Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

MODERATE avalanche danger will exist for most of today at all elevations due to a loose wet avalanche problem. As new snowfall and wind impact the forecast area this evening, avalanche danger will increase to CONSIDERABLE danger near treeline and above treeline due to a wind slab avalanche problem.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    SW winds mixed out air temperature inversion conditions last night allowing for air temperatures to fall below freezing above 8,500'. Snow surface refreeze contributions from radiational cooling were compromised by periods of cloud cover last night. As a result, a weak to decent snow surface refreeze is expected to have occurred last night. Surface refreeze was likely a little better above 9,000'. Periods of sunshine this morning and above freezing air temperatures will create snow surface melt that leads to another round of loose wet avalanche problems. Loose wet avalanches will be possible today on all aspects at all elevations. Avalanche size up to D2 is possible (large enough to bury or injure a person). Increasing cloud cover will temper afternoon melt rates, but sufficient melt is expected this morning to get this avalanche problem going.

    Mid and upper elevation NW-N-NE aspects may see human triggered roller balls as an indication of potential unstable conditions as the recent storm snow continues to transition to corn. Where melt-freeze conditions are well established on E-SE-S-SW-W aspects, focus on monitoring snow surface supportability. Once the snow surface is in melt phase and conditions become marginally supportable to unsupportable, avoid travel in or below avalanche terrain.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    Following the onset of snowfall, a wind slab avalanche problem will develop this evening near and above treeline on NW-N-NE-E-SE-S aspects. Avalanche size up to D2 is expected (large enough to bury or injure a person). Identify areas of wind drifted snow near ridgelines and in gully features. Avoid avalanche terrain in areas where snow surface cracking is occurring. Slopes with cornice features or wind pillows across the upper portion of the slope will become highly suspect.

Avalanche Discussion

* Observations were made yesterday on Stevens Peak (Carson Pass Area). Warming conditions and snow surface melt were observed in this area on all aspects. Recent storm snow on E-SE-S-SW-W aspects was assimilated with the older melt-freeze snow below it up to the highpoint of travel around 9,800'. An intentionally skier triggered loose wet avalanche occurred at noon on a NE aspect at 8,800' where the recent storm snow was entering into melt phase for the first time.

* The high sun angle this time of year is allowing for significant amounts of incoming solar radiation on NW-N-NE aspect terrain that is otherwise well shaded from November through February.

* Snow cover below 7,200' to 7,500' is becoming very thin to nonexistent in many portions of the forecast area. In some locations, snow cover is notably patchy below 8,000'.

Regions covered