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 advisory was posted on December 17, 2007 7:20 AM
Click here for a detailed map of the SAC forecast area

Low avalanche danger
Today's Advisory:
Natural and human triggered avalanche activity in not expected today. Shallow buried objects such as rocks, down trees, and stumps remain the major threat to backcountry travelers.

The first in a series storm systems reached the forecast area last night. Up to 6 inches of snow fell last night north of Lake Tahoe along the Sierra Crest. South of Highway 50 and in the Mount Rose area snow accumulations only reached about an inch. Snow should continue through today with another 2 to 4 inches accumulating. Another storm system should reach the forecast area tonight and snowfall intensity should increase overnight and through tomorrow. 4 to 8 inches of additional accumulation is predicted for the forecast area tonight and another 10 to 18 inches during the day tomorrow. The southwest winds accompanying this series of storms should continue to buffet the forecast area through most of this week.

These southwest winds will be more than enough to transport snow. The open slopes near and above treeline on N-NE-E aspects and gully features should experience the most wind loading and should be the first areas to fill in. As the snow accumulates on these wind loaded slopes, wind slabs will start to form. These slabs should start out as small, disconnected pillow drifts. However, if the snow continues to accumulate and the winds continue to blow as forecast this week, more extensive wind slabs will form.

In the areas that still held snow cover from the December 6-7th storm, the combination of a shallow snowpack and consistently cold temperatures have caused the snow grains to weaken. In those areas the snowpack consists of a mix of decomposing new snow and faceted grains (weak, sugary snow). This stratigraphy is overlain by a variety of thin breakable crusts in many areas. These weak layers in the snowpack could fail as the snow piles up on top of them this week.

Avalanche activity is unlikely today. The biggest hazard is still going to be a shallow snowpack that barely covers many rocks, logs, and stumps. Crashing into these objects could easily ruin the winter. The avalanche hazard will increase as more snow falls and as more wind slabs form this week. Remember to stay observant as you travel, look for indications of the current snowpack stability such as recent avalanche activity, wind loading, collapse, audible whumpfing sounds, shooting cracks, and/or test slope failure. Any of these signs are indications of current snowpack instability.

The bottom line: The avalanche danger is LOW today at all elevations and aspects. Natural and human triggered avalanche activity is unlikely today. Collision with shallow buried objects such as rocks, down trees, and stumps remains the major threat to backcountry travelers

Andy Anderson, Avalanche Forecaster

Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet): 18 deg. F
Max. temperature at Sierra Crest past 24 hours: 26 deg. F
Average wind direction at Sierra Crest past 24 hours: Southwest
Average wind speed at Sierra Crest past 24 hours: 45 mph
Maximum wind gust at Sierra Crest past 24 hours: 92 mph
New snow fall at 8,200 feet past 24 hours: 6 inches
Total snow depth at 8,200 feet: 19 inches
Mountain Weather Forecast For Today:
Cloudy with snow showers. Accumulation of 2-4 inches.
Temperature forecast for 8,000 to 9,000 feet: 24 to 30 deg. F.
Ridgetop winds forecast for the Sierra Crest: Southwest at 30 to 40 mph with gusts to 70 mph.
Snowfall expected in the next 24 hours: 5-10 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today snow showers with up to 2 inches of accumulation. Daytime highs 30 to 36 deg. F. Winds should be out of the southwest at 15 to 20 mph with gusts to 30 mph.

Tonight 3 to 6 inches of snow with overnight lows around 28 deg. F. Winds out of the southwest at 15 to 25 mph with gusts to 40 mph expected.

For Tuesday 7 to 14 inches of snow with daytime highs around 32 deg. F. Winds out of the southwest at 20 to 30 mph with gusts to 45 mph expected.

Above 8000 Feet:
Today snow showers with 2 to 4 inches of accumulation. Daytime highs 24 to 30 deg. F. Winds should be out of the southwest at 30 to 40 mph with gusts to 70 mph.

Tonight 4 to 8 inches of snow with overnight lows around 24 deg. F. Winds out of the southwest at 25 to 35 mph with gusts to 80 mph expected.

For Tuesday 10 to 18 inches of snow with daytime highs around 28 to 30 deg. F. Winds out of the southwest at 30 to 50 mph with gusts to 100 mph expected.

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.