Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Human triggered wind slab avalanches will be possible today.  MODERATE avalanche danger will exist in near and above treeline areas due to wind slabs with LOW avalanche danger in below treeline terrain.  Avalanche danger is expected to increase dramatically tomorrow.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Gale force SW winds yesterday transported large amounts of new and existing snow.  Winds have decreased somewhat, but are still in the moderate to strong range and capable of moving additional snow.  Winds will pick back up to gale force this afternoon and through the night ahead of our next storm.  Lingering wind slabs will be possible today in near and above treeline areas.  Wind slab avalanches that are multiple feet deep could be human triggered today.  

    Look for active wind loading or signs of previous wind loading.  Wind scoured terrain down to firm crusts exist on most all exposed ridges and high points.  Recently deposited wind pillows are below ridgelines and extend far downslope.  Manage terrain and avoid exposure below large cornices and steep wind loaded areas.   

Avalanche Discussion

Observations were received yesterday from Silver Peak (Pole Creek area), Rubicon Peak (West Shore area), and Tamarack Peak (Mt Rose area).  Strong to gale force SW winds with intense active wind loading was experienced at all locations.  Small cracking in wind loaded terrain occurred at all locations, but limited other signs of instabilities existed.  Snowpack tests along with informal observations showed some of these newly forming wind slabs to be stubborn or unreactive to triggering.

The Jan 4 rain crust with weak faceted snow was found on Rubicon Peak and Silver Peak.  On Silver, localized cracking occurred down to the Jan 4 rain crust with the addition of 3'' of new storm snow.  This was thought to be an indication of the weakness of this faceted snow/rain crust.  With a larger load forecasted for Thursday, there is potential that this weak layer could fail.

 

Photo: Cracking through recent storm snow down to the Jan 4 rain crust in wind protected below treeline areas.  Silver Peak.

A large winter storm is forecasted to hit the forecast area Thursday morning.  We have been monitoring the Jan 4 rain crust and weak faceted snow that has formed above and below this crust.  It has been found on NW-N-NE-E aspects in below treeline and near treeline areas throughout the forecast region.  Some signs are showing that these layers could fail under additional load tomorrow as a large storm impacts our area.  Failure of this layer could make for larger and wider storm slab avalanches.  These storm slab avalanches could be remotely triggered, occur mid slope or in below treeline terrain, and potentially be much larger than anticipated.  These avalanches could exist outside of our standard start zones that are not associated with our "normal" avalanche terrain. 

Regions covered