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

Unstable conditions are expected to continue today with a slower than typical post-storm stabilization process. Both persistent slab and wind slab avalanches occurred yesterday and could be triggered again today. Conservative, sub 30 degree slope angle terrain choices are highly recommended for today. Today is not the day to go big. Avalanche danger remains CONSIDERABLE for all elevations.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    This avalanche problem is becoming increasingly scary as the problematic weak layers of old faceted (sugary) snow (Dec 11 PWL and Dec 17 weak layer) are buried deeper in the snowpack. The weak layer(s) associated with this avalanche problem have reactivated under the new snow load. One of yesterday's avalanche incidents appears to have been a persistent slab avalanche. This avalanche problem exists on W-NW-N-NE-E aspects, has a widespread distribution in below treeline and near treeline terrain, and isolated distribution above treeline.

    Whumpfing, shooting cracks, recent avalanches, and unstable snowpit test results are all indications of unstable snow in the area. Do not write off the significance of any of these clues when dealing with a persistent slab avalanche problem, even if they seem isolated. If you choose not to scale back route choices to less than 30 degree angle slopes only, this is a difficult avalanche problem to manage. Signs of instability may or may not readily present themselves prior to triggering an avalanche. Do not underestimate potential avalanche size, potential runout distance, or the hazard from connected terrain above or to the side. It would be fairly easy to encounter a persistent slab avalanche today while trying to avoid wind slabs. Route find to avoid both.

      Weak layer unverified but the jagged crown suggests a persistent slab avalanche. Skier triggered on the ascent from the red X location on Nipple Pk.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Large amounts of wind drifted snow continue today as problematic wind slabs. The second of yesterday's avalanche incidents was a wind slab that failed under 6 feet of wind drifted snow. This avalanche failed at the old/new snow interface which has the potential for slower than typical stabilization today. This avalanche problem exists on NW-N-NE-E-SE aspects in above treeline and near treeline terrain.

    Slopes near ridgetops in the immediate vicinity of cornices and pillows of wind drifted snow are highly suspect. These wind slabs will seem stiff and dense and will likely be difficult to trigger from the edges, potentially not failing until a person is fully out on the slab. Last night's shift to E winds may have scoured these wind slabs slightly, but they are still plenty thick. Identify specific areas of concern and move around them with caution and an avoidance mindset. It would be fairly easy to encounter a wind slab avalanche today while trying to avoid persistent slabs. Route find to avoid both.

         Yesterday's deep wind slab avalanche in the Little Truckee Summit/Independence Lake zone.

Avalanche Discussion

* Two people were caught in avalanches yesterday, nearly or fully buried without injury. SAC is grateful that no one was injured and greatly appreciates receiving the submitted information to inform this product.

* One avalanche incident was a deep wind slab failing on the old/new snow interface on a NE aspect at around 7,800' in near to above treeline terrain. This was snowmobile triggered in the Little Truckee Summit/Independence Lake zone. Crown depth was around 6 feet.

* The second avalanche incident appears to have been a persistent slab likely failing on the Dec 11 PWL on a NE aspect at around 8,400' in above treeline terrain. This was skier triggered on an ascent of Nipple Peak, south of Carson Pass. Much less is known about this avalanche.

* Yesterday's snowpit data from a variety of locations indicated unstable, problematic results on both the old/new snow interface and deeper in the snowpack on the Dec 11 persistent weak layer.

* Whumpfing was widespread yesterday and reported from numerous locations.

* Long shooting cracks were reported from several areas.

Regions covered