THIS AVALANCHE ADVISORY EXPIRED ON January 19, 2017 @ 6:56 am
Avalanche Advisory published on January 18, 2017 @ 6:56 am
Issued by Brandon Schwartz - Tahoe National Forest

LOW avalanche danger continues through the morning hours today. Following the onset of precipitation, MODERATE avalanche danger will exist at all elevations on slopes 35 degrees and steeper. Avalanche danger will further increasing to CONSIDERABLE danger during the evening and overnight hours at all elevations on slopes 30 degrees and steeper. Expect new wind slabs and storm slabs to form during the afternoon and overnight hours. Natural avalanches are possible tonight.

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: Wind Slab
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Little to no snow is available for wind transport near and above treeline prior to the onset of new snowfall. This avalanche problem will begin to form this afternoon following to onset of snowfall. The combination of new snow and strong to gale force SW winds will create new wind slabs mainly near and above treeline on NW-N-NE-E-SE aspects. Wind slabs are expected to remain small in size this afternoon, becoming large during the overnight hours.

Avoid areas of wind slab by avoiding slopes that accumulate blowing snow, new wind pillows, and new cornice formations.

 

Avalanche Problem 2: Storm Slab
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This avalanche problem will begin to form this afternoon following the onset of snowfall. As new snow accumulates, a slab of storm snow will be deposited on all aspects near treeline and below treeline. In some areas this slab of new snow will be deposited on top of weak near surface facet crystals. In isolated areas, this slab may deposit on top of very weak surface hoar crystals. Anyplace that these new slabs form on top of these weak snow crystals, storm slabs could be very sensitive to human triggering after just a few inches of snowfall. Expected avalanche size will start out small this afternoon, becoming large during the overnight hours.

Early in the storm cycle, snow surface cracking will be the most likely indication that storm slabs exist in the area of interest. As storm slabs become thicker, signs of instability such as snowpack collapse and whumpfing sounds will become possible. Avoid slopes steeper than 30 degrees in areas where signs of unstable storm slabs are present.

 

Avalanche Problem 3: Loose Wet
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Any areas of rain on snow today may create small wet loose avalanches. This is most likely to occur in areas below 7,200' on W-NW-N-NE-E aspects in locations where the snow surface has yet to undergo any melting.

 

recent observations

Recent observations from around the forecast area indicate that in some locations weak snow crystal types exist at the old snow surface that could lead to instability at the old/new snow interface. The weak crystal types of concern are near surface facets and surface hoar crystals that exist near treeline and below treeline on open slopes that are typically wind protected and shaded. The layers deeper in the snowpack appear in good condition to handle new snow loading.

Weather and CURRENT CONDITIONS
weather summary

The first in a series of storm systems to impact the region will move into the forecast area today. Ridgetop winds out of the SW are increasing ahead of the first system. Ridgetop gusts to 60 mph this morning will increase to 100 mph this afternoon. Light precipitation is expected to begin sometime in the 10 am to 2 pm time frame. Snow level is forecast to begin around 6,700' to 7,200' and fall to below 6,000' by 5 pm this evening. Snowfall intensity is expected to increase after 4 pm and continue through the overnight hours. Winds and precipitation are forecast to decrease during the day tomorrow before the next storm system arrives tomorrow night.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 24 to 30 deg. F.
Max. temperature in the last 24 hours: 38 to 49 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 39 mph
Maximum wind gust in the last 24 hours: 60 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 75 to 103 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Wednesday Wednesday Night Thursday
Weather: Cloudy skies with a chance of rain and snow. Cloudy skies with snow. Cloudy skies with snow likely in the morning. A chance of snow in the afternoon.
Temperatures: 34 to 39 deg. F. 20 to 25 deg. F. 26 to 31 deg. F.
Wind Direction: SW SW SW
Wind Speed: 20 to 30 mph. Gusts to 50 mph increasing to 70 mph in the afternoon. 20 to 35 mph with gusts to 70 mph. 15 to 25 mph. Gusts to 50 mph decreasing to 35 mph in afternoon.
Expected snowfall: Up to 3 in. 5 to 10 in. 1 to 3 in.
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Cloudy skies with a chance of snow. Cloudy skies with snow. Cloudy skies with snow in the morning. Snow likely in the afternoon.
Temperatures: 31 to 37 deg. F. 18 to 23 deg. F. 23 to 29 deg. F.
Wind Direction: SW SW SW
Wind Speed: 25 to 40 mph with gusts to 80 mph, increasing to 30 to 50 mph with gusts to 100 mph in the afternoon. 35 to 55 mph with gusts to 115 mph. 30 to 40 mph with gusts to 80 mph, decreasing to 15 to 25 mph with gusts to 50 mph in the afternoon.
Expected snowfall: Up to 3 in. 5 to 11 in. 1 to 4 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