Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Strong winds will continue to transport snow and form slabs of wind-blown snow in exposed areas.  Storm slabs will develop this afternoon as high intensity snowfall begins to enter our area.  Exercise increased caution and consider avoiding avalanche terrain in areas where signs of unstable snow are present. 

A large Atmospheric River storm will enter our area later this afternoon through Friday evening.  Avalanche danger will increase quickly to HIGH tonight with widespread avalanche activity expected during this period.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2.5

    Strong to gale force southwest winds continued from yesterday and will intensity this afternoon along with additional snowfall.  Large amounts of snow available for wind transport exists with continued wind slab development on NW-N-NE-E-SE aspects in near and above treeline areas.  Wind slabs could also form in some areas in below treeline terrain due to the strong winds.  These wind slabs will continue to remain reactive today with natural wind slab avalanches possible.

    Look for blowing snow, cornice formation, wind pillows, and snow surface scouring as clues to where these wind slabs are forming.  Snow surface cracking and denser snow over less dense snow will also indicate the presence of wind slabs.  Avoid steep wind loaded terrain and areas below cornices when signs of unstable snow exist.

  • Loose Wet

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

    Intense solar radiation this morning from sunny skies along with increasing temperatures will make wet loose avalanches possible.  Roller ball and pinwheel activity will occur quickly this morning with the potential for larger wet loose avalanches occurring.  Longer slopes will have the potential for larger and longer running wet loose avalanches entraining some of our recent storm snow.  As rain on snow occurs later this evening, this problem will become more widespread and include all aspects. 

  • Storm Slabs

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

    Storm slab instability occurred yesterday with high intensity snowfall in the morning.  Additional storm slab formation is expected this afternoon when snowfall intensity increases with the approaching storm.  In addition, this storm will be warmer than our previous cold temperatures and snow that we have been receiving recently creating a heavier layer on the surface.  These upside down conditions could cause this new layer of snow to overload the previously lighter surface snow and create storm slab avalanches.  This avalanche problem will further deteriorate as the storm intensifies and warms into the evening.  

     

Avalanche Discussion

  • SW winds have remained ongoing with drifting of new snow observed daily in near treeline and above treeline terrain.
  • Several wind slab avalanches size D1 to D2 occurred over the last 2 days in various portions of the forecast area.
  • Reports of snowpack collapse and whumpfing were received Monday from two separate locations on southerly aspects in the Mount Rose zone. Isolated whumpfing was again reported yesterday in this zone, likely on the March 4 crust/facet layer. Other observations targeting this layer on Tuesday did not reveal signs of instability.

Regions covered