THIS AVALANCHE FORECAST EXPIRED ON December 12, 2019 @ 6:58 am
Avalanche Forecast published on December 11, 2019 @ 6:58 am
Issued by Steve Reynaud - Tahoe National Forest

MODERATE avalanche danger will continue in near and above treeline areas due to wind slabs. Storm slabs are becoming unlikely, with LOW avalanche danger in below treeline areas. 

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 SW winds yesterday began transporting snow and forming new wind slabs and cornices.  SW winds continued overnight and are forecasted to remain strong to gale force through today.  New unstable wind slabs are expected in near and above treeline terrain on NW-N-NE-E-SE aspects.  These wind slabs could be large enough to injure or bury a backcountry user. 

Look for blowing snow, new cornice formation, and snow surface scouring as clues to where new wind slabs will exist.  Avoid travel below large cornices and steep wind loaded terrain.

 

 

Avalanche Problem 2: Storm Slab
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Buried surface hoar below the 12/6-12/8 storm snow has been responsible for 1 snowboarder triggered avalanche on Monday and thought to be responsible for a handful of natural avalanches near the end of the storm cycle on Sunday.  This weak layer has been found in isolated areas and is thought to have only been reactive in the Donner Summit area.  Continued snowpack tests and observations have found this layer to be gaining strength with stubborn to non-reactive snowpack test results in most areas sampled. 

While isolated on a regional forecast scale, it’s not impossible that this weak layer and storm slab combination could still be encountered.  It has been found on Northerly aspects, above 8000', in below treeline, or wind protected near treeline terrain.  Even though this storm slab avalanche problem has become unlikely, safe travel protocols and good group decision making still apply.     

recent observations
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* Dec. 9 - Castle/Basin Peak Avalanche Incident Report

* Observations from the recent avalanche incident showed decomposing surface hoar gaining strength.  Snowpack tests showed stubborn to non-reactive results.

* Strong SW winds yesterday were transporting snow along the ridges above 8500'.  New wind slab and cornice formation were observed.

* A variety of crusts and wet snow exists on southerly aspects.  Cold winter snow can still be found on northerly aspects.

Weather and CURRENT CONDITIONS
weather summary

Unsettled weather will continue through the weekend.  A trace of new snow overnight fell at the upper elevations.  Wind gusts will be in the 40-50mph range over the ridges and could increase into Thursday.  Additional moisture will move into our area tonight with warm temperatures and rising snow levels.  Snow levels are forecasted to go to 8500-9000' for Thursday before decreasing into Friday night.  

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 27 to 31 deg. F.
Max. temperature: 44 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 30 to 45 mph
Maximum ridgetop wind gust: 64 mph
New snowfall: Trace inches
Total snow depth: 44 to 53 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy. Slight chance of rain. Snow levels 7500 feet. Chance of precipitation is 10%. Mostly cloudy. Chance of rain. Snow levels 7500 feet. Chance of precipitation is 35%. Mostly cloudy. Rain likely through the day. Snow levels 8500 feet. Chance of precipitation is 60%.
Temperatures: 37 to 42. deg. F. 28 to 33. deg. F. 41 to 46. deg. F.
Mid Slope Winds: Southwest 15 to 25 mph with gusts to 35 mph. Southwest 15 to 25 mph with gusts to 40 mph. Southwest 15 to 30 mph with gusts to 45 mph.
Expected snowfall: No accumulation. | SWE = less than 0.10 inch. No accumulation. | SWE = less than 0.10 inch. No accumulation. | SWE = up to 0.20 inch.
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy. Slight chance of snow in the afternoon. Snow levels 7500 feet. Chance of precipitation is 10%. Mostly cloudy. Chance of snow through the night. Chance of rain after midnight. Snow levels 7500 feet. Chance of precipitation is 35%. Mostly cloudy. Rain and snow likely. Snow levels 8500 feet. Chance of precipitation is 60%.
Temperatures: 34 to 39. deg. F. 26 to 31. deg. F. 38 to 43. deg. F.
Ridge Top Winds: Southwest 20 to 30 mph with gusts to 60 mph. Southwest 20 to 35 mph with gusts to 60 mph increasing to 30 to 45 mph with gusts to 85 mph after midnight. Southwest 30 to 50 mph with gusts to 95 mph.
Expected snowfall: 70% probability no accumulation. 30% probability up to 1 inch. | SWE = less than 0.10 inch. 60% probability no accumulation. 40% probability up to 2 inches. | SWE = less than 0.10 inch. 60% probability up to 3 inches. 30% probability no accumulation. | SWE = up to 0.15 inch.
Disclaimer

This avalanche forecast is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This forecast 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 forecast applies only to backcountry areas outside established ski area boundaries. This forecast describes general avalanche conditions and local variations always occur. This forecast expires 24 hours after the posted time unless otherwise noted. The information in this forecast is provided by the USDA Forest Service who is solely responsible for its content.

For a recorded version of the avalanche forecast call (530) 587-3558 x258