Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

As a storm system moves through the region today, avalanche danger will gradually increase with peak instability expected during the late afternoon and evening hours. An uncommon wind direction during the majority of today's snowfall event will create a different distribution of accumulating wind drifted snow than what normally occurs. New snow falling on weak snow at the old surface may enhance instability in some areas.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Winds start out from the SW this morning which is the common direction during snowfall events.  Winds will shift to the NE today as the cold front passage occurs. It is expected that winds out of the NE will accompany 75% to 90% of the snowfall that occurs today. This will create a less common distribution pattern for blowing and drifting snow that forms into new wind slabs during the storm today. Anticipate the gradual development of new wind slabs in near treeline and above treeline areas across SE-S-SW-W-NW-N aspects.

    Gradually increasing instability today will lead to areas of unstable snow becoming most widespread during the late afternoon and evening hours. Look for and identify where wind drifted snow is accumulating and expect to find it in less common areas due to the NE wind direction. Use clues such as blowing snow, freshly formed pillows of wind drifted snow, and snow surface cracking to identify where unstable snow may exist. Consider avoiding avalanche terrain where signs of potentially unstable snow are present.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    By the afternoon and evening hours, areas of unstable snow are expected to form in wind protected areas near treeline and below treeline. In any locations where new snow is deposited on top of surface hoar, avalanches may be easier to trigger and fail with wider propagation. Shaded, wind protected terrain on NW-N-NE aspects is the most likely but not the exclusive location for surface hoar to have escaped destruction and persisted to burial by today's snowfall.

    Any wind protected areas where snow surface cracking is easily triggered are suspect for storm slab avalanches. Consider moving to low angle slopes and avoiding exposure to avalanche terrain in areas where snow surface cracking is observed. Keep in mind that instability is expected to increase as the day progresses. Stability may change greatly on a specific slope from the morning to the afternoon. Route plan accordingly and reassess terrain as the storm progresses.

Avalanche Discussion

  • Surface hoar destruction was observed yesterday in several locations due to warming air temperatures. Surface hoar that contributes to increased instability is expected to linger in a few shaded and wind protected areas.
  • The deeper snowpack is in good condition to handle new snow loading. Avalanche activity that occurs today is expected to fail at or above the old/new snow interface.

Regions covered