THIS AVALANCHE ADVISORY EXPIRED ON December 23, 2013 @ 6:43 am
Avalanche Advisory published on December 22, 2013 @ 6:43 am
Issued by Brandon Schwartz - Tahoe National Forest

Near treeline and below treeline, MODERATE avalanche danger continues on NW-N-NE aspects on slopes 32 degrees and steeper due to lingering persistent slabs.

Human triggered avalanches remain possible. Shallow covered rocks, logs, and stumps are an additional hazard to backcountry travelers. Impact with rocks or trees while caught in an avalanche can greatly increase consequences.

1. Low

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Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

2. Moderate

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Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Persistent Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Just over two weeks have past since the most recent significant snowfall event and persistent slab instability continues. While some small and very gradual improvement in stability has occurred over that time, it does not negate the fact that human triggered avalanches remain possible. The problematic faceted Dec 7 persistent weak layer remains widespread on NE wind protected slopes near treeline and below treeline on NW-N-NE aspects. Evidence of instability is still encountered on a near daily basis by backcountry travelers. Snowpit data continues to point out the current instability. Avalanche avoidance through travel on sub 32 degree slopes without steeper slopes above remains the best way to mitigate the hazard.

recent observations

Observations made yesterday near Grouse Rocks (Ward Canyon area) pointed towards two rather interesting conclusions regarding the persistent slab instability that exists near treeline and below treeline on NW-N-NE aspects. No obvious signs of instability were observed while on tour in the area and snowpit data revealed increased difficulty in triggering collapse and subsequent propagation along the faceted Dec 7 persistent weak layer. This indicates that some improvement in stability has occurred in this area. Despite the stability improvement, snowpit data also showed that two different N aspect below treeline slopes with ski tracks on them still had the ability to collapse and propagate along the Dec 7 persistent weak layer. This indicates that if the right trigger point is found on the slope, the necessary snowpack ingredients for a human triggered avalanche remain present.

Rocks, logs, and stumps lurk below the snow surface. The ability of the snowpack to keep a person supported above these hazards remains variable and can change greatly over short distances. Travel accordingly to minimize the risk of injury.

Weather and CURRENT CONDITIONS
weather summary

High pressure is firmly in place over the forecast area. Weather systems passing by to the north of the region have allowed for a bit of low level and high level cloud cover to move into the forecast area. This cloud cover is expected to clear the region as the day progresses leading to sunny skies. Ridgetop winds remain out of the northeast this morning and are moderate in speed. Winds are forecast to become light through the afternoon and overnight hours. West winds are forecast for Monday. For the next couple of days, periodic cloud cover leading to partly cloudy skies is expected over the region as additional weather systems pass by to the north.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 27 to 32 deg. F.
Max. temperature in the last 24 hours: 31 to 40 deg. F.
Average wind direction during the last 24 hours: NE
Average wind speed during the last 24 hours: 26 mph
Maximum wind gust in the last 24 hours: 48 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 10 to 19 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy skies, becoming sunny. Clear skies. Sunny skies.
Temperatures: 37 to 44 deg. F. 23 to 31 deg. F. 42 to 49 deg. F.
Wind Direction: NE E Variable
Wind Speed: 20 to 25 mph with gusts to 35 mph, decreasing to 10 to 15 mph with gusts to 25 mph in the afternoon. 10 to 15 mph. Light winds.
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy skies, becoming sunny. Clear skies. Sunny skies.
Temperatures: 35 to 42 deg. F. 23 to 30 deg. F. 40 to 47 deg. F.
Wind Direction: NE NE W
Wind Speed: 20 to 30 mph with gusts to 40 mph. 15 to 20 mph with gusts to 30 mph. 10 to 15 mph. Gusts to 25 mph in the afternoon.
Expected snowfall: 0 in. 0 in. 0 in.
Disclaimer

This avalanche advisory is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This advisory covers the Central Sierra Nevada Mountains between Yuba Pass on the north and Ebbetts Pass on the south. Click here for a map of the forecast area. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.