Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
View on map

Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
Open full map
Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Continued gale force winds with additional snowfall will make wind slab avalanches likely in near and above treeline areas.  Deep persistent slab avalanches will remain possible with the potential for large avalanches failing on weak layers deep within the snowpack.  CONSIDERABLE avalanche danger will continue 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

    SW winds have been elevated for multiple days and will continue to be gale force in speed through today.  New snowfall from yesterday along with additional snowfall today will allow for available snow for wind transport and new wind slab development.  Wind slab avalanches will be likely on NW-N-NE-E-SE aspects in near and above treeline terrain.

    Look for blowing snow, cornice formation, and wind pillows as indications on where wind slabs are forming.  Areas below cornices and wind pillows will be most suspect for wind slab avalanches.  Make a plan to move around these areas of concern while traveling in the backcountry.  

  • Deep Persistent Slabs

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

    Human triggered deep persistent slab avalanches remain possible on NW-N-NE aspects at all elevations.  These avalanches could fail on deeply buried weak layers within the snowpack causing large and destructive avalanches.  The last reported avalanche associated with this problem was triggered on Sunday afternoon on Waterhouse Peak in the Luther Pass area. 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.

    Deep slabs are very unpredictable and difficult to collect additional information about, there may be limited or no signs of instabilities until a large avalanche occurs.  Areas that had a shallow and weak snowpack structure before the last major storm are most suspect for this deep slab avalanche problem to occur.  Until this avalanche problem goes away, good terrain management skills are critical to reduce exposure.  Utilize terrain under 30 degrees in steepness and areas away from steeper connected terrain.  Avoid complex terrain with multiple trigger points and unsupported slopes.   

    Bed surface from deep persistent slab avalanche triggered on Sunday Jan 31 on Waterhouse Peak, Luther Pass area.

Avalanche Discussion

*  Observations from Silver Peak, (Pole Creek area), had up to 5'' of high density storm snow by early afternoon.  Strong to gale force SW winds were blowing snow and building out cornices and wind slabs. 

*  Snowpack test results submitted from Waterhouse Peak, (Luther Pass area), continued to show unstable test results on weak layers buried deep in the snowpack.     

*  A deep persistent slab avalanche that occurred on Waterhouse Peak (Luther Pass area) on Sunday afternoon Jan 31 was investigated.  Report here.

* 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 avalanches continue to be reported. 

Regions covered