THIS AVALANCHE FORECAST EXPIRED ON December 6, 2017 @ 6:49 am
Avalanche Forecast published on December 5, 2017 @ 6:49 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

MODERATE avalanche danger will continue to exist in near and above treeline terrain due to new wind slabs created by the strong NE winds and older wind slabs leftover from the recent storm. Human triggered avalanches remain possible. Identify where wind slabs exist and avoid steep wind-loaded terrain. Firm, scoured, or icy surfaces could also exist on exposed near and above treeline terrain.

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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E and NE winds have varied greatly by location since they started on Sunday night. In some areas, they have likely scoured previously wind-loaded N-NE-E aspects and redeposited the previous wind slabs onto the opposite aspects. Expect to find new wind slabs on W-SW-S aspects and on cross-loaded NW and SE aspects. These new wind slabs should remain limited to specific areas in near and above treeline terrain near ridgelines where the strongest NE winds have occurred. In areas where weaker NE winds occurred, some of the wind slabs that formed during the storm on the near and above treeline NW-N-NE-E-SE aspects may still linger. The possibility remains for the additional weight of a person on wind-loaded slopes to trigger new or old wind slabs today in some areas. 

Use clues like blowing snow, cornices above slopes, drifted snow, ripples in the snow surface, and other wind created textures to identify where wind slabs may exist and avoid those areas. Travelling in sheltered non-wind-affected terrain should provide safer and more enjoyable conditions today. 

recent observations
Submit Observations

* Some continued skier triggered cracking on wind-loaded test slopes on Rubicon Peak.

* Widespread surface hoar on Rubicon Peak.

* Reports of E wind scouring in the Tamarack Peak area. Firm, icy, scoured surfaces may exist on any terrain exposed to the strong NE winds across the forecast area.

* Some evidence of reactive wind slabs on Donner Summit on Sunday in the form of skier triggered cracking and ECTP results.

Snow coverage is deepest in areas above 8000 ft. in the northern half of the forecast area (north of Emerald Bay). Even at these elevations, snow coverage varies by location. Some areas at the upper elevations south of Emerald Bay still have marginal snow coverage. Below 8000 ft. most areas still have patchy snow coverage with many exposed obstacles and areas of bare ground. 

Weather and CURRENT CONDITIONS
weather summary

Strong E and NE winds continued overnight. These winds averaged in the 35 to 50 mph range with gusts to 60-80 mph in most locations along the highest ridgetops. One sensor at Ward Peak did record gusts as high as 114 mph. These winds should remain strong this morning, but they should begin to decrease during the day as the high-pressure ridge settles in place over the forecast area. This high-pressure will bring clear dry weather to the region for the foreseeable future. Over the next 2 days, temperatures at upper elevations should begin to warm up some, but as the wind dies down cold air may remain trapped in the valleys creating inversion conditions. 

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 19 to 26 deg. F.
Max. temperature: 20 to 28 deg. F.
Average ridgetop wind direction: Northeast
Average ridgetop wind speed: 35 to 50 mph
Maximum ridgetop wind gust: 114 mph
New snowfall: 0 inches
Total snow depth: 15 to 34 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny Clear Sunny
Temperatures: 33 to 38 deg. F. 11 to 16 deg. F. 38 to 43 deg. F.
Mid Slope Winds: East Variable Variable
Wind Speed: 10 to 15 mph with gusts to 45 mph decreasing to 35 mph in the afternoon Light Light
Expected snowfall: 0 0 0
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny Clear Sunny
Temperatures: 33 to 38 deg. F. 10 to 15 deg. F. 37 to 42 deg. F.
Ridge Top Winds: East and northeast East East
Wind Speed: 25 to 35 mph with gusts to 75 mph decreasing to 60 mph in the afternoon 10 to 15 mph with gusts to 30 mph 15 to 25 mph with gusts to 35 mph in the afternoon
Expected snowfall: 0 0 0
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