THIS AVALANCHE ADVISORY EXPIRED ON December 21, 2014 @ 6:51 am
Avalanche Advisory published on December 20, 2014 @ 6:51 am
Issued by Brandon Schwartz - Tahoe National Forest

Near and above treeline, avalanche danger remains MODERATE on NW-N-NE-E-SE aspects on slopes 35 degrees and steeper due to ongoing concern for human triggered wind slabs. For all other areas, avalanche danger is LOW.

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.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    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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    Certain
    Very Likely
    Likely
    Possible
    Unlikely
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    Historic
    Very Large
    Large
    Small

New wind slabs that formed during the past 24 hours are expected to remain unstable today. Human triggered wind slabs up to 2 feet deep are possible in areas along the Sierra Crest. Smaller wind slabs 6 to 18 inches deep are expected in other areas. Pick and choose wisely when dealing with wind loaded NW-N-NE-E-SE aspect slopes steeper than 35 degrees. Wind slabs are avoidable by studying the snow surface and identifying areas that are vs. areas that are not wind loaded. Evaluate consequences of getting caught in an avalanche in terms of potential impact with trees or deep burial in terrain traps. Travel one at a time in avalanche terrain, moving from one high quality island of safety to the next. These types of simple hazard recognition, informal information gathering, and deliberate informed decision making are a big part of the difference between "getting lucky" and "getting it done" in the backcountry.

recent observations

Observations made yesterday on Mt. Judah's Wildflower Ridge (Donner Summit area) revealed that easily human triggered wind slabs had formed in wind loaded areas by noon. Skier triggered wind slabs propagating up to 40' wide were noted on NE aspect test slopes at 7,800' with slab depth at that time of 4 to 10 inches. These wind slabs were failing on a weak layer of lower density storm snow at the base of the wind slab. No evidence of buried surface hoar was observed in wind protected locations in the area. Additional observations received from the Mount Rose area indicated smaller, significantly less sensitive wind slabs had formed in wind loaded areas along ridgelines. No evidence of buried surface hoar was noted in that area either.

Weather and CURRENT CONDITIONS
weather summary

New snow amounts from the past 24 hours of 5 to 10 inches exceeded upper end forecast amounts for areas above 7,000'. Snow showers will gradually taper off from south to north this afternoon and evening as the current storm system exits the area. Snow levels rose yesterday afternoon and evening up to 6,500' to 7,000'. Snow levels may fall a bit this morning before rising to near 7,000' again this afternoon. Remote sensors are reporting air temperatures this morning in the mid 20s to low 30s for stations at 8,000' to 9,000'. Maximum daytime air temperatures are forecast in the low to upper 30s today for areas above 7,000'. Ridgetop winds remain out of the southwest and are strong in speed. Strong southwest winds are forecast to continue today, increasing to gale force tonight. High pressure will build into the region on Sunday and last through the early part of the week.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 26 to 32 deg. F.
Max. temperature in the last 24 hours: 28 to 32 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 39 mph
Maximum wind gust in the last 24 hours: 70 mph
New snowfall in the last 24 hours: 5 to 10 inches
Total snow depth: 28 to 40 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy skies with a chance of snow. Mostly cloudy skies with a slight chance of snow. Mostly cloudy skies becoming partly cloudy.
Temperatures: 32 to 39 deg. F. 26 to 32 deg. F. 40 to 47 deg. F.
Wind Direction: SW SW W
Wind Speed: 10 to 20 mph with gusts to 30 mph. 15 to 25 mph with gusts to 40 mph. 15 to 25 mph with gusts to 40 mph.
Expected snowfall: Trace to 2 in. Trace to 1 in. 0 in.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy skies with a chance of snow. Mostly cloudy skies with a slight chance of snow. Mostly cloudy skies becoming partly cloudy.
Temperatures: 29 to 35 deg. F. 26 to 33 deg. F. 33 to 40 deg. F.
Wind Direction: SW W W
Wind Speed: 30 to 40 mph with gusts to 60 mph. 50 to 60 mph with gust to 80 mph. 50 to 55 mph with gusts to 85 mph, decreasing to 40 to 45 mph with gusts to 65 mph in the afternoon.
Expected snowfall: Trace to 2 in. Trace to 1 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.