THIS AVALANCHE ADVISORY EXPIRED ON February 7, 2014 @ 7:00 am
Avalanche Advisory published on February 6, 2014 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE avalanche danger exists on slopes steeper than 35 degrees at all elevations on the NW-N-NE aspects and on near and above treeline E-SE aspects. A combination of wind slabs resting on weak snow, old persistent slabs, and loose snow sluffs represent the main avalanche problems today. Human triggered avalanches could be possible today.

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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New snow and moderate to strong southwest winds will form new wind slabs on the near and above treeline NW-N-NE-E-SE aspects today. Wind loading will also add depth and size to the small wind slabs that already existed in those places. A layer of cold, soft, and weak snow resides below these wind slabs. The combination of a weak layer underneath a wind slab will make human triggered avalanche activity possible today. Some wind slabs could reach 1 to 3 ft. in depth in heavily wind loaded areas.

Avalanche Problem 2: Persistent Slab
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In areas above 9,500 ft. on near treeline and below treeline NW-N-NE aspects, human triggered persistent slab avalanches could be possible today. Weak layers of well developed facets and depth hoar still remain buried in the snowpack in these areas. With the additional snow and wind expected today the load above these layers will increase and make them more fragile. Since there are very few areas in the forecast area with terrain above this elevation where these conditions exist, this problem remains isolated in distribution.

Avalanche Problem 3: Loose Dry
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Human triggered loose dry sluffs could occur in non-wind affected areas below 9500 ft. on near and below treeline NW-N-NE slopes where cold unconsolidated snow rests on top of a frozen rain crust. These sluffs could entrain enough snow to knock a person over or push them off course into obstacles. 

recent observations

Yesterday observations on Red Lake Peak below 9500 ft, in Deep Creek below 8500 ft, and on Freel below 9300 ft, showed up to 16 inches of soft, cold snow resting on top of a thick supportable rain crust. Below this thick refrozen layer some moist unconsolidated snow still remained in the Red Lake Peak area. Above 9300 ft on Freel and on Chickadee Ridge in the Mt. Rose backcountry the rain crust became much thinner, and dry, weak facetted snow grains remained in the bottom part of the snowpack. Data and observations from all of these locations at all elevations showed the cold soft surface snow on the NW-N-NE aspects has very little strength and that it may not support a new snow load very well. Even though some surface hoar existed on the surface in some areas yesterday, no data indicated intact buried surface hoar yesterday.

Some wind transport did occur yesterday, and some small and isolated wind slabs did exist near ridgelines in areas prone to wind loading in Deep Creek, on Red Lake Peak, and on Freel. Some sluffing also occurred on steep slopes in Deep Creek as the soft snow slid downslope on the rain crust. 

Weather and CURRENT CONDITIONS
weather summary

The first in a series of storms arrived over the region last night. So far 1-2 inches of new snow has fallen since early this morning. The southwest winds have started to increase as well. The forecast calls for another 5-10 inches of snow toady and southwest winds in the 30-40 mph range. This storm should start to taper off overnight, but snow showers could continue through Friday morning. By Friday afternoon another stronger, wetter, and warmer system should begin to impact the forecast area bringing more wind and snow. Tomorrow afternoon snow levels should begin around 4500-5000 ft. However, as this system pulls warmer air into the region, snow levels should quickly rise overnight on Friday. Keep checking in with the Reno NWS for the latest forecasts and details about these storms.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 19 to 24 deg. F.
Max. temperature in the last 24 hours: 23 to 30 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 15 to 25 mph
Maximum wind gust in the last 24 hours: 45 mph
New snowfall in the last 24 hours: 1 to 2 inches
Total snow depth: 15 to 31 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Thursday Thursday Night Friday
Weather: Snow Cloudy with snow showers decreasing overnight Cloudy with a chance of snow.
Temperatures: 28 to 34 deg. F. 16 to 21 deg. F. 28 to 35 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 20 to 30 mph with gusts to 40 mph 20 to 30 mph with gusts to 45 mph 25 to 35 mph with gusts to 55 mph
Expected snowfall: 5 to 8 in. up to 2 in. up to 5 in.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Snow Cloudy with snow showers decreasing overnight Cloudy with a chance of snow.
Temperatures: 21 to 29 deg. F. 12 to 17 deg. F. 23 to 30 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 30 to 40 mph with gusts to 50 mph increasing to 60 mph in the afternoon 25 to 30 mph with gusts to 45 mph increasing to 35 to 40 mph with gusts to 60 mph after midnight 40 to 50 mph with gusts to 75 mph
Expected snowfall: 5 to 10 in. up to 2 in. up to 5 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.