Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Human triggered avalanches remain possible today with potential high consequences.  MODERATE avalanche danger exists with possible wind slabs and persistent slab avalanche problems.

 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    In near and above treeline terrain that received the most storm snow yesterday, we will have up to size D2 wind slab avalanches possible today.  Winds have been elevated into the strong to gale force range in the higher terrain over the last 36 hours with locations along the Sierra Crest receiving up to 5'' of storm snow yesterday.  High winds will continue today before decreasing this afternoon.  Newly formed wind slabs will exist and could be human triggered today.

    Look for signs of wind loading: blowing snow, built out cornices, wind scouring along ridges, and wind pillows.  Cornices and wind slabs could be reactive to the weight of a backcountry user.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Large and destructive avalanches remain possible failing on a weak layer of snow buried 2’ deep or more beneath the snow surface.  The Jan 4 weak layer has been showing signs of gaining strength and adjusting to the load of recent storm snow.  Snowpack tests and informal observations have shown improvement with no avalanche activity reported for the last 2-3 days.  While it is becoming harder to trigger this persistent slab, the consequences remain high.  Avalanches associated with this weak layer would be large avalanche events. 

    The places that would be most likely to trigger this weak layer would be:  complex terrain, convex slopes, and shallower snowpack area.  Remote triggering a persistent slab avalanche or a persistent slab avalanche occurring on a slope that has been previously tracked out remain possible.  Assess slopes before you commit to them.  Talk about consequences with your group and discuss what would happen if an avalanche were to occur.  Avoidance continues to be the best strategy to address persistent weak layers.  Pick a aspect where the problem doesn't exist, or ski slopes below 30 degrees with no overhead hazard.

Avalanche Discussion

Observations were submitted from Donner Ridge (Donner Summit area), Elephants Hump (Carson Pass area), and Upper Deep Creek.  Many snowpack tests targeting the Jan 4 weak layer were conducted.  While the facets below the Jan 4 rain crust still exist, they are gaining strength and adjusting to the load of the recent storm slab.  Many ECT's and PST's targeting this layer indicated that propagation was not likely.

Persistent slab avalanches have not been reported since Sunday.

Moderate wind transport was observed on Elephants Hump with strong to gale force SW winds moving moderate amounts of existing snow.

Regions covered