THIS AVALANCHE ADVISORY EXPIRED ON December 31, 2016 @ 6:45 am
Avalanche Advisory published on December 30, 2016 @ 6:45 am
Issued by Steve Reynaud - Tahoe National Forest

Moderate avalanche danger continues to be possible throughout most of the forecast area due to persistent slabs.  These persistent slabs are found on slopes steeper than 32 degrees at all elevations mainly along the Sierra Crest.  Human triggered avalanches remain possible today. 

2. Moderate

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

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
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    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Persistent slabs continue to remain possible due to persistent weak layers found near the Dec. 15 rain crust.  In most areas, but not all, near crust facets are the primary persistent weak layer formed above the Dec. 15 rain crust and are now buried under the most recent storm snow.  There is variability as to where these persistent slabs exist, they have been found to be mostly along the Sierra Crest on W-NW-N-NE-E aspects at all elevations.  Where deeper snowpacks exist at higher elevations in the Mt. Rose area, this persistent slab avalanche problem has been found to be unlikely.  Recent snowpack tests along the Sierra Crest continue to show weakness around the Dec. 15 rain crust and that propagation is likely if this weak layer could be triggered.

Persistent slab avalanches are unpredictable and require different terrain management techniques.  These avalanches could be triggered low on a slope and away from what we think of as traditional ridgetop wind slab start zones.  Wide propagation is possible into connected terrain.  Use conservative decision making and travel techniques. 

recent observations

Observations were received yesterday from Red Lake Peak (Carson Pass area) and Polaris Point (Ward Canyon area).  Both locations showed snowpack tests failing near the Dec. 15 rain crust on persistent weak layers.  Snowpack tests continue to show that propagation is likely if these weak layers can be triggered.  A high level of variability exists even in one area as to where these weak layers exist and where they don't.  On Polaris Point, a shallow and variable snowpack existed below 7800'.  On Red Lake Peak, some evidence of recent warming related loose wet activity existed.  At both locations, wet and sticky surface snow was found on southerly aspects by mid day.

Weather and CURRENT CONDITIONS
weather summary

A weak cold front will bring increased winds with a chance of very light snow tonight and into Saturday morning.  SW wind gusts over ridgetops could reach up to 50mph this afternoon.  Up to 1 to 2 inches of snow is possible into Saturday.  A cold front drops down from the North starting Sunday evening with chances of measurable snow and well below average temperatures.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 30 to 40 deg. F.
Max. temperature in the last 24 hours: 53 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 10 to 25 mph
Maximum wind gust in the last 24 hours: 41 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: Along the Sierra Crest 25 to 38 inches | In the Mt. Rose area 56 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Partly cloudy. Partly cloudy then becoming mostly cloudy. Isolated snow showers after midnight. Mostly cloudy. Chance of snow showers.
Temperatures: 40 to 46 deg. F. 19 to 24 deg. F. 30 to 35 deg. F.
Wind Direction: SW SW NE
Wind Speed: 10 to 15mph with gusts to 40mph. 10 to 15mph with gusts to 35mph. Light winds becoming NE 10 to 15mph in the afternoon. Gusts up to 30mph.
Expected snowfall: 0 in. Trace in. Up to 1 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Partly cloudy. Partly cloudy then becoming mostly cloudy. Isolated snow showers after midnight. Mostly cloudy. Chance of snow showers.
Temperatures: 35 to 41 deg. F. 16 to 21 deg. F. 28 to 33 deg. F.
Wind Direction: SW SW E
Wind Speed: 20 to 30mph with gusts to 50mph. 15 to 25mph with gusts to 50mph. 15 to 20mph with gusts to 45mph.
Expected snowfall: 0 in. Trace in. Up to 1 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.

For a recorded version of the Avalanche Advisory call (530) 587-3558 x258