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

Pockets of MODERATE avalanche danger exist at all elevations on NW-N-NE aspects on slope steeper than 32 degrees that held snowcover prior to the recent snowfall. For all other areas, avalanche danger is LOW. Persistent slabs and wet slabs remain an ongoing avalanche concern.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Wet slab avalanches remain possible today in near treeline and below treeline terrain on NW-N-NE aspects up to around 9,800'. Weak layers of wet faceted snow located below the old/new snow interface continue to show the ability to allow fractures to propagate in some areas. The potential for increasing avalanche size increases in relation to elevation as depth of both new and old snow increases. The thickest overlying slabs of new snow exist at the higher elevations. As wet faceted snow continues to refreeze, danger associated with this avalanche problem will continue to decrease.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    In areas above 9,500' to 9,800', rain did not percolate full depth through the faceted old snow layers. Persistent slab avalanches remain possible on slopes that represent the highest elevation near treeline and below treeline terrain within the forecast area. In these areas, weak layers of well developed facets and depth hoar remain problematic. Danger associated with this avalanche problem will decrease at a slower rate than the wet slab problem mentioned above.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    Lingering wind slabs may remain unstable on NW-N-NE aspect above treeline terrain and along sparsely treed ridgelines. Medium size slabs will exist at higher elevations where greater amounts of new snow accumulation occurred.

Avalanche Discussion

Observations made yesterday on Mt. Judah and Castle Peak in the Donner Summit area and on Mount Rose proper indicated that the snowpack is continuing to slowly gain strength following the recent rain and snow event. Evidence of rainfall from January 29 is visible in the snowpack up to a little over 10,000' on Mount Rose. In locations observed over the past two days, rain appears to have percolated full depth through the old snow layers up to an elevation of around 9,500' to 9,800'. Rain wet layers are in the process of draining and refreezing. It will likely take a few more days for full refreeze of rain wetted layers to occur.

Yesterday while ascending Mount Rose, two skier triggered collapses with audible whumphing sounds occurred in below treeline terrain on an NE aspect between 9,000' and 9,300'. The failure layer was wet facets below the new snow. In other areas yesterday, snowpit tests from each of the observed locations produced variable results on wet facets below 9,000' and on dry facets above 9,900'. Indications that human triggered avalanches could occur ranged from unlikely to likely.

Regions covered