THIS AVALANCHE FORECAST EXPIRED ON December 7, 2019 @ 6:57 am
Avalanche Forecast published on December 6, 2019 @ 6:57 am
Issued by Brandon Schwartz - Tahoe National Forest

CONSIDERABLE avalanche danger for today in above treeline and near treeline areas due to a wind slab avalanche problem from increasing amounts of pre-storm blowing and drifting snow. Areas of MODERATE avalanche danger may exist as wind slabs form in wind exposed areas below treeline due to the strength of the winds. Numerous wind slab avalanches occurred yesterday and the avalanche problem will become more widespread today.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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If you see blowing and drifting snow, think unstable wind slabs. Mid slope and ridgetop winds are increasing again out of the S to SSW today with speeds of 45 to 70 mph expected today and 100 mph forecast for tonight. Unstable wind slabs existed yesterday and new ones will form on top of them today. Plenty of soft snow remains above 8,000' in most ridgetop areas to be drifted and deposited as new unstable wind slabs pre-storm today.

With the S to SSW winds, wind slabs from either direct loading or cross-loading are expected in near and above treeline terrain on W-NW-N-NE-E-SE aspects above about 7,500' to 8,000'. Avalanche size is expected at D1.5 to D2. The potential exists for some wind slabs to form along below treeline ridges and spines due to the strength of the winds. Once new snow starts falling tonight, avalanche size and distribution is expected to further increase.

Figure out where the wind slabs are and avoid them. Unstable wind slabs are likely on slopes where blowing and drifting snow is depositing, below cornices, and in areas were rounded bulges (wind pillows) exist on the upper to the middle portion of slopes. Increase your margin of safety in any place where these clues for unstable wind slabs exist.

recent observations
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Natural and human triggered wind slab avalanches were reported yesterday from Round Top (Carson Pass area), Red Lake Peak (Carson Pass area), and Grouse Rock (Ward Canyon area). All of these avalanches occurred in above treeline or near treeline terrain on N-NE-E aspects where S to SSW wind had drifted and deposited snow Wednesday night. These avalanches failed 6 to 18 inches deep in the snowpack.

The middle and bottom portions of the snowpack have continued to gain strength and are in good condition to handle new snow loading. Avalanches that occur today and tomorrow are expected to have snowpack failure occurring in the upper portion of the snowpack.

In recent days, a variety of surface crusts have been noted below 7,500' to 8,000' with softer surface snow above 8,000'.

Weather and CURRENT CONDITIONS
weather summary

Ridgetop winds are increasing out of the S ahead of the approaching storm system. Strong winds are expected today with gale force winds tonight and tomorrow. Timing for onset of the storm continues to slow down with snowfall now expected to begin over the forecast area between 8 pm and 10 pm tonight. Forecast snowfall amounts tonight through Sunday are 1 to 3 feet above 7,000'. Snow levels are forecast to fluctuate between 6,000' and 7,000' leading to a wide variance in potential snow accumulation in the 6,000' to 7,000' zone at 2 to 12 inches. For the latest info on the approaching storm, check the Winter Storm Warning from NWS Reno.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 25 to 28 deg. F.
Max. temperature: 32 to 33 deg. F.
Average ridgetop wind direction: S
Average ridgetop wind speed: 26 mph
Maximum ridgetop wind gust: 58 mph
New snowfall: 0 inches
Total snow depth: 33 to 52 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Cloudy. Chance of snow and rain. Snow levels below 7000 feet increasing to 7000 feet after midnight. Chance of precipitation is 90%. Cloudy. Snow and rain. Snow levels 7000 feet. Chance of precipitation is 95%.
Temperatures: 36 to 41. deg. F. 26 to 31. deg. F. 34 to 39. deg. F.
Mid Slope Winds: Southwest 15 to 25 mph with gusts to 45 mph. South 20 to 35 mph with gusts to 50 mph. South 25 to 35 mph with gusts up to 70 mph.
Expected snowfall: No accumulation. | SWE = none. 60% probability of 1 to 5 inches. 40% probability of 4 to 8 inches. | SWE = up to 0.45 inch. 70% probability of 4 to 8 inches. 30% probability of 6 to 12 inches. | SWE = 0.55-1.05 inches.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Cloudy. Chance of snow in the evening, then snow after midnight. Snow levels below 7000 feet increasing to 7000 feet after midnight. Chance of precipitation is 85%. Cloudy. Snow. Snow levels 7000 feet. Chance of precipitation is 95%.
Temperatures: 32 to 37. deg. F. 24 to 29. deg. F. 30 to 35. deg. F.
Ridge Top Winds: South 30 to 45 mph with gusts to 70 mph. South 35 to 55 mph with gusts to 100 mph. Southwest 40 to 60 mph with gusts to 100 mph.
Expected snowfall: No accumulation. | SWE = none. 70% probability of 2 to 5 inches. 30% probability of 4 to 8 inches. | SWE = 0.20-0.45 inch. 60% probability of 8 to 12 inches. 40% probability of 12 to 18 inches. | SWE = 0.70-1.15 inches.
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