THIS AVALANCHE FORECAST EXPIRED ON December 30, 2019 @ 6:58 am
Avalanche Forecast published on December 29, 2019 @ 6:58 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

MODERATE avalanche danger still exists in near and above treeline terrain due to shifting winds and blowing snow. Slabs of wind drifted snow (wind slabs) could exist on almost any wind-exposed slope. The avalanche danger remains LOW in wind-protected 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 NE winds have left wind slabs on N-NW-W-SW-S-SE aspects. While these lingering hard slabs may be more difficult to trigger, a person could still cause them to release from the right spot (i.e. where the slab is thinner or over a trigger point). As the winds shift back to the SW and increase today, small slabs of wind drifted snow may form on NW-N-NE-E-SE aspects. These will grow some in size as new snow forecasted for this afternoon and tonight accumulates. Avalanches that involve enough snow to bury or injure a person (D2) remain possible today. 

Clues like blowing snow, scoured surfaces, firm hollow-sounding snow, sastrugi, drifted snow, and other wind created textures can help identify where wind slabs may exist. These exposed areas will also hold more variable and challenging snow conditions. Travel plans that focus on finding sheltered terrain are more likely to find soft unconsolidated snow.

 

Photos: Human-triggered wind slab avalanche from Dec 27. More info here.

recent observations
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* Exposed near and above treeline terrain held wind affected snow surfaces ranging from scoured icy crusts to sastrugi to hard wind slabs to softer wind drifted snow. Observers reported seeing blowing snow along ridgelines yesterday on the Sierra Crest and in the Mt. Rose backcountry. 

* Some human-triggered cracking and test slope failures occurred in the Donner Pass and Castle Peak areas yesterday. Some minor cracking also occurred in the Slab Cliffs area. 

* In sheltered below treeline areas near Ebbetts Pass, Luther Pass, Donner Summit, and in the Mt. Rose backcountry, soft snow still existed. Observers found some surface hoar but it had already fallen over and started to deteriorate in most places.

Weather and CURRENT CONDITIONS
weather summary

The strong ENE winds decreased overnight and started to shift to the WSW this morning around 4 am. This wind shift heralds the approach of a weak storm forecasted to bring increased SW winds and 2-4 inches of new snow to the area this afternoon and tonight. As the snow begins to taper off after midnight, the winds should shift back to the NE. Expect a cold day with NE winds tomorrow. 

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 26 to 34 deg. F.
Max. temperature: 30 to 39 deg. F.
Average ridgetop wind direction: ENE
Average ridgetop wind speed: 20 to 30 mph
Maximum ridgetop wind gust: 62 mph
New snowfall: 0 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.
Sunday Sunday Night Monday
Weather: Mostly cloudy. Chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 50%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 90%. Cloudy. Slight chance of snow in the morning. Snow levels below 7000 feet. Chance of precipitation is 20%.
Temperatures: 32 to 37 deg. F. 21 to 26 deg. F. 28 to 33 deg. F.
Mid Slope Winds: Southwest around 15 mph. Gusts up to 30 mph increasing to 40 mph in the afternoon. South around 15 mph shifting to the northeast after midnight. Gusts up to 30 mph. Northeast 15 to 20 mph with gusts to 45 mph.
Expected snowfall: 70% probability up to 1 inch. 30% probability of 1 to 3 inches. | SWE = less than 0.10 inch. 80% probability of 2 to 4 inches. 20% probability of 4 to 6 inches. | SWE = up to 0.20 inch. 20% probability up to 1 inch. 80% probability no accumulation. | SWE = less than 0.10 inch.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy. Chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 50%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 90%. Cloudy. Slight chance of snow in the morning. Snow levels below 7000 feet. Chance of precipitation is 25%.
Temperatures: 28 to 34 deg. F. 18 to 23 deg. F. 23 to 28 deg. F.
Ridge Top Winds: Southwest 15 to 25 mph. Gusts up to 30 mph increasing to 40 mph in the afternoon. South 15 to 25 mph shifting to the northeast 15 to 20 mph after midnight. Gusts up to 35 mph. Northeast 20 to 35 mph with gusts to 50 mph.
Expected snowfall: 70% probability up to 1 inch. 30% probability of 1 to 3 inches. | SWE = less than 0.10 inch. 80% probability of 2 to 5 inches. 20% probability of 5 to 7 inches. | SWE = 0.20-0.30 inch. 20% probability up to 1 inch. 80% probability no accumulation. | SWE = less than 0.10 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