Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
View on map

Avalanche danger

Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
Open full map
Out of date — this forecast expired 9 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Considerable avalanche danger will exist today due to wind slab, storm slab, and deep slab avalanche problems.  Wind slabs will be likely in near and above treeline areas.  Storm slabs and deep slabs will be likely in near and below treeline areas.  Dangerous avalanche conditions exist.  Careful snowpack evaluation, cautious route finding, and conservative decision making are essential today.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Winds slabs will be likely today in near and above treeline terrain on NW-N-NE-E-SE-S aspects.  Strong to gale force SW winds yesterday and overnight have built large wind slabs.  These wind slabs will continue to grow today as winds increase in speed from the W.  Natural and human triggered wind slab avalanches are expected.

    Look for signs of active wind loading; blowing snow, cornice formation, and wind pillows.  Wind slabs could continue to be reactive even if wind speeds decrease.  Snow surface clues can help determine where wind slabs may have formed last night.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    Storm slab avalanches are likely today in below treeline and near treeline terrain on all aspects.  Buried surface hoar has been found in several locations around the forecast area.  This surface hoar has been found in open areas in near treeline and below treeline terrain where winds have not destroyed it.  Buried surface hoar is capable of being remotely triggered and can fail on lower angle slopes.  In addition, storm slabs could also fail on weaknesses within the new storm snow or at the old snow/new snow interface.

    Look for cracking around skis, shooting cracks, or any signs of cohesion within the new storm snow.  These storm slabs will be in wind protected near and below treeline terrain.  Avoid areas that show signs of unstable snow and avoid avalanche runout zones.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    The persistent weak layer that has affected our forecast area for many weeks is now buried 2-4'+ deep below the snow surface.  This deep persistent slab avalanche problem has been found in isolated areas on NW-N-NE aspects in near and below treeline terrain.  This weak layer continues to show unstable snowpack test results.  With the additional storm load last night, concern exists that this weak layer could fail.  A deep slab avalanche would have large consequences.   

    Deep slab avalanches are unpredictable and hard to collect additional information on.  Tracks on a slope will not be an indicator of stability.  Look for collapsing, cracking, or whumpfing sounds.  Although, no signs of instability may be present.  Remote triggering is possible, along with failure mid to low slope.  A storm snow related avalanche could have the potential to step down into these weak old snow layers.  Avoid steep avalanche terrain and runout zones where this problem may exist. 

Avalanche Discussion

* Wind slab avalanches reported on Wildflower Ridge (Donner Summit area) and Stevens Peak (Carson Peak area).

* Wind slab development with unstable test results on Red Lake Peak (Carson Pass area) and Rubicon Peak (West Shore area).

* Buried surface hoar has been observed on Andesite Peak and Wildflower Ridge (Donner Summit area), Silver Peak (Pole Creek area), Lincoln Ridge (Yuba Pass area), and Squaw Ridge (Carson Pass area).

* Snowpack tests targeting the deep persistent weak layer yesterday showed unstable results on Wildflower Ridge (Donner Summit area) and Stevens Peak (Carson Pass area).

Regions covered