Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
4 · High
Treeline
4 · High
Below
4 · High
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Highlights

HIGH avalanche danger exists at all elevations. Widespread, large destructive natural avalanche activity is likely and human-triggered avalanches are very likely. Very dangerous and complex avalanche conditions continue due to a mix of wind slabs, storm slabs, and deep persistent slabs. Travel in, below, or near avalanche terrain is not recommended.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2

    Fragile wind slabs have formed on wind-loaded slopes. Wind slabs could exist at any elevation including in some below treeline areas. The largest wind slabs should reside in near and above treeline terrain on NW-N-NE-E-SE aspects. Large and destructive wind slab avalanches are very likely today. Remote triggering is possible, avalanches could propagate wider than normal or even across connected slopes, and wind slab avalanches could run farther downslope than expected especially in areas where the wind slabs may rest on buried surface hoar. Wind slabs will continue to become larger and more widespread during this storm. 

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2

    Large storm slab avalanches are also very likely today. Rapid loading from 2-3 in/hr snowfall rates could easily cause a failure in the storm snow weaknesses, the upside-down layering, and/or the buried surface hoar layer at the base of the storm snow. Storm slab avalanches could occur on any slopes steep enough to avalanche including in areas typically thought of as safe like tree-covered slopes or lower elevation slopes. Storm slabs could fracture wider and deeper than expected and be remotely triggered. Like the wind slabs mentioned above, they will become more widespread and larger as more snow accumulates. 

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    3

    Deep slab avalanches could occur today as well due to the additional weight of several feet of new snow overloading the old persistent weak layers buried several feet below the surface. Smaller triggers in the right places like a person on a trigger point or larger triggers like the weight of the new snow, cornice collapses, or other avalanches could cause a deep slab to release. If a deep slab avalanche does occur, it would be large, destructive, and unsurvivable. More snow today will make deep slab avalanches more likely.

Avalanche Discussion

* Observers reported numerous natural avalanches capable of burying a person or even a car on Incline Lake Peak, Tamarack Peak, and along Hwy 89 north of Tahoe City. 

* Remotely triggered avalanches big enough to bury a person or car were reported from Elephant's Hump and Slide Mountain. Another group remotely triggered a test slope north of Basin Peak. The people who triggered these were between 10 and 100 ft away from the avalanches. 

* Many of these avalanches likely failed on buried surface hoar.

* Observers on Luther Pass, in Ward Canyon, in the Mt. Rose backcountry, on the West Shore, on Brockway Summit, in areas north of Donner Summit, and in the Carson Pass backcountry all experienced shooting cracks, found an upside-down snowpack, and saw active wind loading. Most also had test slope failures in wind slabs and storm slabs and found buried surface hoar along with unstable snowpit test results on the surface hoar and other storm snow layers. 

Regions covered