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 January 21, 2008 7:00 AM

Near and above treeline, areas of MODERATE avalanche danger exist on wind loaded N-NE-E aspects, 35 degrees and steeper. Below treeline, areas of MODERATE avalanche danger exist in open areas 37 degrees and steeper where loose snow avalanche activity is expected.

Light to moderate snowfall began late yesterday afternoon. Snowfall ceased for several hours overnight, then began again this morning. Based on data from remote sensors and the Alpine Meadows snow study plot, new snow accumulation varies widely from one location to another within the forecast area. New snow amounts of 2 to 6 inches with 5% density have been reported along the Sierra Crest, while 2 to 3 inches of new snow has been reported in the Mount Rose area and along the Carson Range south to Luther Pass. Ridgetop winds decreased during the day yesterday and remain moderate from the west southwest this morning. Wind transport of snow is expected to continue through the day today.

This morning, snowpack instability will be found near and above treeline in wind loaded areas where the greatest new snow accumulations have occurred. As the day progresses, newly formed slabs will become more widespread in wind loaded areas. Moderate ridgetop winds will load snow high in avalanche start zones on N-NE-E aspects. As snowfall continues, some isolated areas of small unstable slabs are possible above treeline on cross loaded NW and SE aspect gully features. Below treeline, human triggered loose snow avalanche activity is expected in open areas 37 degrees and steeper where several inches of low density new snow sit on top of a hard old snow surface.

Yesterday at the onset of snowfall, graupel was observed as the new snow crystal form along the Sierra Crest north of I-80. The extent of area affected by this event is unknown at this time. Areas where graupel is found at the old/new snow interface may show poor bonding to the old snow surface today.

Some very small and very isolated patches of surface hoar crystals linger on north aspect micro features. These patches have been buried under new snow, but are not expected to play a significant role in snowpack instability over the next several days due to their very isolated distribution. An isolated collapse and whumpf sound are all that is expected to occur. With the limited size and isolated island like presence of the surface hoar patches, significant fracture propagation on this weak layer is unlikely.

Layers within the existing deeper snowpack are in good condition to handle the amount of new snow loading that is expected to occur over the next several days, despite the presence of near surface faceted crystals in many locations. Avalanche activity that occurs today is expected to be human triggered and fail at the interface between the old and new snow.

The bottom line: Near and above treeline, areas of MODERATE avalanche danger exist on wind loaded N-NE-E aspects, 35 degrees and steeper. Below treeline, areas of MODERATE avalanche danger exist in open areas 37 degrees and steeper where loose snow avalanche activity is expected.
Please send us your snow, weather, and avalanche observations by clicking the submit observations link on our contact page.

Brandon Schwartz, Avalanche Forecaster

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: 20 deg. F
Average wind direction at Sierra Crest past 24 hours: West southwest
Average wind speed at Sierra Crest past 24 hours: 38 mph
Maximum wind gust at Sierra Crest past 24 hours: 75 mph
New snow fall at 8,200 feet past 24 hours: 2 to 6 inches
Total snow depth at 8,200 feet: 60 inches

Mountain Weather Forecast For Today:
Cloudy skies with scattered snow showers in the morning. Snow showers increasing in the afternoon.
Temperature forecast for 8,000 to 9,000 feet: 15 to 21 deg. F
Ridgetop winds forecast for the Sierra Crest: Southwest at 15 to 25 mph with gusts to 45 mph.
Snowfall expected in the next 24 hours: 5 to 9 inches

2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, cloudy skies with isolated snow showers in the morning. Increasing snow showers in the afternoon. Snow accumulation 2 to 5 inches. Daytime highs around 22 deg. F. Southwest winds at 10 to 15 mph with gusts to 35 mph.

Tonight, cloudy skies with snow showers in the evening, then scattered snow showers after midnight. Snow accumulation up to 3 inches. Overnight lows around 10 deg. F. Southeast winds at 10 mph with gusts to 25 mph in the evening.

For Tuesday, cloudy skies with scattered snow showers. Snow accumulation up to 2 inches. Daytime highs around 23 deg. F. East winds at 10 mph.

Above 8000 Feet:
Today, cloudy skies with isolated snow showers in the morning. Increasing snow showers in the afternoon. Snow accumulation 3 to 6 inches. Daytime highs 15 to 21 deg. F. Southwest winds at 10 to 15 mph with gusts to 45 mph.

Tonight, cloudy skies with snow showers in the evening, then scattered snow showers after midnight. Snow accumulation 2 to 3 inches. Overnight lows around 8 deg. F. South winds at 10 mph shifting to the east after midnight. Gusts up to 30 mph.

For Tuesday, cloudy skies with scattered snow showers. Snow accumulation up to 3 inches. Daytime highs around 18 deg. F. East winds at 10 to 15 mph, with gusts to 25 mph.

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.