THIS AVALANCHE ADVISORY EXPIRED ON February 13, 2014 @ 7:00 am
Avalanche Advisory published on February 12, 2014 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE avalanche danger exists on slopes 35 degrees and steeper on all aspects in near and above treeline terrain due to new wind slabs, the formation of loose wet snow, and unlikely but not impossible deep persistent slabs. MODERATE avalanche danger also exists below treeline on slopes 35 degrees and steeper on the SE-S-SW-W aspects due to the formation of loose wet snow.

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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Strong southwest winds combined with some snow still available for transport on the upper elevation windward aspects, means that new wind slabs could form on leeward slopes today. These wind slabs should remain smaller than those that formed during the storm, but human triggering of them will be possible today. The wind loaded NW-N-NE-E-SE aspects in near and above treeline terrain will hold the most fragile wind slabs. Even though it is unlikely it is not impossible that failure of these wind slabs could add enough weight to the snowpack to cause the resulting avalanches to step down to deeper weaknesses in the snowpack.

Avalanche Problem 2: Loose Wet
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Warmer overnight temperatures, daytime warming, and sunshine could cause enough melting in the upper snowpack for some wet snow instabilities to form again today on the E-SE-S-SW-W aspects below 8500 ft. These should remain limited to surface instabilities like roller balls, pin wheels, and wet loose avalanches. Wet slabs should remain unlikely, but not impossible today.

Avalanche Problem 3: Persistent Slab
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Weak layers of well developed facets and depth hoar remain buried deep in the snowpack on near and below treeline NW-N-NE aspects above 9,000 ft. The strong thick layer of new snow above these weak layers has made breaking these weak layers difficult and deep persistent slab avalanche activity has become unlikely. However, it is not impossible for the right trigger in the right place to still release one of these slabs. Areas where a shallower snowpack exists (like where the whumphing occurred on Tamarack yesterday) or where trigger points like rocks are closer to the surface could allow humans to still trigger these slides. Since near and below treeline areas above 9,000 ft. only represent a small portion of the forecast area this problem remains isolated in distribution.

recent observations

Observations from near Round Top on Carson Pass, Talking Mountain on Echo Summit, and Tamarack Peak in the Mt. Rose area all showed a thick layer of storm snow ranging from 3 to 6 ft in depth. The storm snow in all three of these locations showed signs of continued settlement and consolidation. On Talking Mountain and near Round Top some less dense layers still remained within the storm snow in the top 3 to 4 ft of the snowpack, but data and observations did not reveal any signs of instability associated with those storm snow weakness. As the winds picked up yesterday they started transporting snow at the upper elevations and adding more wind loading to leeward slopes on Talking Mountain and in the Round Top area.

In all three of these areas yesterday, weak snow still exists at the bottom of the snowpack at the upper elevations. On Round Top, on Talking Mountain, and in most places on Tamarack data and observations indicated that while this weakness remains, it would be very difficult to trigger. However, human triggered whumphing did occur in one spot on Tamarack Peak where a shallower (2-3ft in depth) snowpack existed. 

Some wet loose avalanche activity did occur yesterday on the SE-S aspect of Jake's Peak, and some skier triggered wet loose sluffs occurred on steep, sun-exposed, S facing test slopes between 7600 and 8200 ft. on Talking Mountain.

Weather and CURRENT CONDITIONS
weather summary

A strong storm moving into the Pacific Northwest has brought increased west and southwest winds and warmer air to the forecast area. Winds should remain in the 45 to 60 mph range with gusts between 80 and 90 mph though tomorrow afternoon. Air temperatures should climb into the upper 30's and even into the upper 40's below 8000 ft. today and into the low to upper 40's tomorrow. The forecast also calls for increased cloud cover due to this storm; however, most of the precipitation should stay north of the region. A slight chance for a small amount of rain and/or snow does exist for the northern part of the forecast area tonight and tomorrow.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 26 to 37 deg. F.
Max. temperature in the last 24 hours: 36 to 43 deg. F.
Average wind direction during the last 24 hours: West and southwest
Average wind speed during the last 24 hours: Before midnight: 10 to 20 mph | Since midnight: 40 to50 mph
Maximum wind gust in the last 24 hours: 75 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 45 to 56 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy Mostly cloudy with a slight chance of snow Mostly cloudy with a slight chance of rain
Temperatures: 38 to 48 deg. F. 26 to 33 deg. F. 42 to 49 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 15 to 30 mph with gusts to 50 mph 20 to 30 mph with gusts to 40 mph 15 to 25 mph with gusts to 40 mph
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy Mostly cloudy with a slight chance of snow Mostly cloudy with a slight chance of rain and snow
Temperatures: 32 to 38 deg. F. 26 to 32 deg. F. 32 to 42 deg. F.
Wind Direction: West Southwest Southwest
Wind Speed: 45 to 60 mph with gusts to 85 mph 50 to 70 mph with gusts to 90 mph 45 to 55 mph with gusts to 80 mph
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.