THIS AVALANCHE FORECAST EXPIRED ON December 8, 2019 @ 6:59 am
Avalanche Forecast published on December 7, 2019 @ 6:59 am
Issued by Brandon Schwartz - Tahoe National Forest

An increase to HIGH avalanche danger is expected today in near treeline and above treeline areas due to new snow and wind drifted snow creating wind slabs and the potential for large avalanches. CONSIDERABLE avalanche danger is expected below treeline due to high intensity snowfall creating storm slabs. Travel in near treeline and above treeline avalanche terrain is not recommended. Travel in below treeline avalanche terrain will become increasingly dangerous as the day progresses. Lighting strikes are possible this afternoon.

4. High

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Above Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

4. High

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Near Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
Avalanche Problem 1: Wind Slab
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New snow and wind today is forming new wind slabs on top of the older wind slabs formed by wind drifted snow on the ground over the past two days. This avalanche problem exists mainly near treeline and above treeline on NW-N-NE-E-SE aspects. Some avalanches could be large and destructive up to a size D3, especially if breaking into the older deeper wind slabs. Isolated wind slabs may form below treeline in wind exposed areas along ridgelines and spines due to the strength of the winds.

Travel in near treeline to above treeline avalanche terrain is not recommended.

Avalanche Problem 2: Storm Slab
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As this storm progresses, a storm slab avalanche problem is expected to become increasingly likely in wind protected areas below treeline on all aspects. Periods of high intensity snowfall may create storm slab instability. There is uncertainty about the burial of surface hoar that may have persisted yesterday in wind protected areas below treeline. In any place where this occurred, increased sensitivity to triggering of storm slabs is expected today.

Any signs of natural avalanche activity or snow surface cracking in wind protected areas below treeline indicate the presence of unstable storm slabs in the immediate area. If this is the case, seek low angle terrain without steeper terrain above. Keep in mind that poor visibility may make finding safe areas difficult without excellent terrain familiarity or proper use of navigation tools.

recent observations
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Several wind slab avalanches both natural and human triggered were reported on Thursday from drifting snow under sunny skies. These avalanches occurred above 8,000' on N-NE-E aspects in near treeline and above treeline terrain. Increasing winds yesterday along the Sierra Crest and in the Luther Pass area were noted to create additional areas of drifting snow, likely increasing the size of existing wind slabs.

Below 8,000' the existing snowpack is in good condition to handle rain on snow. Above 8,000' the bottom and middle portions of the snowpack are strong. Snowpack failure is expected to occur either within the upper portion of the existing snowpack (old wind slabs) or within the new snow (new wind slabs or storm slabs).

Weather and CURRENT CONDITIONS
weather summary

The current storm system will impact the forecast area today and tomorrow. Precipitation will move through in two main waves. The first wave this morning is seeing snow levels rising up to around 7,500'. The second more intense wave is forecast to move through around 4 to 6 pm, lowering snow levels to around 6,000' and providing some lightning strikes. By noon tomorrow, storm total new snow amounts of 1 to 3 feet are expected above 7,000' from 1.5 to 2.5 inches of snow water equivalent (SWE). Ridgetop winds out of the SW increased to strong to gale force in speed overnight. Gale force winds are forecast to continue through tonight, decreasing to moderate speed tomorrow. The second wave of precipitation later today will usher in an air temperature cooling trend for tonight and 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: 30 to 32 deg. F.
Max. temperature: 31 to 36 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 44 mph
Maximum ridgetop wind gust: 109 mph
New snowfall: 3 to 9 inches
Total snow depth: 36 to 53 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy. Snow and rain throughout the day. Chance of thunderstorms in the afternoon. Snow levels 7500 feet. Chance of precipitation is 100%. Cloudy. Chance of thunderstorms in the evening. Snow through the night. Snow levels below 7000 feet. Chance of precipitation is 100%. Cloudy. Snow in the morning, then snow likely in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 75%.
Temperatures: 34 to 39. deg. F. 26 to 32. deg. F. 28 to 33. deg. F.
Mid Slope Winds: Southwest 20 to 30 mph with gusts to 60 mph. Southwest 20 to 35 mph with gusts to 70 mph. Southwest 15 to 25 mph. Gusts up to 40 mph in the morning.
Expected snowfall: 70% probability of 5 to 10 inches. 30% probability of 4 to 8 inches. | SWE = 0.65-1.10 inches. 70% probability of 7 to 12 inches. 30% probability of 12 to 16 inches. | SWE = 0.75-1.25 inches. 70% probability up to 3 inches. 30% probability of 3 to 6 inches. | SWE = up to 0.20 inch.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy. Snow. Chance of thunderstorms in the afternoon. Snow levels 7500 feet. Chance of precipitation is 100%. Cloudy. Chance of thunderstorms in the evening. Snow through the night. Snow levels below 7000 feet. Chance of precipitation is 100%. Cloudy. Snow in the morning, then snow likely in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 80%.
Temperatures: 30 to 35. deg. F. 23 to 28. deg. F. 24 to 29. deg. F.
Ridge Top Winds: Southwest 40 to 50 mph with gusts to 100 mph. Southwest 40 to 60 mph with gusts to 110 mph decreasing to 30 to 50 mph with gusts to 95 mph after midnight. Southwest 20 to 35 mph decreasing to 15 to 25 mph in the afternoon. Gusts up to 60 mph.
Expected snowfall: 70% probability of 8 to 14 inches. 30% probability of 5 to 10 inches. | SWE = 0.80-1.30 inches. 70% probability of 8 to 14 inches. 30% probability of 12 to 18 inches. | SWE = 0.85-1.30 inches. 70% probability of 1 to 3 inches. 30% probability of 3 to 6 inches. | SWE = up to 0.20 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