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

MODERATE avalanche danger exists on NW-N-NE-E-SE aspects steeper than 35 degrees in near and above treeline terrain due to new wind slabs. Some isolated pockets of MODERATE danger may exist on NW-N-NE aspects steeper than 35 degrees at all elevations north of Emerald Bay due to storm slabs forming above a lingering persistent weak layer. Evaluate the snow and terrain carefully before committing to a slope instead of letting the excitement of early season snow lead to poor decision making.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Last night's new snow and wind caused new wind slabs to form on the leeward slopes in near and above terrain. These wind slabs will exist in any open areas where wind loading occurred. Human triggered avalanches involving these wind slabs will be possible today. The largest and most sensitive of these wind slabs will exist on wind loaded N-NE-E aspects and cross loaded NW and SE aspects in the northern half of the forecast area where more new snow fell. Smaller wind slabs will exist in the southern half of the forecast area where less snow fell. Avalanches involving these wind slabs could involve enough snow to bury a person especially in the most heavily wind loaded areas or where they occur in combination with a terrain trap. Blowing snow, cornices above slopes, wind pillows, and other wind created features can help identify where wind slabs may exist.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1

    Some isolated and small storm slabs may exist on NW-N-NE aspects along the Sierra Crest north of Emerald Bay where more snow fell. These storm slabs should remain confined to the isolated areas where the new snow accumulated on top of a snowpack where buried facet layers have remained reactive. Data has shown that even though most of these layers should handle the additional weight of 8 to 12 inches new snow well, a few isolated areas may not. Due to the variability associated with the buried weak layer, some uncertainty exists about which slopes or even which parts of the same slope will be ok and which ones may remain sensitive. In addition to the isolated nature of this problem the numerous anchors that disrupt the weak layer should keep any instabilities confined to smaller areas. This problem may transition to a persistent slab problem in the coming days or not depending on how the buried weak layers adjust to the new load.

Avalanche Discussion

Recent observations from around the forecast area have shown a warming snowpack with snow surfaces varying from melt-freeze crusts to wind scoured surfaces. Snowpit tests and other data have mostly indicated that this snowpack has consolidated and gained strength in most areas. Some data still indicates that the weak layers buried on some of the northerly aspects remain weak. Observations on northerly aspects between 7800 and 8800 ft. on Castle Peak yesterday highlighted this variability. Most of the snowpit data and tests did not reveal any signs of lingering instbaility; however, one of the locations tested on a NW aspect at 8800 ft. did indicate that if the facets at the bottom of the snowpack do break, the resulting fracture could travel along that weak layer.

Regions covered