THIS AVALANCHE ADVISORY EXPIRED ON February 8, 2014 @ 5:54 am
Avalanche Advisory published on February 7, 2014 @ 5:54 am
Issued by Brandon Schwartz - Tahoe National Forest

Areas of MODERATE avalanche danger will form today near and above treeline on the NW-N-NE-E-SE aspects on slopes 35 degrees and steeper as wind slabs continue to build. As higher intensity precipitation impacts the forecast area this evening through the overnight hours, avalanche danger is expected to increase to HIGH danger.

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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Strong winds today will scuplt new snow and wind transported old into wind slabs of increasing size. These new wind slabs will build on top of the small but unstable wind slabs that existed yesterday. Human triggered avalanches are possible today in near and above treeline terrain on NW-N-NE-E-SE aspects.

Avalanche Problem 2: Persistent Slab
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In areas above 9,500' persistent slabs linger near treeline and below treeline on NW-N-NE aspects. Weak layers of well developed facets and depth hoar remain buried in the snowpack in these areas and were not destroyed by rain on January 28 and 29. The likelihood of failure of these basal facets will increase as this storm cycle progresses and additional new snow load stresses the snowpack above these weak layers. Locations that are both above 9,500' and near treeline or below treeline terrain represent only a small portion of the forecast area, keeping this problem isolated in distribution.

recent observations

Observations made yesterday on Carpenter Ridge (Independence Lake area) and near Grouse Rocks (Ward Canyon area) revealed small shallow wind slabs in lee areas and several weak layers within the upper snowpack on NW-N-NE aspects. Wind slabs were limited to 4 inches thick or less and generally extended less than 20 feet down slope. These wind slabs failed easily in response to the weight of a skier, producing shooting cracks and tiny avalanches. Upper snowpack weak layers consist of buried surface hoar, buried graupel layers, and/or near crust facets on top of the prominent January 30 rain crust. These weak layers have been observed in many locations around the forecast area over the past several days. The distribution of each of these weak layers varies around the forecast area, but generally 1 to 2 of these weak layers can be found in the upper snowpack on most NW-N-NE aspects. The presence of these weak layers has the existing snowpack in poor condition to handle new snow loading.

Weather and CURRENT CONDITIONS
weather summary

A strong pacific storm system is moving into the forecast area. Southwest winds increased last night with ridgetop gusts to 74 mph recorded. Light snowfall over the past 24 hours has allowed 3 to 4 inches of new snow to accumulate above 7,000', with most of that falling last night. Light snowfall is forecast to continue today with 1 to 4 inches of accumulation expected. Snowfall intensity will increase this evening through the overnight hours with 6 to 12 inches of new snow expected above 6,000'. Gale force ridgetop winds are expected tonight into tomorrow. Air temperatures are expected to follow a gradual warming trend over the next several days.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 20 to 25 deg. F.
Max. temperature in the last 24 hours: 25 to 32 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 37 mph
Maximum wind gust in the last 24 hours: 74 mph
New snowfall in the last 24 hours: 3 to 4 inches
Total snow depth: 18 to 34 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Cloudy skies with scattered snow showers in the morning. Snow likely in the afternoon. Cloudy skies with snow. Cloudy skies with snow. A mix of rain and snow possible.
Temperatures: 26 to 32 deg. F. 22 to 27 deg. F. 33 to 40 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 20 to 30 mph with gusts to 50 mph 25 to 35 mph with gusts to 65 mph. 45 to 55 mph with gusts to 80 mph.
Expected snowfall: 1 to 4 in. 6 to 10 in. 4 to 8 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Cloudy skies with scattered snow showers in the morning. Snow likely in the afternoon. Cloudy skies with snow. Cloudy skies with snow.
Temperatures: 20 to 26 deg. F. 18 to 25 deg. F. 21 to 28 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 50 to 60 mph with gusts to 90 mph. 65 to 75 mph with gusts to 110 mph. 65 to 75 mph with gusts to 105 mph.
Expected snowfall: 2 to 4 in. 6 to 12 in. 4 to 8 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.