THIS AVALANCHE FORECAST EXPIRED ON December 22, 2019 @ 6:45 am
Avalanche Forecast published on December 21, 2019 @ 6:45 am
Issued by Brandon Schwartz - Tahoe National Forest

MODERATE avalanche danger continues above treeline and near treeline due to a variety of difficult to trigger hard and soft wind slabs. LOW avalanche danger exists in wind protected areas 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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SW winds have drifted snow and deposited it as wind slabs in above treeline and near treeline terrain. Wind slabs ranging from soft slab to hard slab are widespread on NW-N-NE-E-SE aspects. Old snow on the ground that is still available for drifting is minimal. Older wind slabs formed during the Dec 18 wind event are gaining strength.

At this point, wind slabs exist in most all lee areas near treeline and above treeline but are difficult to trigger. Any avalanches that occur today will most likely be isolated and in an area surrounded by seemingly good stability. Avalanche size up to D2 remains possible. While triggering one of the older hard wind slabs over softer near surface facets from Dec 18 has become unlikely, the consequences of doing so remain elevated.

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 where indicated by wind scouring vs deposition patterns along ridgelines.

recent observations
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Recent observations have shown a variety of hard and soft wind slabs in near treeline and above treeline terrain. In some areas, especially near treeline, wind slabs sit on top of a soft layer of near surface facets. Ongoing strength gains for these older wind slabs on near surface facets have been observed day to day. No new avalanches have been reported since Dec 18. Light to moderate amounts of drifting snow was observed yesterday along ridgelines. Wind protected areas below treeline continue to hold unconsolidated surface snow on shaded northerly aspects (near surface facets). Snowpit tests looking deeper into the snowpack have not identified any problematic weak layers beyond the wind slab over near surface facets structure.

Weather and CURRENT CONDITIONS
weather summary

Sunny, warm, and windy today as strong S to SW winds continue ahead of the approaching storm. The timing of the start of snowfall has slowed a bit over the past 24 hours and expected new snow accumulation has decreased. Snowfall is now expected to begin tomorrow morning and end tomorrow evening. Snowfall amounts of 2 to 8 inches are expected with snow levels 5,000' to 5,500'. A second weather system passing by to the south on Monday may bring some light snow showers for areas south of I-80.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 33 to 39 deg. F.
Max. temperature: 35 to 42 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 48 mph
Maximum ridgetop wind gust: 74 mph
New snowfall: 0 inches
Total snow depth: 43 to 46 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%. Clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Sunny then becoming mostly cloudy. Chance of snow in the morning, then snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 80%.
Temperatures: 39 to 44. deg. F. 25 to 30. deg. F. 32 to 37. deg. F.
Mid Slope Winds: Southwest 20 to 30 mph increasing to 30 to 40 mph in the afternoon. Gusts up to 60 mph. South 25 to 40 mph with gusts to 60 mph. South 20 to 35 mph with gusts to 50 mph.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. 80% probability of 2 to 4 inches. 20% probability of 4 to 6 inches. | SWE = 0.20-0.45 inch.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy then becoming clear. Snow levels below 7000 feet. Chance of precipitation is 0%. Sunny then becoming mostly cloudy. Chance of snow in the morning, then snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 85%.
Temperatures: 35 to 40. deg. F. 23 to 28. deg. F. 28 to 33. deg. F.
Ridge Top Winds: South 35 to 55 mph with gusts to 85 mph. South 45 to 65 mph with gusts to 100 mph. South 35 to 55 mph with gusts to 90 mph.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. 80% probability of 2 to 5 inches. 20% probability of 5 to 7 inches. | SWE = 0.25-0.50 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