THIS AVALANCHE ADVISORY EXPIRED ON January 26, 2016 @ 6:56 am
Avalanche Advisory published on January 25, 2016 @ 6:56 am
Issued by Brandon Schwartz - Tahoe National Forest

MODERATE avalanche danger is expected today above treeline on SE-S-SW-W-NW aspects on slopes 35 degrees and steeper in areas where new wind slabs form this morning. For all other areas, LOW avalanche danger exists. Normal caution is advised. Very isolated deep persistent slab avalanches are unlikely but not impossible in open near treeline and below treeline areas on N-NE-E aspects on slopes 32 degrees and steeper.

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

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.
    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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As NE winds increase this morning, redistribution of snow on the ground is expected in above treeline areas. Visible blowing snow, wind loading, and new wind slab formation is expected today above treeline on SE-S-SW-W-NW aspects. New wind slab size is expected to be fairly small, but could reach sufficient size to bury or injure a person if avalanche activity were to occur in the most efficiently wind loaded areas. Use clues such as blowing snow, new cornice formation, wind pillows, and snow surface texture to identify suspect slopes.

Avalanche Problem 2: Deep Slab
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Deep persistent slabs have become an unlikely but not impossible avalanche problem. Areas where weak buried surface hoar layers exist 1.5 to 4.5 feet deep in the snowpack and remain in an unstable, reactive state are becoming increasingly isolated. A widespread persistent slab avalanche cycle occurred Jan 5 through 19 as these weak layers collapsed. As time has passed, distribution of these problematic weak layers has been changing. In some areas, avalanche activity has cleaned them out. In some areas they have already collapsed or been compressed and are no longer reactive. In other areas the buried surface hoar crystals are rounding and gaining strength. However, in some areas snowpit data continues to point to ongoing instability.

Even though avalanche occurrence is unlikely, consequences remain high. Due to the depth of the weak layer and density of the snow above, any deep persistent slab avalanches that do occur could be large, destructive, and difficult to survive. Open areas near treeline and below treeline on N-NE-E aspects is where this avalanche problem is found, not up near the ridgetops in the traditional avalanche start zones. This is the type of avalanche problem where a slope could avalanche after it has already been traveled by numerous individuals. For more info on managing deep persistent slabs, see the Avalanche Problems Toolbox.

recent observations

Observations were made and received yesterday from Incline Lake Peak and Mt. Baldy (Mount Rose area), Silver Peak (Pole Creek area), Mt. Tallac (Desolation Wilderness area), and Trimmer Peak (Luther Pass area). Along the ridgelines, wind slabs that had formed Thursday/Thursday night on N-NE-E aspects appeared to have gained strength. Minimal signs of instability were observed as minor skier triggered cracking in isolated areas.

On Silver Peak, snowpit data was collected at the site of one of the most recent persistent slab avalanches known to have occurred in mid elevation terrain. This was compared to post avalanche snowpit data collected one week ago that had indicated ongoing instability on buried surface hoar. Yesterday's data found no trace of the previously problematic weak layer that existed at that location previously. On Mt. Tallac and on Trimmer Peak, snowpit data targeting the deep persistent slab problem had a few of the test results point towards some potential for ongoing instability. Several buried surface hoar layers were reported as identifiable in the snowpit on Mt. Tallac.

Weather and CURRENT CONDITIONS
weather summary

High pressure is building over the forecast area. Cloud cover is decreasing this morning with sunny skies expected. Ridgetop winds shifted to the ENE last night in response to the building high pressure and are currently light in speed. Wind speeds are expected to increase to moderate to strong after sunrise this morning. Air temperature inversion conditions are expected to form tonight, trapping colder air on the valley floors. Maximum daytime air temperatures are forecast to warm for all elevations through Wednesday.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 22 to 26 deg. F.
Max. temperature in the last 24 hours: 25 to 32 deg. F.
Average wind direction during the last 24 hours: SW shifting to ENE at 2am.
Average wind speed during the last 24 hours: SW 19 mph | ENE 11 mph
Maximum wind gust in the last 24 hours: SW 27 mph | ENE 19 mph
New snowfall in the last 24 hours: 0 to trace inches
Total snow depth: 74 to 83 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy skies, becoming sunny. Clear skies. Sunny skies, becoming partly cloudy.
Temperatures: 29 to 36 deg. F. 18 to 26 deg. F. 35 to 42 deg. F.
Wind Direction: NE SE Variable
Wind Speed: 15 to 20 mph with gusts to 30 mph. 10 to 15 mph. Light winds
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy skies, becoming sunny. Clear skies. Sunny skies, becoming partly cloudy.
Temperatures: 26 to 33 deg. F. 16 to 23 deg. F. 33 to 40 deg. F.
Wind Direction: NE E E
Wind Speed: 30 to 35 mph with gusts to 50 mph, decreasing to 20 to 25 mph with gusts to 40 mph in the afternoon. 15 to 20 mph with gusts to 30 mph. 10 to 15 mph in the morning, becoming light.
Expected snowfall: 0 in. 0 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.