THIS AVALANCHE ADVISORY EXPIRED ON January 7, 2017 @ 6:54 am
Avalanche Advisory published on January 6, 2017 @ 6:54 am
Issued by Steve Reynaud - Tahoe National Forest

Moderate avalanche danger exists throughout the forecast area due to deep slab and wind slab avalanches.  Dangerous avalanche conditions continue to be possible with many deep slab avalanches occurring throughout the forecast area within the last 48 hours including a skier triggered deep slab avalanche in the Mt. Rose area yesterday partially burying a skier and a car.  Large avalanches with severe consequences could be human triggered today.   Cautious route finding and conservative decision making are essential.

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: Deep Slab
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Many large and destructive deep slab avalanches have occurred in the last 48 hours.  The recent storm snow is settling and consolidating quickly with the weak and developed facets above the Dec. 15 rain crust adjusting to this large new load.  A skier triggered deep slab avalanche yesterday, snowpack tests, informal observations, whumpfing sounds and widespread cracking all indicate that this layer is still reactive.  Large, destructive, human triggered deep slab avalanches remain possible today throughout the entire forecast area on W-NW-N-NE-E aspects at all elevations.  These slabs could measure anywhere from 4 to 10+ feet deep.

Deep slabs are unpredictable.  Remote triggering with large propagation into any connected terrain remains possible.  Large to historic runout zones could occur if a deep slab avalanche was triggered.  Ski tracks on a slope will not be an indicator of stability and steep trees will not be a safe zone.  Avalanche avoidance and cautious route finding remain the best practice to deal with this deep slab avalanche problem.

Avalanche Problem 2: Wind Slab
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Wind slabs will continue to be a problem on NW-N-NE-E-SE and in some areas S aspects in near treeline and above treeline terrain.  Winds shifted briefly overnight to the NE and were strong in speed for several hours at the highest elevations.  Any wind slab development that occurred from these NE winds is expected to be small and limited to the highest ridgetops and peaks.  Winds have shifted back to the SW and will be light throughout the day.  Recently formed wind slabs will need time to adjust and gain strength.

Look for cornice formation, snow surface scouring, and wind pillows to help identify areas where wind slabs have formed.  Use caution in these areas to avoid wind loaded terrain.

recent observations

Observations were made and received from Jakes Peak (West Shore area), Silver Peak (Pole Creek area), and Fireplug (Mt. Rose area).  Yesterday on Fireplug, a skier triggered deep slab avalanche partially buried a skier and an automobile on the highway.  Minor injuries were reported but the party of 2 was able to self evacuate from the scene.  This avalanche was triggered mid slope and propagated away from the skier with crown lines up to 6 feet deep.  Deep slabs, wind slabs, and storm slabs were observed on Jakes Peak and Silver Peak.  Snowpack tests and informal observations showed that triggering a deep slab avalanche continues to be possible.  Deep slabs on Jakes and Silver Peaks were mid slope below treeline terrain around 35 degrees in steepness. 

Limited information has come in of a natural avalanche on Polaris Bowl in the Carson Pass area.  Crown was thought to be 5 to 6 feet deep, released mid slope, with a long runout.  This avalanche has very similar characteristics and thought to also be a deep slab avalanche. 

The deep slab avalanche problem has been observed throughout the entire forecast area and continues to be an ongoing issue. 

Weather and CURRENT CONDITIONS
weather summary

Cold and quiet weather expected today with light winds.  A strong atmospheric river will impact the area from Saturday through Monday.  6 to 12 inches of liquid water is forecasted along the Sierra Crest with snow levels up to 9000-9500'.  Rainfall rates could approach .50 inches/hour during Sunday and Sunday night.  A flood watch is posted throughout the Sierra Nevada Mountains with flood impacts expected.   

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 8 to 23 deg. F.
Max. temperature in the last 24 hours: 28 deg. F.
Average wind direction during the last 24 hours: NE shifing to SW
Average wind speed during the last 24 hours: 10 to 15 mph
Maximum wind gust in the last 24 hours: 62 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: Along the Sierra Crest 60 to 73 inches | In the Mt. Rose area 98 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Sunny then becoming partly cloudy. Cloudy. Chance of snow after midnight. Cloudy. Snow through the morning. Rain in the afternoon.
Temperatures: 28 to 33 deg. F. 19 to 24 deg. F. 35 to 40 deg. F.
Wind Direction: S S
Wind Speed: Light winds. 10 to 15mph after midnight. Gusts to 30mph. 15 to 25mph with gusts to 45mph.
Expected snowfall: 0 in. 0 in. 5 to 10 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Sunny then becoming partly cloudy. Cloudy. Slight chance of snow after midnight. Cloudy. Snow
Temperatures: 27 to 32 deg. F. 19 to 24 deg. F. 33 to 38 deg. F.
Wind Direction: SW SW SW
Wind Speed: 10 to 15mph with gusts to 40mph in the afternoon. 20 to 30mph. Gusts to 50mph increasing to 65mph after midnight. 25 to 40mph with gusts to 90mph increasing to 40 to 60mph with gusts to 100mph in the afternoon.
Expected snowfall: 0 in. 0 in. 6 to 12 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