THIS AVALANCHE FORECAST EXPIRED ON December 20, 2017 @ 6:56 am
Avalanche Forecast published on December 19, 2017 @ 6:56 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

LOW avalanche danger will continue today. While triggering an avalanche remains unlikely, following safe travel protocols when in and around avalanche terrain remains a prudent choice. A winter storm forecasted to move into the area tonight and tomorrow will cause the avalanche danger to increase tomorrow and human triggered wind slab and storm slab avalanches may become an issue. If the storm moves in faster than expected, the avalanche danger could increase tonight. 

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Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Near Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Normal Caution
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Today's avalanche problems look similar to yesterday's. A few areas of unstable snow may still exist on isolated terrain features in the form of hard wind slabs on top of weak snow in pockets of near and above treeline terrain and soft slabs on weak snow in small areas on northerly aspects below treeline (especially in the southern part of the forecast area). Triggering one of these instabilities remains unlikely today.  Firm icy snow surfaces still exist on most exposed near and above treeline exposed slopes.  A fall or a slip could be hard to arrest on these slopes in steeper terrain.  Numerous obstacles and hazards still remain exposed or barely covered. 

The incoming storm will bring increased avalanche hazard for tomorrow. The new snow will fall on top of a variety of firm surfaces and weak snow. Expect to see wind slab and storm slab avalanche problems across the forecast area tomorrow. Wind slabs will start to form as soon as snowfall starts to accumulate after midnight tonight. Since the forecast calls for the bulk of the accumulation to occur between early and mid-morning tomorrow, these wind slabs should remain small during the night. By mid-morning tomorrow, they may have grown to a problematic size. Storm slabs should follow a similar pattern: starting to form overnight as the snowfall starts but not becoming large enough to pose problems until the peak of the accumulation tomorrow morning. IF the storm moves faster than expected and most of the accumulation occurs tonight instead of early to mid-morning tomorrow, the avalanche danger could rise during the night. If for some reason you have to travel in the backcountry during the night or very early tomorrow morning, check the Reno NWS page and the remote weather pages for updated forecasts and conditions to see if the storm arrived faster than forecasted.

recent observations
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* Firm, wind scoured snow surfaces and exposed rain crusts exist on most aspects in near and above treeline terrain.

* Variable snow surfaces with some lingering areas of softer snow exist in near and below treeline shaded and wind protected areas.

* Snowpack tests continue to point to isolated areas of instabilities throughout the forecast region.  Hard wind slabs over weak loose snow (facets) in near treeline and above treeline terrain and soft slabs over weak faceted snow in below treeline terrain.

* Decent snow coverage still exists in areas north of Emerald Bay above 8,000'. Below 8,000' snow coverage remains patchy and shallow. South of Emerald Bay, less snow exists with areas below 8,500' holding very little snow.  Snow coverage on southerly aspects has become intermittent and highly variable depending on location.

Weather and CURRENT CONDITIONS
weather summary

Winds have shifted to the southwest and increased ahead of a fast-moving, cold storm approaching the area. Cloud cover should also increase today. This storm should move into the region during night and remain through tomorrow. The forecast calls for 3 to 5 inches of new snow in most areas with up to 10 inches possible in some places above 7000 ft. Most of this snow should accumulate during the peak of the storm between 1 am and 10 am on Wednesday, but snowfall could linger into the afternoon tomorrow. By tomorrow evening, the storm should begin to depart leaving cold, dry, windy weather in its wake. 

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 35 to 40 deg. F.
Max. temperature: 48 to 56 deg. F.
Average ridgetop wind direction: Southwest
Average ridgetop wind speed: Before midnight: 5 to 15 mph | After midnight: 20 to 30 mph
Maximum ridgetop wind gust: 42 mph
New snowfall: 0 inches
Total snow depth: 15 to 32 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Partly cloudy Partly cloudy becoming mostly cloudy with scattered snow showers after midnight Cloudy with widespread snow showers in the morning. Snow showers likely in the afternoon
Temperatures: 42 to 47 deg. F. 23 to 28 deg. F. 26 to 31 deg. F.
Mid Slope Winds: Southwest Southwest Northwest
Wind Speed: 10 to 15 mph with gusts to 35 mph increasing to 20 to 30 mph with gusts to 60 mph in the afternoon 25 to 35 mph with gusts to 90 mph 20 to 35 mph with gusts to 85 mph decreasing to 50 mph in the afternoon
Expected snowfall: 0 up to 2 2 to 4
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Partly cloudy Partly cloudy becoming mostly cloudy with scattered snow showers after midnight Cloudy with widespread snow showers in the morning. Snow showers likely in the afternoon
Temperatures: 39 to 44 deg. F. 20 to 25 deg. F. 23 to 29 deg. F.
Ridge Top Winds: Southwest Southwest Southwest shifting to northwest in the afternoon
Wind Speed: 20 to 30 mph with gusts to 60 mph increasing to 30 to 45 mph with gusts to 90 mph this afternoon 45 to 65 mph with gusts to 90 mph increasing to 130 mph after midnight 40 to 60 mph with gusts to 125 mph decreasing to 25 to 35 mph with gusts to 65 mph in the afternoon
Expected snowfall: 0 up to 2 3 to 5
Disclaimer

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

For a recorded version of the Avalanche Advisory call (530) 587-3558 x258