THIS AVALANCHE ADVISORY EXPIRED ON December 5, 2015 @ 7:00 am
Avalanche Advisory published on December 4, 2015 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest

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.

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: Wind Slab
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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.

Avalanche Problem 2: Storm Slab
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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.

recent observations

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.

Weather and CURRENT CONDITIONS
weather summary

8 to 12 inches of new snow has accumulated along the Sierra Crest north of Emerald Bay since yesterday afternoon. South of Emerald Bay remote sensors report 3 to 5 inches of new snow along the crest. East of the lake sensors showed a similar pattern with about 7 inches of new snow reported in the Mt. Rose area and 3 to 4 inches on the southeast side of the lake. Most of this snow fell between 4 pm and 10 pm last night. The winds during this storm averaged between 40 and 50 mph from the southwest with gusts as high as 93 mph. Snow showers should continue to dissipate, and the winds and cloud cover should continue to decrease as a high pressure ridge moves over the area today. This ridge will bring cold, dry, and mostly clear weather to the region for this afternoon and tonight before the winds and cloud cover start increasing ahead of a small low pressure system tomorrow. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 20 to 26 deg. F.
Max. temperature in the last 24 hours: 34 to 44 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 45 mph
Maximum wind gust in the last 24 hours: 93 mph
New snowfall in the last 24 hours: North of Emerald Bay: 8 to 12 inches | South of Emerald Bay: 3 to 5 inches
Total snow depth: 18 to 26 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy with a chance of scattered snow showers in the morning. Clouds decreasing during the day. Partly cloudy becoming clear overnight Mostly cloudy
Temperatures: 28 to 33 deg. F. 16 to 21 deg. F. 35 to 42 deg. F.
Wind Direction: Southwest Variable South
Wind Speed: 10 to 20 mph with gusts between 25 and 30 mph Light Light in the morning increasing to 10 to 20 mph with gusts between 25 and 30 mph in the afternoon
Expected snowfall: up to 1 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy with a chance of scattered snow showers in the morning. Clouds decreasing during the day. Partly cloudy becoming clear overnight Mostly cloudy
Temperatures: 22 to 28 deg. F. 18 to 22 deg. F. 34 to 41 deg. F.
Wind Direction: Southwest shifting to west West Southwest shifting to south
Wind Speed: 25 to 35 mph with gusts to 50 mph decreasing to 15 to 25 mph with gusts to 35 mph in the afternoon 10 to 15 mph with gusts to 25 mph decreasing after midnight 10 to 15 mph increasing to 30 to 40 mph with gusts to 60 mph in the afternon
Expected snowfall: up to 1 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.