THIS AVALANCHE ADVISORY EXPIRED ON November 27, 2015 @ 6:51 am
Avalanche Advisory published on November 26, 2015 @ 6:51 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE avalanche danger exists on all aspects and elevations on slopes 35 degrees and steeper. Wind slabs represent the primary avalanche concern on near and above treeline slopes with loose dry sluffs posing more of an issue in sheltered terrain. Human triggered avalanches remain possible today. 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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While many of the wind slabs that formed during the storm have become slightly more difficult to trigger, human triggering of these slabs remains possible. Stepping on or riding over trigger points or having more than one person on a slope would make triggering these wind slabs easier. In addition to the wind slabs that formed on the N-NE-E aspects during the storm, new wind slabs may have started to form on the opposite aspects (W-SW-S) since the winds have shifted to the north and east. These new wind slabs will remain smaller, but more sensitive than the older ones. The NW and SE aspects get cross loaded with both wind directions. Wind slabs could exist on any exposed near and above treeline aspects today. Most avalanches that result from the failure of these wind slabs should fail at or above the old snow surface; however, some of them could step down into older snow layers in areas where the wind slabs exist on top of old hard slabs on the NW-N-NE aspects. Avalanches involving wind slabs could entrain enough snow to bury a person.

Cornices above a slope, wind ripples, drifts, blowing snow, and other signs of wind loading can all serve as clues to help recognize slopes where wind slabs may exist. If a near or above treeline area looks nicely filled in and smooth and rounded, wind slabs likely exist in that area. Complex or extreme terrain like couliors and unsupported slopes will hold unstable wind slabs longer than other terrain and also have more potential consequences.

Avalanche Problem 2: Loose Dry
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Loose dry snow sluffs will remain possible today. Steep slopes in near and below treeline terrain on NW-N-NE-E aspects sheltered from the winds hold the best potential for these kind of instabilities since they had more previous snow coverage. These instabilities could also exist on other near and below treeline aspects, but they will be more isolated and smaller on the SE-S-SW-W aspects due to the fact that most of those aspects did not have snow cover prior to this storm.

recent observations

Yesterday on Wildflower Ridge and Mt. Judah, ski cuts on steep non wind affected test slopes triggered loose dry sluffs, and ski cuts and kicks on some wind loaded test slopes triggered wind slab failures. These wind slabs had become slightly more difficult to trigger than the previous day. Additional weighting of the wind loaded test slopes where the new wind slabs rested on top of old hard slabs on top of old facets caused failures in the facets below the old hard slabs. Snowpit data also indicated that areas with this layering remain suspect and that failures could occur in the old snow layers in these places. Stepping into the snow to dig a snowpit in one of these locations also triggered a large whumph as the lower weak layer collapsed.

Weather and CURRENT CONDITIONS
weather summary

After another round of light accumulation yesterday morning, snow showers tapered off during the day. These snow showers added another 2 to 5 inches of snow to the storm totals. Areas east of Lake Tahoe received the higher precipitation amounts. The winds shifted to the north and east yesterday afternoon and started increase some during the night. The cold low pressure system remains stalled over the Great Basin and will keep temperatures cold and winds out of the north and east. Some small show showers may also develop during the next few days, but the forecast calls for little to no additional accumulation. Daytime highs will remain in the teens and overnight lows could dip into the single digits above 7000 ft.  

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 10 to 15 deg. F.
Max. temperature in the last 24 hours: 17 to 24 deg. F.
Average wind direction during the last 24 hours: Southwest shifting to northeast around noon yesterday
Average wind speed during the last 24 hours: 5 to 20 mph
Maximum wind gust in the last 24 hours: 34 mph
New snowfall in the last 24 hours: 2 to 5 inches
Total snow depth: 15 to 25 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy with isolated snow showers Mostly cloudy with scattered snow showers Mostly cloudy with a 30% chance of snow showers in the afternoon
Temperatures: 14 to 21 deg. F. 3 to 10 deg. F. 14 to 21 deg. F.
Wind Direction: Northeast East Northeast
Wind Speed: 10 to 15 mph 15 to 20 mph with gusts to 30 mph 15 to 20 mph with gusts to 30 mph
Expected snowfall: trace to 0 in. trace to 0 in. trace to 0 in.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy with isolated snow showers Mostly cloudy with scattered snow showers Mostly cloudy with a 30% chance of snow showers in the afternoon
Temperatures: 11 to 18 deg. F. 3 to 10 deg. F. 10 to 17 deg. F.
Wind Direction: Northeast East East
Wind Speed: 10 to 15 mph with gusts to 25 mph in the afternoon 15 to 25 mph with gusts to 35 mph 15 to 25 mph with gusts to 35 mph
Expected snowfall: trace to 0 in. trace to 0 in. trace to 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.