THIS AVALANCHE FORECAST EXPIRED ON December 20, 2019 @ 6:55 am
Avalanche Forecast published on December 19, 2019 @ 6:55 am
Issued by Brandon Schwartz - Tahoe National Forest

MODERATE avalanche danger continues for above treeline and near treeline terrain due to wind slabs formed yesterday from deposits of wind drifted snow. Significant uncertainty exists for near treeline terrain where a wind slab avalanche yesterday was observed to have unusual characteristics. Below treeline, LOW avalanche danger continues.

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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Yesterday's SW winds drifted significant amounts of snow in near treeline and above treeline terrain. Newly formed wind slabs exist on NW-N-NE-E-SE aspects. The expected avalanche size is up to D2.

A natural wind slab avalanche with unusual characteristics was observed yesterday on Elephants Hump (Carson Pass Area). This hard slab avalanche occurred in near treeline terrain on a N aspect at 8,400'. The 1 to 1.5 foot crown propagated around a corner to be about 200' feet wide in relatively small avalanche terrain. Additional shooting cracks were observed off the edge of the crown. Additional human triggered collapses were reported yesterday in the area adjacent to the crown of the avalanche. The characteristics of this avalanche suggest that there may have been faceted (sugary) snow or surface hoar underneath the wind slab. 

Greater than usual uncertainty warrants extra caution around wind slabs today. Hard slab conditions exist above treeline. Near treeline wind slabs may avalanche wider than anticipated. Use the clues of recently wind drifted snow to identify areas of wind slab and adjust routes accordingly. Recently wind drifted snow exists below cornices, at and below rounded wind pillows, and were indicated by wind scouring vs deposition patterns along ridgelines.

 Photos of yesterday's hard wind slab avalanche. Note how the debris in the trees of the first photo extend well around the corner and continue out of view.

recent observations
Submit Observations

Significant amounts of blowing and drifting snow were observed near treeline and above treeline yesterday in the Carson Pass area with one natural wind slab avalanche reported. Lesser amounts of blowing snow were reported from the Mount Rose and Donner Summit areas. Recent observations from around the forecast area have noted near surface facets and surface hoar in wind protected areas below treeline. The larger open areas have held the most well developed near surface facets and the largest surface hoar. Snowpit tests targeting the buried Dec 12 rain crust have yet to show problematic weak layer formation around this crust.

Weather and CURRENT CONDITIONS
weather summary

The weak weather system that brought SW winds and a trace of snowfall is on the way out of the forecast area. High pressure will build for this afternoon and last through Friday. The next storm system is expected to impact the region late Saturday night into Monday morning. Ridgetop winds decreased overnight but will remain moderate speed out of the SW today and tomorrow. Winds will increase again late Friday into Saturday ahead of the next storm system.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 20 to 26 deg. F.
Max. temperature: 26 to 29 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 38 mph
Maximum ridgetop wind gust: 78 mph
New snowfall: 0 to trace inches
Total snow depth: 45 to 50 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy. Slight chance of snow showers in the morning. Snow levels below 7000 feet. Chance of precipitation is 10%. Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 34 to 39. deg. F. 23 to 28. deg. F. 38 to 43. deg. F.
Mid Slope Winds: Light winds becoming southwest around 15 mph in the afternoon. Gusts up to 25 mph. Southwest around 15 mph with gusts to 35 mph. Southwest around 15 mph with gusts to 35 mph.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. No accumulation. | SWE = none.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 10%. Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%. Partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 30 to 35. deg. F. 21 to 26. deg. F. 34 to 39. deg. F.
Ridge Top Winds: Southwest around 15 mph with gusts to 30 mph. Southwest 15 to 20 mph with gusts to 35 mph. Southwest 15 to 25 mph with gusts to 35 mph.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. No accumulation. | SWE = none.
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