Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

People might still trigger avalanches that break on old, weak snow buried 1 to 3 feet below the surface. Since obvious signs of unstable snow have decreased, avalanches could come as a surprise in an area of seemingly stable snow. Carefully assess the snowpack before venturing into avalanche terrain, especially in cold, shaded areas.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Weak sugary snow (facets) still lurks below more consolidated snow (a slab layer) on many northerly-facing slopes in the forecast area.  Even though no whumpfs, collapses or other obvious signs of unstable snow have been reported since 12/20, snowpit tests keep producing unstable results daily. Hot spots for unstable test results include the mountains east of Lake Tahoe above about 8300 ft and areas along the Sierra Crest above about 8700 ft. However, some tests at lower elevations have also yielded unstable results.

    Without obvious signs of instability, it is easy to get lured into a false sense of security and assume slopes are stable. Still, people may be able to trigger a persistent slab avalanche if they happen across a weak spot (trigger point) hiding in areas of seemingly stable snow. An unexpected avalanche may represent the first and only clue of an unstable slope.

    Traveling on slopes where the weak layers do not exist or in lower-angle, non-avalanche terrain can help reduce your chances of getting surprised by this problem.

     

     

Avalanche Discussion

Extended periods of clear weather and a shallow snowpack have left various weak layers on the cold, northerly aspects that do not see much sun this time of year. Facets exist near the bottom of the snowpack, on the surface, or near/between crusts. Recent warm weather has allowed the weak, faceted (sugary) snow to start clumping together in some areas. In other places, the weak layers remain dry and loose. In general, the snowpack gets weaker as elevation increases. People triggered slope-scale snowpack collapses on 12/19 and 12/20, and snowpit tests continue to produce unstable results on a daily basis. This persistent slab problem may linger for some time or reactivate in future storms.

Warm weather and fog have left crusts on the snow surface up to 8,300 ft, potentially higher in some areas.

The snowpack has become more usable, especially above 7,500 ft. There are still rocks to hit and open creeks to deal with, but not as many as there were before this last storm.

Regions covered