Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

Additional snow and wind today will increase the chances of avalanches.  Large destructive avalanches continue to be a concern with weak sugary snow buried deep in the snowpack.  CONSIDERABLE avalanche danger exists at all elevations due to wind slabs and persistent slab avalanche problems.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    Strong winds have been blowing snow since yesterday afternoon throughout most of the forecast area.  Winds have already increased this morning to gale force with 2 to 5'' of new snow expected today.  Wind slabs could be multiple feet deep and reactive to triggering.  Human triggered wind slab avalanches will be likely today with natural wind slab avalanches possible in the most wind prone areas.

    Look for active blowing snow, cornice formation, wind pillows, and ridgeline scouring.  Avoid run out zones under large cornices and steep wind loaded terrain.  The possibility exists that wind slabs could form over areas that have the buried Jan 4 weak layer.  This setup would make for much deeper avalanches with severe consequences.  Make a travel plan that avoids these areas of concern. 

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    A weak layer of faceted snow exists buried 2 plus feet deep below the snow surface.  This layer continues to produce unstable snowpack test results and show signs of being reactive with whumpfing and collapsing in many areas of the forecast region.  The weak storm forecasted for today will bring 2 to 5'' of additional snow and wind to our area.  The weak layer has been slowly adjusting to the weight of the recent storm snow and reported avalanche activity has begun to taper off.  This additional load of new snow and wind blown snow could tip the balance and make avalanches easier to trigger today. 

    Avalanches associated with this persistent slab problem would be large and mostly unsurvivable.  Recent avalanches on this layer have ranged from 2’ up to 8’ deep.  These avalanches could be remotely triggered, involve a large amount of snow, and have wide propagation.  This problem exists in near and below treeline areas, places that most folks equate with safer backcountry terrain.  The only effective management strategy for persistent slabs is avoidance.  Pick a different aspect where the persistent problem does not exist, or travel on slopes well below 30 degrees in steepness which are not connected above or to the side of avalanche terrain.   

Avalanche Discussion

A recent avalanche was reported from the Incline Lake Peak area that occurred yesterday (Mt. Rose area).  The avalanche was just below the ridgeline and had relatively wide propagation.  It was thought to be a wind slab, but additional information was not possible and the trigger is unknown.  This area has been heavily skied since Friday.   

Multiple observations were reported from Silver Peak (Pole Creek area).  Consistent snowpack test results pointed to propagation being likely if the Jan 4 weak layer could be triggered.  A significant whumpf was experienced while doing snowpack tests in the vicinity of a recent rider triggered avalanche that occurred over the weekend.

Observations from Stevens Peak (Carson Pass) and Horse Canyon (Bear Valley) showed the Jan 4 layer gaining some strength with not as reactive snowpack test results.

Snow transport from moderate to strong winds were reported from multiple areas starting midday.  Available snow for transport exists along many ridgeline areas.

Regions covered