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.


This Avalanche Advisory was published on December 15, 2008:


December 15, 2008 at 1:00 am

Forecast Discussion:


This advisory was posted on December 15, 2008 6:58 AM

A map of the SAC forecast area is available on our home page.

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Today's Advisory:
Near and above treeline, avalanche danger is CONSIDERABLE on NW-N-NE-E-SE aspects, 35 degrees and steeper. Below treeline, avalanche danger is MODERATE on NW-N-NE aspects above 7,500' that are 32 degrees and steeper.

The current storm system that is affecting the forecast area is expected to continue into tomorrow. Mountain top air temperatures are expected to remain in the single digits to low teens today. Ridgetop winds have increased overnight and are expected to remain moderate to strong out of the west southwest. Storm totals thus far at 8,000' are running 22 to 25 inches across the forecast area.

Yesterday, a small human triggered avalanche was reported on Slide Mtn (Mount Rose area). The avalanche was triggered by an individual on foot traveling through a natural, undisturbed snowpack. The avalanche rated class D1, occurred below treeline on a 35 degree, north aspect, at approximately 9,200'. The snowpack failed on an old snow layer of faceted snow crystals. Observations on Castle Peak (Donner Summit area) showed significant wind loading in lee areas. Wind loaded avalanche start zones were filled in with 16 to 40 inches of new snow. Several weakness were observed within the wind loaded snow, but stability tests indicated that fracture propagation was unlikely in that area around mid day yesterday. Greater snowpack instability is expected today with the addition of last night's snowfall.

Avalanche concern number one: An additional 10 to 15 inches of new snow fell last night. Ridgetop winds have continued to wind load and create slabs in avalanche start zones, mainly on NW-N-NE-E-SE aspects. Natural and human triggered avalanches that are large enough to bury a person are possible today.

Avalanche concern number two: Near and below treeline new snow sits on top of a weak layer of well developed faceted snow crystals in some areas. This weak layer is the remnants of the 11/26 snowfall that has now become a buried weak layer at the bottom of the new snow. This weak layer exists above 7,500' on east wind protected NW-N-NE aspects in near and below treeline areas. Unstable snow is expected in areas where this faceted snow layer exists as it will handle new snow loading poorly, even on lower angle slopes.

The bottom line:

Near and above treeline, avalanche danger is CONSIDERABLE on NW-N-NE-E-SE aspects, 35 degrees and steeper. Below treeline, avalanche danger is MODERATE on NW-N-NE aspects above 7,500' that are 32 degrees and steeper.

Please share your backcountry observations with us, especially if you see or trigger an avalanche. To report an observation click here.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet): 11 deg. F.
Max. temperature at Sierra Crest past 24 hours: 13 deg. F.
Average wind direction at Sierra Crest past 24 hours: West Southwest
Average wind speed at Sierra Crest past 24 hours: 33 mph
Maximum wind gust at Sierra Crest past 24 hours: 77 mph
New snowfall at 8,200 feet past 24 hours: 10 to 15 inches
Total snow depth at 8,200 feet: 15 to 35 inches

Mountain Weather Forecast For Today:
Cloudy with periods of snow, heavy snowfall at times.
Temperature forecast for 8,000 to 9,000 feet: 8 to 13 deg. F
Ridgetop winds forecast for the Sierra Crest: Southwest winds at 25 to 40 mph with gusts to 60 mph.
Snowfall expected in the next 24 hours: 12 to 24 inches

2 Day Mountain Weather Forecast:

7000 to 8000 Feet:

Today, cloudy with snow showers, heavy snowfall at times. Snow accumulation 6 to 12 inches. Daytime highs 13 to 21 deg. F. Southwest winds at 15 to 20 mph with gusts to 40 mph.

Tonight, cloudy with continued snow showers. Snow accumulation 6 to 12 inches. Overnight lows 2 to 8 deg. F. Southwest winds at 10 to 20 mph with gusts to 30 mph.

Tomorrow, snow showers likely. Snow accumulation 2 to 5 inches. Daytime highs 10 to 17 deg. F. Southwest winds at 10 to 15 mph, becoming variable around 10 mph in the afternoon.

Above 8000 Feet:

Today, cloudy with snow showers, heavy snowfall at times. Snow accumulation 6 to 12 inches. Daytime highs 8 to 13 deg. F. Southwest winds at 20 to 40 mph with gusts to 60 mph.

Tonight, cloudy with continued snow showers. Snow accumulation 6 to 12 inches. Overnight lows -4 to 3 deg. F. Southwest winds at 20 to 35 mph with gusts to 50 mph.
Tomorrow, snow showers likely. Snow accumulation 2 to 5 inches. Daytime highs 5 to 10 deg. F. Southwest winds at 10 to 15 mph with gusts to 30 mph, becoming variable around 10 mph in the afternoon.


The bottom line:


Andy Anderson - Avalanche Forecaster, Tahoe National Forest


Weather Observations from along the Sierra Crest between 8200 ft and 8800 ft:

0600 temperature: deg. F.
Max. temperature in the last 24 hours: deg. F.
Average wind direction during the last 24 hours:
Average wind speed during the last 24 hours: mph
Maximum wind gust in the last 24 hours: mph
New snowfall in the last 24 hours: O inches
Total snow depth: inches

Two-Day Mountain Weather Forecast - Produced in partnership with the Reno NWS

For 7000-8000 ft:

  Monday: Monday Night: Tuesday:
Weather:
Temperatures: deg. F. deg. F. deg. F.
Wind direction:
Wind speed:
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Monday: Monday Night: Tuesday:
Weather:
Temperatures: deg. F. deg. F. deg. F.
Wind direction:
Wind speed:
Expected snowfall: O in. O in. O in.