Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Pockets of MODERATE avalanche danger may exist near and above treeline on NW-N-NE-E-SE aspects due to lingering unstable wind slabs on slopes 35 degrees and steeper. In wind protected areas below treeline and in wind scoured areas near and above treeline, avalanche danger is LOW.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Strong to gale force ridgetop winds over the past 48 hours redistributed snow on the ground following the last weekend's storm cycle. Windward areas are becoming scoured and little to no snow remains available for continued wind transport despite ongoing gale force ridgetop winds. Previous wind loading and subsequent wind slab formation has been observed near and above treeline on NW-N-NE-E-SE aspects. Areas above 8,400' that did not receive any rain on Feb 9 had significantly more snow available for wind transport. Pockets of unstable wind slabs 8 inches to 3 feet deep may be encountered today with human triggered avalanches remaining possible.

Avalanche Discussion

The northern portion of the forecast area received a significant mist and light/moderate rain event yesterday up to at least 10,000'. At the same time, the southern half of the forecast area experience mostly cloudy to sunny skies with increasing amounts of sunshine towards Ebbetts Pass.

Observations made yesterday on Tamarack Peak (Mount Rose Backcountry) noted wet surface snow with the top 1.5 inches wet at 8,600' and 0.5 inches of wet surface snow above 9,000'. Wind slabs at treeline were dense and provided no obvious signs of instability in response to slope cuts. Snowpit data collected below treeline to examine basal facets revealed rounding of large grain facets and old depth hoar in the lower 16 inches of the snowpack on a NE aspect at 9,400'. Snowpit tests indicated that triggering collapse of this weak layer is very difficult and that once collapsed, significant propagation is unlikely. Similar wet snow surface conditions were noted on Andesite Peak (Donner Summit area) with moderate rain at times and wet surface snow 2 to 3 inches deep.

Observations made yesterday on Stevens Peak (Carson Pass area) revealed similar increasing strength of basal facets. Wet surface snow was limited to the top 2 to 3 inches of the snowpack and created by daytime warming rather than by rain/mist. A significant low density weak layer of recent storm snow was noted below recently formed wind slabs in the area.

Regions covered