. If in doubt or faced with uncertainty, choose not to travel in or below avalanche terrain.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2

    Heavy wet snow and rain on top of the existing snowpack and its buried weak layers of rotten, sugary snow will create dangerous and unusual avalanche conditions. Any new snow that falls could form a slab layer on top of the snowpack, especially in wind-affected areas. Rain will add weight to the snow above the weak layers and weaken the snowpack.  While the snowpack structure and weak layers vary by elevation and location, data and observations have shown that NW-N-NE aspects above 8000 to 8300 ft hold the weakest snowpack. The new snow and rain during this storm could push these layers to the breaking point, and human-triggered persistent slab avalanches will likely occur. Getting caught in such an avalanche could have higher consequences due to the shallow rock-infested snowpack.

    Clues like recent avalanches, snow surface cracking, snowpack collapse, or whumpfing sounds can help alert people to unstable, persistent slabs. Sometimes, triggering an avalanche represents the first sign of an unstable slope. People can trigger persistent slab avalanches from a distance or low on the slope, and they can break wider than expected. The consequences, variability, and unusual problems make conservative decisions prudent. If you see any signs of unstable snow or doubt about a slope, play it safe, assume it is unstable, and stick to low-angle, non-avalanche terrain not connected to steeper areas above or beside it.

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Wet snow will likely slide downhill on steep slopes where rain falls on snow during this storm. Wet loose avalanches will likely occur as the upper layers of the snowpack become wet. These could entrain enough snow to push people into barely covered obstacles or knock people over. Some could even involve more snow on long, steep, snow-covered slopes. The rain will also add weight to the snowpack and exacerbate the persistent slab problem mentioned above.

    Wet surface snow, pinwheels, and roller balls indicate unstable wet snow. If you get out in the rain, traveling in lower angle non-avalanche terrain that is not below steeper terrain represents the best way to minimize your exposure to wet loose avalanches.

Avalanche Discussion

A weak faceted (sugary) snowpack exists on most NW-N-NE aspects, especially in areas above 8000 ft, with a few spots holding weak snow down to about 7,400'.  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. Generally speaking, 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.

While no avalanches have been reported on these weak layers, people did trigger collapses that propagated across entire slopes after each of the last two storms. One of these occurred in the Hourglass and one in Broken Glass. The current storms will add more load than either of those previous storms. They will add slabs of heavy, dense snow above these weak layers. The high snow levels will also push people to recreate where the weakest snow exists.  This combination of heavy slabs on top of old, weak snow and increased use is a recipe for serious avalanche incidents.

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.

Abgedeckte Regionen