Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

The avalanche danger remains MODERATE due to old and new wind slabs in near and above treeline terrain. Some loose wet avalanches may become possible as the day warms up.  Unlikely but not impossible persistent slabs may also linger in below treeline areas, especially in the Carson Pass region. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    The E and NE winds yesterday afternoon and evening may have grown strong enough to form small wind slabs near ridgelines on some S-SW-W aspects. In addition to these new wind slabs, older, larger, and still potentially unstable wind slabs could linger on near and above treeline N-NE-E aspects loaded by previous SW winds. Wind slabs could also exist on NW and SE aspects where either wind direction could cross-load the slope. Avalanches resulting from the failure of these wind slabs could involve enough snow to bury or injure a person (size D2).

    Human triggered wind slabs avalanches are still possible today. Use clues like wind drifted snow, cornices above slopes, wind pillows, and wind-sculpted snow surfaces to identify and avoid areas of potentially unstable wind slabs.

     

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Today's warm sunny weather could cause enough warming and melting for loose wet avalanches to become possible on steep sun-exposed SE-S-SW aspects. This loose wet avalanche problem could take the form of roller balls, pinwheels, or point release avalanches. Most of these should not entrain enough snow to bury a person, but they could knock a person over or push a person into terrain where collisions or a fall would have serious consequences. 

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    Snowpit tests and a recent avalanche with persistent slab characteristics indicates that a persistent slab problem may still linger on some NW-N-NE facing slopes in the Carson Pass area. A layer of loose weak snow near a crust 8 to 12 inches below the surface represents the persistent weak layer for this problem. Observations from Crater Lake, Meiss Meadows, Elephants Hump, and Squaw Ridge prior to last week's storms showed the existence of this weak layer. Uncertainty still remains as to whether or not this weak layer remains widespread or how it has reacted to the new snow due to a limited amount of data targetting this layer. If this problem does exist it will linger in near and below treeline areas on NW-N-NE aspects and mainly be focused in the Carson Pass area. Persistent slab avalanches could involve enough snow to bury or injure a person if they do occur (size D2 with some potential for an isolated D3).

    Look for and avoid avalanche terrain in any areas where snow surface cracking, snowpack collapse with a possible whumpfing sound, and/or unstable snowpit test results are occurring.

    Concern for this avalanche problem continues to decrease on a regional scale as the deeply buried facet layer from December and the now unreactive buried surface hoar are no longer the main focus of this avalanche problem. Concern remains elevated for the Carson Pass area and for any yet to be observed areas where this same near crust facet layer exists.

Avalanche Discussion

* A skier triggered avalanche about 60 ft. wide and 1 ft. deep was reported on the N side of Castle Peak on a NE facing above treeline slope in typically wind loaded terrain yesterday. It broke around the skier who triggered it and carried the skier about 150 ft. downslope but did not bury the skier. Other wind slab avalanches were reported on Friday in the Bronco Chutes of Relay Peak (Mount Rose area), Thursday from the Far East Ridge of Tamarack Peak (Mount Rose area), and from the south end of Andesite Ridge (Donner Summit area). 

* Ski cuts on recently wind-loaded slopes along Chickadee Ridge (Mount Rose backcountry) and snowmobile cuts on wind-loaded test slopes near Blue Lakes (Carson Pass area) both produced shooting cracks yesterday indicating lingering wind slab instability. 

* Warming surface snow was reported on sun-exposed slopes of Carpenter Peak (near Independence Lake) and some roller balls started to occur near rocks on SE facing slopes near Blue Lakes (Carson Pass area) yesterday afternoon.

* Snowmobilers reported a recent avalanche on the Nipple (in the Blue Lakes area) that likely failed on the persistent weak layer of facets near a crust and was likely triggered by a nearby loose dry sluff. Snowpit tests targetting that persistent weak layer of facets buried about 8 to 12 inches below the surface near a crust still produced unstable results on N aspects near Lost Lakes (Carson Pass area) yesterday. A skier on Waterhouse Peak (Luther Pass area) also reported a facet layer at a similar depth.

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