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 Wednesday, February 7th, 2007 at 6:57 am

The bottom line: This morning, avalanche danger is LOW for all elevations and aspects. Avalanche danger is expected to increase to MODERATE this afternoon above 8,000' on wind loaded N-NE-E aspects 32 degrees and steeper. Avalanche danger is expected to continue to rise overnight into Thursday.

At this time, we have not raised enough money to meet our operating budget for this year. If you use this service with any regularity and would like to continue to do so, please show your support for the Sierra Avalanche Center. You may make a tax deductible donation directly to us via Paypal or by sending a check to our address listed above, c/o the Truckee Ranger Station. For more details on SAC's current financial situation, click here. The financial graph will be updated as soon as the final numbers are calculated from the recent fundraising event at Homewood Ski Area. The financial support already received this winter from a variety of users is greatly appreciated.

The high pressure that dominated the forecast area for the past month has moved to northern Alaska. This is allowing moisture to stream unblocked through the middle latitudes and into Central California. Rain and snow is expected to begin by late morning and continue through the overnight hours. Wet weather and fluctuating snow levels are expected to continue into next week. Ridgetop winds over the Sierra Crest will increase as the day progresses. Skies will become increasingly cloudy through the morning hours.

A highly variable snowpack exists throughout the forecast area. Some areas along the Sierra Crest, especially sun exposed aspects below 8,000' and other low elevation areas have gained significant snowpack strength over the past few days. Other areas along the Sierra Crest, such as shaded northerly aspects in the 7,500'-8,500' range, are still showing weakness within faceted layers and at crust interfaces. These areas have only developed thin melt-freeze surface crusts over the past several days. Faceted snow is still highly visible near the snow surface and deeper within the existing snowpack in these areas. Wind protected areas above 8,500' are showing a deeper and stronger snowpack. Wind scoured areas above 8,500' along ridgelines hold a shallow snowpack with moderately weak faceted snow still evident. Faceted snow of moderate weakness is evident in most snow covered areas in the Mount Rose zone, especially on northerly aspects above 8,500'.

As the first of a series of storm systems moves into the forecast area, snow levels are expected to begin around 6,500' late this morning. Snowfall amounts of 2-4 inches during the day today and an additional 3-6 inches overnight will fall on high density wind slab and/or melt-freeze crust in avalanche start zones. Ridgetop winds gusting to 80 mph will cause wind loading and increase new snow deposition on N-NE-E aspects in near and above treeline areas above 8,000'. The possibility of human triggered slab avalanches 4-8 inches deep, occurring at the interface of the old and new snow, is expected to begin this afternoon. Expected snowfall during the next 24 hours will be insufficient to create instability deeper within the existing snowpack. This will become an increasing avalanche concern over the next few days as new snow accumulations exceed 1-2 feet.

The snowpack in some areas is in good condition to handle new snow loading. In other areas it is not. The existing snowpack within the forecast area is very different than the snowpack observed during February of recent winters. Significant avalanche activity is possible during the coming days. Backcountry travelers must prepare for the possibility of snowpack instability that has not been observed in this area in during the past few winters. Very careful observation and route selection will be necessary.

The bottom line: This morning, avalanche danger is LOW for all elevations and aspects. Avalanche danger is expected to increase to MODERATE this afternoon above 8,000' on wind loaded N-NE-E aspects 32 degrees and steeper. Avalanche danger is expected to continue to rise overnight into Thursday.

With the return of precipitation to the forecast area, we will resume posting advisories each morning, prior to 7am.

Brandon Schwartz, Avalanche Forecaster

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Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet): 30 deg. F
Max. temperature at Sierra Crest past 24 hours: 42 deg. F
Average wind direction at Sierra Crest past 24 hours: southwesterly
Average wind speed at Sierra Crest past 24 hours: 33 mph
Maximum wind gust at Sierra Crest past 24 hours: 73 mph
New snow fall at 8,200 feet past 24 hours: 0 inches
Total snow depth at 8,200 feet: 34 inches

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Mountain Weather Forecast For Today:
Cloudy skies. Rain and snow developing by mid morning
Temperature forecast for 8,000 to 9,000 feet: 30 - 35 deg. F
Ridgetop winds forecast for the Sierra Crest: Southwesterly 35 - 50 mph, gusting to 90 mph
Snowfall expected in the next 24 hours: 5 - 10 inches above 7,500'

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2 Day Mountain Weather Forecast:
7000 to 8000 Feet
Today, cloudy skies with rain and snow. Snow level 6,500' to 7,500'. Snow accumulation 1 to 2 inches. South winds at 15 to 25 mph, gusting to 35 mph. Daytime highs 38 to 43 degrees F. Tonight, cloudy skies with snow. Snow level lowering to 6,000'. Snow accumulation 3 to 6 inches. Lows 28 to 32 degrees F. Southwest winds at 15 to 25 mph, gusting to 35 mph. Thursday, cloudy skies with snow. Snow level 6,500' to 7000'. Snow accumulation 3 to 5 inches. Daytime highs 37 to 42 degrees F. Winds are forecasted to be out of the southwest at 20 to 30 mph.

Above 8000 Feet
Today, cloudy skies with snow. Snow accumulation 2 to 4 inches. South winds at 35 to 50 mph, gusting to 90 mph. Daytime highs 30 to 35 degrees F. Tonight, cloudy skies with snow. Snow accumulation 3 to 6 inches. Lows 23 to 28 degrees F. Southwest winds at 35 to 50 mph, gusting to 90 mph. Thursday, cloudy skies with snow. Snow accumulation 3 to 5 inches. Daytime highs 27 to 32 degrees F. Winds are forecasted to be out of the southwest at 30 to 45 mph, gusting to 80 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:
	Wednesday:	Wednesday Night:	Thursday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.