Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
5 · Extreme
Treeline
5 · Extreme
Below
5 · Extreme
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Highlights

Natural and human triggered avalanches are certain today due to the significant amount of rain on snow expected below 9300 ft. and heavy wet snow loading above 9000 ft. Large, deep, destructive wet slab, deep slab, and wind slab avalanches will occur today as well as loose wet avalanches. Avalanches could run farther than expected and involve almost the entire snowpack. Avoid travel in or near avalanche terrain or runout zones today. EXTREME avalanche danger exists at all elevations. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Certain
    Size
    3

    1.5 to 3.5 inches of rain in the last 24 hours combined with an addition 3 to 5 inches of rain forecasted during the day today and another 1-3 inches of rain in some areas tonight will add a huge load to the snowpack. This rain will also weaken the snowpack as it melts the bonds holding the snowpack together. The combination of significant loading, weakening, and rapid warming means that natural and human triggered wet slab avalanches will be very likely to certain today. These avalanches could occur on any aspect, run farther than expected, and could be large and destructive involving most of the snowpack especially in areas where the deep slabs mentioned below exist. Wet slab avalanches can start and run on less steep slopes. In addition to wet slab avalanches, widespread loose wet avalanches should also occur today. 

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    3

    Heavy rain and snow will add a very large amount of weight to the snowpack and make it easier for the facets near the 12/15 rain crust to fail. Natural and human triggered deep slab avalanches due to the failure of this layer are very likely to certain today on W-NW-N-NE-E aspects at all elevations. These avalanches will be large, very deep, and destructive. They could also run much farther than expected. 

    Deep slabs are unpredictable. Remote triggering with large propagation into any connected terrain remains possible. Ski tracks on a slope will not be an indicator of stability and steep trees will not be a safe zone. Avoiding any terrain where this problem might exist represents the wisest choice for today. Deep slabs can occur on less steep slopes and any slopes steeper than 30 degrees are suspect. 

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    3

    Above snow line where the precipitation falls as snow, strong southwest winds and heavy wet snow will keep adding to the wind slabs that started forming yesterday. Natural and human-triggered large, deep, destructive wind slab avalanches are very likely today on wind loaded slopes. These wind slab avalanches could also step down and become the deep slabs mentioned above.

Avalanche Discussion

Freezing levels rose much faster than expected yesterday and rain started falling up to 9000 ft. in some areas by mid-day. Reports of loose wet avalanches occurring around 9:30 am. In the Tamarack Peak area new snow accumulation and strong winds had formed 6-18 inch wind slabs and huge cornices above wind loaded slopes by mid-day. 2 wind slabs that failed during the morning when cornice pieces fell onto the slopes below them were observed along the far east ridge of Tamarack Peak. Hand pits and other observations showed that the heavy new snow was resting on top of a lighter layer of old snow. Ski cuts and kicks on wind loaded test slopes produced limited cracking. Active wind loading continued in this area all day. 

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