Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Human triggered avalanches remain possible today.  Large slabs of wind drifted snow remain in exposed areas along with potentially unstable snow in sheltered areas.  Look for signs of instability like recent avalanches, blowing snow, and cracking in the snowpack.  Utilize non avalanche terrain if signs of unstable snow exist.

Avalanche problems

  • Wind Slabs

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

    Large wind slabs exist on NW-N-NE-E-SE aspects in near treeline and above treeline terrain.  Multiple wind slab avalanches have been reported over the last couple days throughout the forecast region.  Strong to gale force South winds today will continue to build these existing wind slabs and may form new wind slabs on slightly different aspects and locations due to the change in wind direction.  Existing wind slabs will be dense and could be stubborn to trigger.  Large cornices exist along most exposed ridges and could still be fragile.

    Recent avalanches, blowing snow, wind pillows, and snow surface clues will all indicate the presence of wind slabs.   Make a plan to avoid steep wind loaded slopes with large cornices above.  Better snow quality will exist in wind protected below treeline areas today.

    (1/11/2023)

    Large natural wind slab avalanche on the East Ridge of Tamarack Peak, Mt. Rose area.

    Photo: Steve Reynaud

  • Persistent Slabs

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

    The last few weeks have brought constant storms and fluctuating snow levels to our forecast region.  Several of these storms have added rain crusts to our existing snowpack with weak faceted snow potentially developing around them.  Snowpit tests on NW-N-NE aspects between 7,500 ft and 8,500 ft in the Border Ruffian and Blue Lakes areas south of Carson Pass have produced unstable results on the Jan 4 rain crust.  There has potentially been 1 large avalanche associated with one of these buried rain crusts 4 days ago at Blue Lakes, in the Carson Pass area.  Observations at various elevations in the Independence Lake, Donner Summit, Pole Creek, Mount Rose, and West Shore Tahoe zones have not found evidence of faceting or weakness on this layer. Substantial unknowns remain regarding the areas where these layers are weak and problematic.  These weak layers would be buried in the snowpack over 3 to 5 feet deep.

    An avalanche that fails on any of these crust/facet layers, would fail multiple feet deep in the snowpack, likely have wide propagation, and could be triggered from low on a slope or the side.  If any questions exist about whether or not these layers are present or remains unstable in the area, pull back into  sub 30 degree terrain with no overhead hazard.

    (1/8/2023)

    Natural avalanche in Polaris Bowl on The Nipple, south of Carson Pass, CA. This avalanche occurred during a period of intense wind loading. Unconfirmed, but based on the wide propagation and areas of jagged crown, this may have been a persistent slab avalanche failing on the Jan 4 crust/facet layer.

    Photo: Public

Avalanche Discussion

  • Large wind slab avalanches were reported over the last couple days on NE-E aspects in near and above treeline terrain.  Storm slab avalanches were also reported on steep slopes in near and below treeline terrain on Tuesday and Wednesday. They ranged in size, but some involved more than enough snow to bury or injure a person.
  • A very large avalanche (D2.5) that may have failed on the facets around the Jan 4 rain crust occurred naturally on 1/8 during intense wind loading in Polaris Bowl on The Nipple, south of Carson Pass.

Regions covered