THIS AVALANCHE FORECAST EXPIRED ON December 9, 2018 @ 6:45 am
Avalanche Forecast published on December 8, 2018 @ 6:45 am
Issued by Brandon Schwartz - Tahoe National Forest

Avalanche danger has risen to MODERATE danger near treeline and above treeline. Increased SW winds last night may have created new wind slabs and loaded the Dec 4 buried surface hoar layer. LOW avalanche danger exists below treeline.

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
  • Size ?
    Historic
    Very Large
    Large
    Small

SW winds increased last night and became just strong enough to move snow. Plenty of unconsolidated snow existed along the ridgetops and was available for redistribution through wind transport. A fair bit of uncertainty exists as to the depth and extent of newly formed wind slabs. Any areas where new wind slabs have been deposited on top of the Dec 4 buried surface hoar layer could be very problematic. The vast majority of new wind slabs are expected near treeline and above treeline on NW-N-NE-E-SE aspects. Avalanche size in isolated areas could be large enough to bury a person (size D2), but is mostly expected to be too small to bury a person (size D1).

Look for signs of newly wind drifted snow in the form of wind pillows, wind textured snow surfaces, and cornice formation. Carefully evaluate slopes before committing. Keep in mind that a surface hoar weak layer may fail on lower angle slopes than a more typical uncomplicated wind slab. Avalanches may be triggered lower on a slope than usual and propagation may be quite wide. If evidence pointing to safe conditions is limited and uncertainty remains, opt for more wind protected terrain. Simply avoiding all wind affected areas is an easy way to manage today's avalanche problem.

recent observations

* Observations made yesterday on West Grouse (Ward canyon area) and on Tamarack Peak (Mount Rose area) matched well with other recent observations from around the forecast area showing the Dec 4 surface hoar layer buried within the top 3 to 6 inches of the snowpack in many but not all areas.

* Snowpit tests performed in the West Grouse area similating a 4 inch new slab load on top the the existing snowpack created easy failure and propagation along the Dec 4 surface hoar layer on both NE and SE aspects.

* Decent snow coverage exists above 7,000' to 7,500' along the Sierra Crest with the best coverage in the northern and far southern Sierra Crest portions of the forecast area.  Snow coverage declines to the east.  Early season conditions exist.

Weather and CURRENT CONDITIONS
weather summary

Weak high pressure continues to build over the forecast area. Sunny skies, a warming trend,  and SW winds are the result. Some low clouds still linger under inversion conditions in some of the valleys, but sunshine is generally expected today for mountain locations. SW winds picked up last night. Ridgetop winds are expected to lull today before increasing further tonight and tomorrow.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 18 to 28 deg. F.
Max. temperature in the last 24 hours: 31 to 40 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 20 mph
Maximum wind gust in the last 24 hours: 37 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 29 to 36 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Mostly sunny. Snow levels below 7000 feet. Chance of precipitation is 0%. Increasing high clouds. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures: 37 to 42. deg. F. 19 to 25. deg. F. 36 to 41. deg. F.
Mid Slope Winds: Light winds. Light winds. Southwest 10 to 15 mph with gusts to 35 mph.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. No accumulation. | SWE = none. in.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%. Increasing high clouds. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures: 35 to 40. deg. F. 18 to 23. deg. F. 32 to 37. deg. F.
Ridge Top Winds: Southwest 15 to 20 mph with gusts to 40 mph in the morning becoming light. South 15 to 20 mph. Gusts up to 30 mph increasing to 40 mph after midnight. Southwest 15 to 30 mph. Gusts up to 45 mph increasing to 55 mph in the afternoon.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. No accumulation. | SWE = none. 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.

For a recorded version of the Avalanche Advisory call (530) 587-3558 x258