THIS AVALANCHE ADVISORY EXPIRED ON December 20, 2014 @ 6:58 am
Avalanche Advisory published on December 19, 2014 @ 6:58 am
Issued by Brandon Schwartz - Tahoe National Forest

Areas of MODERATE avalanche danger are expected to form today both above and below treeline on NW-N-NE-E-SE aspects on slopes 32 degrees and steeper. For all other areas, avalanche danger is LOW. Expect wind slabs near and above treeline and potential pockets of storm slab below treeline. The areas of greatest avalanche danger will exist north of Hwy 50.

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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A new round of wind slab formation is expected to occur today as new snow and wind combine to build fresh slabs in wind loaded areas. The likelihood of human triggered avalanches will increase as the day progresses in near and above treeline terrain on NW-N-NE-E-SE aspects. The largest wind slabs are expected to form north of Hwy 50 along the Sierra Crest.

Avalanche Problem 2: Storm Slab
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In wind protected open areas near and below treeline, the potential exists for areas of surface hoar to become a buried weak layer today. Shallow human triggered storm slab avalanches could occur in open wind protected areas where the upper end of forecast new snow amounts are reached. Surface hoar will need to have survived destruction by increasing SE to SW winds last night and this morning for this to become an avalanche problem.

recent observations

Observations made yesterday in the Carson Pass area on both Red Lake Peak and near Frog Lake Cliffs revealed that difficult to trigger wind slabs remained present in the area. Evidence of instability was limited to snowpit tests on NW and NE aspects. Variable test results were noted on the widespread weak layer of lower density recent storm snow that exists at the base of the surface wind slab. Additional observations made yesterday in the Mount Rose area revealed small, isolated, and difficult to trigger wind slabs on NW-N-NE aspects. A public submitted observation indicated improving snowpack stability on the north side of Castle Peak (Donner Summit area). Sizeable areas of 1 to 10 mm surface hoar have been noted around the forecast area over the past two days. The potential exists for this surface hoar to become a buried weak layer today.

Weather and CURRENT CONDITIONS
weather summary

A couple of weather systems passing mainly to the north of the forecast area will bring snowfall today into tomorrow. New snow amounts of 2 to potentially 8 inches are expected over the next 24 hours, with the greatest accumulations along the Sierra Crest north of Hwy 50. Light snow showers this morning are expected to increase in intensity this afternoon through this evening. Remote sensors are reporting air temperatures this morning at 8,000' to 9,000' in the 20s. Maximum daytime air temperatures are forecast to reach the mid 20s to mid 30s today for areas above 7,000'. Ridgetop winds shifted from southeast to southwest overnight and have become strong to gale force in speed. Remote sensors reported ridgetop gusts of 63 to 87 mph early this morning.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 20 to 29 deg. F.
Max. temperature in the last 24 hours: 28 to 31 deg. F.
Average wind direction during the last 24 hours: Southeast shifting to southwest
Average wind speed during the last 24 hours: 25 mph
Maximum wind gust in the last 24 hours: 63 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 25 to 38 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Cloudy skies with snow showers, potentially heavy at times north of Hwy 50. Mostly cloudy skies with a chance of snow. Mostly cloudy skies with a chance of snow.
Temperatures: 30 to 35 deg. F. 24 to 29 deg. F. 32 to 37 deg. F.
Wind Direction: SW SW SW
Wind Speed: 10 to 20 mph with gusts to 30 mph. 10 to 15 mph with gusts to 25 mph. 10 to 15 mph with gusts to 25 mph.
Expected snowfall: Trace to 4 in. Trace to 2 in. Trace to 1 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Cloudy skies with snow showers, potentially heavy at times north of Hwy 50. Mostly cloudy skies with a chance of snow. Mostly cloudy skies with a chance of snow.
Temperatures: 23 to 30 deg. F. 19 to 25 deg. F. 25 to 32 deg. F.
Wind Direction: SW SW SW to W
Wind Speed: 20 to 35 mph with gusts to 50 mph. 15 to 25 mph with gusts to 35 mph. 15 to 25 mph with gusts to 35 mph, increasing to 25 to 30 mph with gusts to 45 mph in the afternoon.
Expected snowfall: Trace to 5 in. Trace to 2 in. Trace to 1 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.