Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
1 · Low
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 11 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

LOW avalanche danger continues for all elevations and aspects. Small wind slabs are a lingering issue today near and above treeline on NW-N-NE aspects. These wind slabs might remain sensitive to human triggering in isolated areas. Avalanche size is expected to remain too small to bury a person unless highly defined terrain traps are involved. Normal caution is advised.  

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1

    Strong SSW ridgetop winds yesterday created areas of blowing snow and enough wind loading to build small wind slabs near and above treeline on NW-N-NE aspects. Four small skier triggered avalanches were reported yesterday, at least two of which were intentionally triggered. In all cases avalanche size was too small to bury a person (more info below). Winds have shifted more to the S and snow on the ground available for wind transport is diminishing. Wind slabs are expected to be more difficult to trigger today than yesterday in the majority of areas. In isolated areas, triggering may remain easier today due to the presence of surface hoar, large stellar, and/or plate crystals at the weak layer interface. These are uncommon weak layers for this region and will make for more atypical remote triggering and delayed stabilization in any areas where they exist.

    Terrain management to specifically avoid areas of recent wind loading is the wise choice today. Wind pillows, the leeward side of ridges where abrupt changes in snowpack depth occur, and below cornice features are simple ways to identify where unstable wind slabs might exist. More experienced travelers will be able to read micro terrain features, observe snow surface texture and feel slab over weak layer density changes to more precisely determine the boundaries of wind slabs.

Avalanche Discussion

Observations made and received yesterday from Carpenter Ridge (Independence Lake area), Silver Peak (Pole Creek area), and Trimmer Peak (Luther Pass area) all indicated areas of wind loading on NW-N-NE aspects near and above treeline. On Carpenter Ridge, two small wind slab avalanches were intentionally remotely triggered near treeline on N aspect, 39 degree slopes at 8,600'. Crown height ranged from 4 to 12 inches, were 40 to 50 feet wide, with the slab extending 10 to 20 feet down slope. The avalanches ran for about 100 feet and were too small to bury a person. In this area, extended propagation beyond typical wind slab pockets combined with remote triggering pointed towards some potential persistent slab characteristics. Crown and bed surface examination revealed 1 finger hard wind slab on top fist hard near surface facets and the uncommon presence of large flat snow crystals in the form of surface hoar, large stellar, and/or plate crystals at the weak layer interface. On Trimmer Peak a party reported triggering two smaller wind slab avalanches near treeline on a N aspect at 9,300' with crown depths of 2 to 4 inches that were 10 feet wide.

The upper snowpack has remained cold this past week and there is increasing evidence of near surface faceting. In isolated areas, near crust faceting is starting to occur around the Dec 24 rain crust located 6 inches to 2 feet deep in most areas. This crust is absent in isolated areas. Both of these layers warrant continued monitoring for development into potential weak layers in the future.

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