THIS AVALANCHE ADVISORY EXPIRED ON January 2, 2015 @ 6:58 am
Avalanche Advisory published on December 31, 2014 @ 6:58 am
Issued by Brandon Schwartz - Tahoe National Forest

Pockets of MODERATE avalanche danger linger in recently wind loaded areas near and above treeline on slopes 35 degrees and steeper. In near treeline areas, pockets of recently formed wind slabs exist on all aspects. Above treeline, recently formed wind slabs are focused more on SE-S-SW-W-NW aspects. Below treeline, avalanche danger remains LOW.

The next scheduled update to this advisory will occur January 2, 2015 at 7am.

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
  • Type ?
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  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Newly formed wind slabs 6 inches to 2 feet deep exist in a variety of lee areas both near and above treeline. In above treeline areas, wind slab location has proven more predictable with less interruption to wind direction. In near treeline areas, swirling winds created pockets of both deposition and scouring on all aspects. This created pockets of wind slab formation on all aspects near treeline. Human triggered avalanches remain possible, with increased difficulty of triggering expected going into the new year.

Keep in mind that while increased difficulty of triggering is an indication of increasing stability, it also means that detecting lingering pockets of instability becomes increasingly challenging. Slope by slope stability evaluation and one at a time travel from one well defined island of safety to another are wise choices when managing challenging to detect lingering instability. 

recent observations

December 30th observations both made and received from the Mount Rose, Carson Pass, and Donner Summit areas revealed gale force winds, wind transport of snow, and subsequent wind slab formation. Wind slabs were noted in a variety of areas with the most predictable placement above treeline and less predictable placement near treeline due to swirling winds. Skier triggered cracking was noted in areas of wind slab formation. Slab depth ranged from 6 inches to 2 feet. Snowpack failure was noted to occur either within the wind deposited snow or at the old/new snow interface. All failures were noted to occur at or above the uppermost rain crust within the snowpack.

Weather and CURRENT CONDITIONS
weather summary

The cold front that passed through the forecast area Dec 30th deposited new snow amounts ranging from 1 to 4 inches over the last 24 hours. This brought 36 hour storm totals up to 2 to 8 inches. Cold air behind the front is expected to warm Wednesday night and Thursday as high pressure builds over the region. East to northeast ridge top winds will gradually decrease in speed through New Year's Eve into New Year's Day.

For the morning of the 31st, remote sensors are reporting 6am air temperatures in the low single digits on either side of 0 F for all elevations. Maximum daytime air temperatures above 7,000' are forecast to reach the low teens to low 20s. Gale force east to northeast ridgetop winds are on a gradual slowing trend with moderate to strong winds expected through New Year's Eve.

Going in to the new year, mid and upper elevation air temperatures both day and night are forecast to increase 10 to 15 deg F Wednesday night into Thursday. Maximum daytime air temperatures above 7,000' are forecast to reach the upper 20s to low 30s on New Year's Day. Easterly ridgetop winds are forecast to decrease to light to moderate in speed by the afternoon on New Year's Day.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 0 to 5 deg. F.
Max. temperature in the last 24 hours: 11 to 16 deg. F.
Average wind direction during the last 24 hours: East
Average wind speed during the last 24 hours: 49 mph
Maximum wind gust in the last 24 hours: 88 mph
New snowfall in the last 24 hours: 1 to 4 inches
Total snow depth: 29 to 42 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Wednesday Wednesday Night Thursday
Weather: Sunny skies. Clear skies. Sunny skies.
Temperatures: 18 to 23 deg. F. 11 to 18 deg. F. 26 to 31 deg. F.
Wind Direction: NE to E E E
Wind Speed: 20 to 35 mph with gusts to 45 mph, decreasing to 15 to 25 mph with gusts to 40 mph in the afternoon. 10 to 20 mph with gusts to 30 mph. 10 to 15 mph with gusts to 25 mph in the morning, becoming light.
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Sunny skies. Clear skies. Sunny skies.
Temperatures: 13 to 18 deg. F. 15 to 20 deg. F. 27 to 32 deg. F.
Wind Direction: E to NE NE NE
Wind Speed: 45 to 55 mph with gusts to 85 mph, decreasing to 35 to 45 mph with gusts to 70 mph in the afternoon. 30 to 40 mph with gusts to 60 mph, decreasing to 20 to 30 mph with gusts to 50 mph after midnight. 20 to 25 mph with gusts to 40 mph, decreasing to 10 to 15 mph with gusts to 35 mph in the afternoon.
Expected snowfall: 0 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.