THIS AVALANCHE ADVISORY EXPIRED ON March 21, 2016 @ 6:48 am
Avalanche Advisory published on March 20, 2016 @ 6:48 am
Issued by Brandon Schwartz - Tahoe National Forest

MODERATE avalanche danger exists today for all aspects both above and below treeline on slopes 35 degrees and steeper due to expected poor snow surface refreeze last night and rain on snow this afternoon. Increasingly hazardous avalanche conditions are expected this evening into tomorrow as wind slabs begin to form in near and above treeline areas on NW-N-NE-E-SE aspects.

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.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Loose Wet
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A poor snow surface refreeze is expected to have occurred last night in areas below 9,000' to 9,500'. Warm overnight air temperatures will have kept snow surface refreeze reliant on radiational cooling. In open areas below 9,000', snow surface refreeze that did occur is expected to be thin and superficial. Little to no snow surface refreeze is expected to have occurred in treed areas where the forest canopy inhibits significant radiational cooling. Rain on snow expected this afternoon will add additional free water to the snowpack. In many areas below 7,500' to 8,000', recent melt has established free water drainage from the snowpack and today's rain will drain from the snowpack fairly easily. In the 8,000' to 9,000' zone where free water drainage is not as well established, more loose wet instability could occur during rain on snow this afternoon, especially on W-NW-N-NE-E aspects.

Avalanche Problem 2: Wind Slab
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Strong to gale force SW winds and up to a few inches of new snow beginning to accumulate above 8,000' late today and tonight will start the formation of small wind slabs in near treeline and above treeline terrain. This avalanche problem is expected to become increasingly widespread on NW-N-NE-E-SE aspects above 7,000' to 8,000' as wind slabs build over the course of this storm cycle. Use clues such as signs of avalanche activity from the last storm cycle, cornice formations, wind pillows below ridgelines, and blowing snow to determine the location of potentially unstable wind slabs.

recent observations

Observations made yesterday on Ralston Peak (Echo Summit area) and while traversing the Sierra Crest between Sugar Bowl and Squaw Valley revealed differing degrees of snow surface melt from one area to another. Once the snow surface started to melt around 10:30 to 11 am, some areas became marginally skier supportable by mid day while other areas remain highly supportable, especially above 8,000'. By late in the afternoon, unsupportable deep wet snow was widespread on E-SE-S-SW-W aspects below 7,800'. In these mid and low elevation areas, well established free water drainage from the snowpack kept loose wet instability to a minimum.

Weather and CURRENT CONDITIONS
weather summary

Transitional weather will occur this morning ahead of a series of two storms expected to move through the forecast area this afternoon/evening and tomorrow afternoon/evening. Snow level today is forecast around 8,000' to 9,000'. Snow level is expected to remain fairly high until lowering to around 6,000' Monday afternoon/evening. Minimal amounts of high density new snow are expected today at the upper elevations from 0.2 to 0.3 inches of rain water equivalent. More significant accumulation is expected from the Monday system, especially along the Sierra Crest above 8,000'. Ridgetop winds are continuing to increase this morning. Strong winds today are expected to reach gale force late this afternoon, evening, and tomorrow. Increasing SW winds have mixed out the air temperature inversion, but remote sensors are reporting air temperatures above freezing in all areas below 9,000'. Maximum daytime air temperatures are expected to reach into the 40s today for all but the highest elevations.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 34 to 39 deg. F.
Max. temperature in the last 24 hours: 46 to 50 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 27 mph
Maximum wind gust in the last 24 hours: 48 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 76 to 113 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 skies, becoming cloudy. A chance of rain in the afternoon. Mostly cloudy skies with a chance of rain. A chance of snow after midnight. Mostly cloudy skies becoming cloudy. A chance of snow in the morning. Snow likely in the afternoon.
Temperatures: 45 to 51 deg. F. 27 to 34 deg. F. 36 to 42 deg. F.
Wind Direction: SW SW SW
Wind Speed: 25 to 35 mph with gust to 45 mph. Gusts increasing to 55 mph in the afternoon. 30 to 40 mph with gusts to 60 mph. 30 to 35 mph with gusts to 55 mph, increasing to 40 to 45 mph with gusts to 75 mph in the afternoon.
Expected snowfall: 0 in. Up to 1 in. Up to 2 in.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy skies with a chance of rain and snow in the afternoon. Mostly cloudy skies with a chance of rain in the evening. A chance of snow through the night. Mostly cloudy skies becoming cloudy. A chance of snow in the morning. Snow likely in the afternoon.
Temperatures: 42 to 48 deg. F. 25 to 32 deg. F. 32 to 38 deg. F.
Wind Direction: SW SW SW
Wind Speed: 35 to 40 mph with gusts to 55 mph, increasing to 50 to 55 mph with gusts to 85 mph in the afternoon. 50 to 60 mph with gusts to 85 mph. 55 to 60 mph with gusts to 85 mph, increasing to 65 to 70 mph with gusts to 105 mph in the afternoon.
Expected snowfall: 0 to trace in. Up to 3 in. Up to 2 in.
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