Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Sat
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Out of date — this forecast expired 3 years ago.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

You could trigger an avalanche today that fails 1 to 3 feet deep in locations where a slab of recent new snow sits on top of weak old snow in the lower half of the snowpack. Carefully assess the snowpack before committing to avalanche terrain, especially in and adjacent to shaded areas. Signs of instability are becoming less obvious in some areas, making it easier to get caught by surprise in spots where instability lingers.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    The distribution of this avalanche problem around the forecast area appears to be narrowing. It remains most prominent along the eastern side of the forecast area (Carson Range) above about 8,300' where indicators of instability are reported daily. Substantially fewer signs of instability have been observed along the Sierra Crest in terrain up to 9,000'.

    A persistent slab problem on a decreasing trend presents a challenge that has fooled many seasoned backcountry travelers in the past. Signs of instability become less obvious and less frequent, confidence builds, and then an avalanche is triggered unexpectedly. 

    Given the nature of this avalanche problem, I won't be surprised if an avalanche occurs on a slope that already has numerous tracks on it. Areas in and around shaded terrain remain suspect. You can use different aspects or lower angle, non-avalanche terrain to avoid this avalanche problem.

Avalanche Discussion

Weak faceted (sugary) snow crystals linger in the lower half of the snowpack on many NW-N-NE aspects above 8000 ft. The moisture content of this weak snow has increased, especially below 9,500'. We received one report of basal facets remaining dry post-storm at 9,800'. In the Carson Range where the weakest snow was reported before the last storm, these moist to wet facets continue to fail in snowpack tests, and slope-scale snowpack collapses were reported on Tuesday and Wednesday. More time is needed before the persistent slab problem fully goes away despite the increases in weak layer moisture content.

Snow surface warming has occurred over the past two days across all aspects. At some point, there will be a new crust that forms on the snow surface up to at least 8,300' and potentially higher in some areas due to recent fog.

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

Regions covered