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

Early this morning, avalanche danger remains LOW for all elevations and aspects. Following the onset of snowfall, avalanche danger is expected to increase to CONSIDERABLE during the afternoon hours. Wind slabs and storms slabs are expected as the main avalanche problems.  Especially in areas that held snowcover prior to today's snowfall, natural and human triggered avalanches will be possible on slopes 35 degrees and steeper. The areas of greatest instability area expected near and above treeline on NW-N-NE-E aspects.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Increasing southwest ridgetop winds began redistributing old snow on the ground yesterday. The combination of new snow and ongoing winds today will rapidly add depth to newly formed wind slabs. The majority of wind slabs are expected to form near treeline and above treeline on NW-N-NE-E aspects. Some smaller wind slabs may form in cross loaded areas on SE-S-SW-W aspects as well. Wind slabs are generally easy to identify and avoid. Look for areas of blowing snow, winds pillows, and cornice formation. Wind slabs tend to have fairly distinct top and side boundaries.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    In many areas, new snow today will be deposited on top of near surface faceted snow crystals, especially on NW-N-NE aspects. In heavily shaded open areas, these near surface facets are fairly weak and sugary. The storm slab avalanche problem is most likely be found today in wind protected areas where new snow amounts approaching 1 foot are deposited on top of weak near surface facets. Storm slab boundaries are often not as distinct as wind slab boundaries. Storm slabs are dependent on continuity of a weak layer either at the old/new snow interface or within the new snow. This differs significantly from wind slabs that are dependent on wind drifted snow. Storm slabs with a significant weak layer at the old/new snow interface have greater potential to wrap around corners and can more easily be triggered from very low on a slope. Choose islands of safety well and continually consider the consequences of triggering from near the bottom of a slope.

Avalanche Discussion

Observations made over the past several days in the Mount Rose, Donner Summit, and Carson Pass areas have indicated that significant melt has occurred on the sun expose E-SE-S-SW aspects, especially below 9,000'. NW-N-NE aspects have remained cold and hold a faceted snowpack ranging from 8 to 24 inches deep in wind protected areas. Snowpack depth tends to increase with elevation and is generally only a few inches deep below 7,300'. Faceted snowpack layers have been observed at all heights within the snowpack above 7,700' on NW-N-NE aspects. The degree of anchoring and degree of weakness from faceting varies widely from one location to another. With the existing snowpack fairly shallow, quick hand pits have been a good tool for searching out strong cohesive snow over weaker somewhat sugary snow in recent days.

Regions covered