THIS AVALANCHE ADVISORY EXPIRED ON January 20, 2016 @ 6:58 am
Avalanche Advisory published on January 19, 2016 @ 6:58 am
Issued by Steve Reynaud - Tahoe National Forest

Moderate avalanche danger exists on all aspects and elevations through the morning hours.  As the incoming storm intensifies by mid day, avalanche danger will rise to considerableWind slabs will develop on NW-N-NE-E-SE aspects near and above treeline and persistent slabs will be possible on N-NE-E aspects near treeline and below treeline on slopes 32 degrees or steeper.  Natural avalanche activity will become possible this afternoon with human triggered avalanche activity possible to likely all day.  

 

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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New wind slabs will begin forming this morning as our next storm approaches with SW gale force winds gusting over 100mph along the Sierra Crest.  These wind slabs could exist on NW-N-NE-E-SE aspects near and above treeline.  Look for areas of blowing snow, cornice formations, wind pillows and snow surface clues as to where these wind slabs may exist.

Avalanche Problem 2: Persistent Slab
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Persistent weak layers of buried surface hoar exist 1-3.5' deep below the snow surface.  These weak layers exist on some slopes throughout the forecast area on N-NE-E aspects near and below treeline and potentially in isolated areas on NW and SE aspectsAvalanche activity has continued to occur on these weak layers over the last 2 weeks.  Many slopes have already avalanched, or the buried surface hoar has been collapsed or compressed and has gained strength.  In other areas, snowpack tests show that this buried surface hoar layer is still reactive.

This persistent weak layer will exist in open areas near and below treeline.  The recent rain and snow is adding weight and additional stress to this layerAvalanches associated with this buried surface hoar layer could be large, destructive and have severe consequences.  Remote triggering and large propagation continues to be possible. 

recent observations

Observations from Silver Peak (Pole Creek area) revealed a past avalanche that was thought to have occurred either Saturday or Sunday, potentially from a rain event.  This avalanche failed on the buried surface hoar layer and had an average slope angle of 30 degrees with a starting zone of 34 degrees.  Multiple snowpack tests showed that the buried surface hoar was still reactive in this area and that propagation continues to be possible.  A rain crust existed up to at least 8000' with 4-6'' of new storm snow on top.  Warming temperatures made for sticky snow conditions below 7000' and some minor roller ball activity on solar aspects.  There were no signs of instabilities associated with the wind slab or storm slab avalanche problems.

Observations from Blue Lakes (Carson Pass area) showed no signs of buried surface hoar in the area and no signs of any avalanche instabilities.  There was some concern of a developing future weakness associated with the recent rain crust.

Weather and CURRENT CONDITIONS
weather summary

A fast moving storm will bring another round of rain and high elevation snow to our area today.  Up to 6'' of heavy snow is forecasted above 8000' with SW winds gusting 80 to 100mph along the upper elevations.  Snow levels should rise throughout the day topping out near 6500-7000'.  We should see a break in the storm activity for Wednesday and Thursday.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 21 to 26 deg. F.
Max. temperature in the last 24 hours: 32 deg. F.
Average wind direction during the last 24 hours: SW to S
Average wind speed during the last 24 hours: 30 to 40 mph
Maximum wind gust in the last 24 hours: 67 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 58 to 63 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Cloudy. Snow Mostly cloudy. Snow showers in the evening. Partly cloudy then becoming mostly cloudy.
Temperatures: 30 to 37 deg. F. 21 to 27 deg. F. 37 to 42 deg. F.
Wind Direction: SW SW SW
Wind Speed: 25 to 40mph with gusts to 60mph. 25 to 40mph with gusts to 60mph decreasing West 15 to 25mph with gusts to 40mph. 10 to 15mph with gusts to 35mph in the morning.
Expected snowfall: 3 to 5 in. Up to 1 in. 0 in.
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Cloudy. Snow. Mostly cloudy. Snow showers in the evening. Partly cloudy then becoming mostly cloudy.
Temperatures: 26 to 31 deg. F. 20 to 25 deg. F. 32 to 37 deg. F.
Wind Direction: SW SW to W W
Wind Speed: 50 to 70mph with gusts to 80 to 100mph. 50 to 70mph with gusts up to 100mph then 35 to 55mph with gusts to 70mph after midnight. 20 to 40mph with gusts to 60mph decreasing to 15 to 25mph with gusts to 40mph.
Expected snowfall: 4 to 6 in. Up to 1 in. 0 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.