Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
View on map

Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
Open full map
Out of date — this forecast expired 12 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

For much of this morning, avalanche danger remains LOW for all elevations and aspects. Following the onset of precipitation, avalanche danger will rise to MODERATE danger on all aspects on slopes 35 degrees and steeper during the afternoon and evening hours. Avalanche danger will further increase to CONSIDERABLE danger in these same areas during the overnight hours. Human triggered avalanches will become likely and natural avalanches possible as high intensity precipitation occurs tonight and tomorrow morning.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    For areas above 8,000', the combination of new snow and gale force winds will create new wind slabs in wind loaded areas both above and below treeline. Slab development will be focused on NW-N-NE-E-SE aspects, but possible in isolated areas other aspects as well due to swirling winds. Areas of wind slab instability are expected to form late this afternoon and become larger and more widespread during the evening and overnight hours. 

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    In areas where rain falls on snow, loose wet avalanches will become possible. In most areas below 8,000', free water drainage from the snowpack is well established and wet loose instability is expected only in areas where temporarily lower snow levels deposit a few inches of new snow that then receives rain as snow levels rise back towards 8,000'. This same type of instability scenario is expected in areas above 8,000' where snow levels temporarily rise and deposit rain on top of either new snow or old low density near surface snow layers. Natural or human triggered wet loose avalanches will become possible this afternoon through tomorrow on all aspects, but generally require steeper slopes with slope angles of 37 degrees or greater.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Wet slab avalanches will become possible as the storm progresses mainly above 8,000' in areas where rising snow levels deposit rain on top of new snow that sits on top of an old snow bed surface. Whether a loose wet or wet slab avalanche occurs in this case will depend on the presence or absence of weak layers within the new snow. If no significant weak layers exist within the new snow, loose wet is more likely. If a significant weak layer forms within the new snow or bonding to the old snow surface is poor, then wet slab avalanches will be possible.

Avalanche Discussion

Observations made yesterday on Red Lake Peak (Carson Pass area) and on Mt. Judah (Donner Summit area) fell inline with other recent observations from around the forecast area indicating that the existing snowpack is generally in good condition to handle new loading from rain and snow. Free water drainage from the snowpack is well established in the vast majority of areas below 8,000'. Near surface layers consist of a mix of well established melt-freeze on SE-S-SW aspects and a well bonded mix of crusts, rounds and rounding facets on W-NW-N-NE-E aspects. On some of these more northerly aspects rain and melt-freeze crusts are at the snow surface and in other areas they are buried several inches down. Some NW-N-NE aspect locations hold a notable layer of lower density rounding facets below the thickest rain crust in the upper third of the snowpack. This layer has been a focus for monitoring during the month of January and it has not shown any signs that it will be problematic during the upcoming storm cycle.

A poor to decent snow surface refreeze is expected to have occurred last night due to cloud cover and above freezing air temperatures.

Regions covered