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

Slabs of wind drifted snow at upper elevations and sluffs of wet snow at lower elevations are possible today. New loading on the persistent weak layer of crust and sugary faceted snow means that higher consequence avalanches may also be possible today. Avalanche danger is MODERATE for all elevations.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    New slabs of wind drifted snow should have started to form on leeward aspects at upper elevations during the night. These wind slabs should become slightly larger and more widespread as more snow accumulates and snow levels fall today. Human-triggered wind slab avalanches will be possible today. The largest and most fragile wind slabs will exist on wind-loaded NW-N-NE-E-SE aspects in near and above treeline terrain. Large cornices also exist above many wind-loaded slopes.

    Identify where wind slabs may exist by looking for signs of wind-loading like blowing snow, snow drifts, cornices above a slope and other wind created features. Use this information to avoid the areas where these fragile wind slabs may exist.  

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Recent data has indicated increased variability in the strength of the Jan 4th persistent weak layer. In some areas, it has gained strength. In other areas, it remains weak. Avalanche activity has not been reported on this layer for several days. The rain and snow from last night and today may add enough weight to the snowpack to reactivate this weak layer of sugary snow (facets) in some places today. This layer is most prevalent on the near and below treeline NW-N-NE-E aspects. It is typically buried 1 to 2 feet below the snow surface except in a few areas where drifted snow has buried it much deeper. Some human triggered avalanches may be possible on this layer again today.

    Any avalanches that do occur on this layer would have severe consequences. Due to these consequences and a high degree of uncertainty surrounding this layer, conservative terrain selection is recommended anywhere you suspect this layer exists.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Wet snow and rain on snow at lower elevations mean that small sluffs of wet snow may be possible today below 7500 ft. These loose wet avalanches should become less likely as temperatures cool off throughout the day. 

Avalanche Discussion

Observers reported more variable results on the Jan 4 persistent weak layer. Snowpit tests yielded unstable results on Relay Peak and Stevens Peak. MIxed results (some unstable, some not unstable) occurred on Slide Mountain, Yuba Pass, and near Independence Lake. Non-reactive tests occurred on Powderhouse and in Hope Valley. Overall data has indicated that this layer has become highly variable. It remains weak in some areas but has gained strength in others.

Firm rain crusts gave way to wet snow and breakable crusts across the forecast area yesterday. Spring-like conditions were reported on sunny slopes by yesterday afternoon in the Mt. Rose area and the Hope Valley area. One party reported a small loose wet avalanche on Mt. Houghton. Another party saw debris from a recent cornice collapse on Donner Summit.

Regions covered