Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

A storm today will bring additional snow and continued strong winds to our area.  Wind slab avalanches will be likely in near and above treeline terrain.  Deep persistent slab avalanches will remain possible and could produce large avalanches failing on weak layers deep within the snowpack.  CONSIDERABLE avalanche danger exists in near and above treeline areas, with MODERATE avalanche danger in below treeline terrain.

Avalanche problems

  • Wind Slabs

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

    Continued gale force SW winds along with additional storm snow today will allow for development of new and larger wind slabs.  These wind slabs will exist on NW-N-NE-E-SE aspects in near and above treeline areas.  Previous wind slab avalanches have been occurring on almost a daily basis and that is expected to increase today with the addition of new snow and continued winds.  Areas that receive the higher end storm snow amounts today will have larger and more reactive wind slabs.  

    Look for areas of blowing and drifting snow.  Terrain near and below cornices and wind pillows will be most suspect for wind slab avalanches.  Make a plan to move around these areas of concern when traveling in the backcountry. 

    Skier triggered wind slab avalanche Sunday on Donner Peak, Donner Summit area.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Deeply buried weak layers in the snowpack continue to present an avalanche concern.  Human triggered deep persistent slab avalanches remain possible on NW-N-NE aspects at all elevations.  The last avalanche associated with this problem was triggered on Sunday afternoon on Waterhouse Peak in the Luther Pass area.  This avalanche produced a 2.5 to 4' crown line that ran through dense trees and rocks.  Avalanches associated with this problem could be large to very large in size involving part or most of the existing snowpack.  These avalanches could be remotely triggered with potentially wide propagation.  Most of the areas of concern for this deep slab avalanche problem exist on the Eastern side of the forecast region where a weak and shallow snowpack existed before the recent large storm event.  This includes portions of the Carson Range on the NE, E, and SE sides of Lake Tahoe and locations east of the Sierra Crest in the Luther Pass, Carson Pass, and Ebbetts Pass areas.

    Managing a deep persistent slab avalanche problem can be difficult.  There may be very limited or no signs of instability until an avalanche occurs.  Options could be to avoid areas with previous avalanches associated with this deep slab problem that had a shallow and weak snowpack before the storm.  Other strategies would be to utilize low angle terrain on NW-N-NE aspects with no connected steeper terrain above or to the side, or use other aspects to recreate on where this avalanche problem is not a concern.   

    2.5 to 4' crown from a skier triggered deep persistent slab avalanche on Waterhouse Peak on Sunday afternoon.

Avalanche Discussion

*  A deep slab avalanche that occurred on Waterhouse Peak (Luther Pass area) on Sunday afternoon was investigated yesterday.  Report here.

* Reports throughout the forecast area yesterday of gale force SW winds transporting snow.   

* Evidence of widespread avalanche activity continues to be reported from during the last storm cycle both above and below treeline in both upper and mid slope start zones on NW-N-NE-E aspects. Many filled in avalanche crowns with wide propagation consistent with persistent slab avalanche continue to be reported. 

Regions covered