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, January 3, 2007 at 7:00 am

Ridgetop winds are increasing this morning ahead of the next storm system that is approaching the forecast area. Air temperatures at the upper elevations are expected to climb above freezing again today, before falling overnight and plummeting through the day tomorrow. Heavy snowfall is expected to begin during the early morning hours on Thursday.

A variable snowpack continues to exist throughout the forecast area, but is beginning to show uniform characteristics by region. At the highest elevations along the Sierra Crest where 5-6 feet of snowpack exists, the snowpack is showing excellent sintering (bonding to one another) of old faceted snow crystals at all heights within the snowpack. At lower elevations along the Sierra Crest, where only 2-3 feet of snowpack exists, significant faceting and weakening of basal rain crust layers continues to occur. In the Mount Rose area where around 2-3 feet of snowpack sits in most areas on N-NE-E aspects, highly faceted snow crystals continue to form near crusts and in the basal layer. In both the lower elevation areas of the Sierra Crest and the Mount Rose area, the upper snowpack is providing good strength and creating a stable snowpack despite weak basal layers.

Warm temperatures at the upper elevations yesterday created very wet surface snow for areas up to around 9,000' in elevation. Some human triggered roller ball activity was observed in response to skiing. Temperatures overnight dropped below freezing for a few hours, allowing for a widespread formation of a thin melt-freeze crust. Moderate to strong prefrontal westerly winds will once again redistribute snow and cause wind loading in lee areas today. Expect some small, shallow pockets of unstable wind slab to form in the most heavily wind loaded areas above treeline on N-NE-E aspects as the day progresses. Areas of wet snow instability are not impossible today in steep terrain, especially in the 7,000'- 8,000' elevation range as air temperatures warm.

For the vast majority of the forecast area, avalanche danger is LOW. Some very isolated pockets of MODERATE danger will form today above treeline on wind loaded N-NE-E aspects, 37 degrees and steeper. Pay attention for other areas of MODERATE danger where shallow wet snow instability in response to human triggers is not impossible between 7,000'- 8,000', in areas 37 degrees and steeper.

Avalanche danger will increase overnight tonight and during the day on Thursday.

Brandon Schwartz, Avalanche Forecaster

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Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet): 29 deg. F
Max. temperature at Sierra Crest past 24 hours: 46 deg. F
Average wind direction at Sierra Crest past 24 hours: westerly
Average wind speed at Sierra Crest past 24 hours: 25 mph
Maximum wind gust at Sierra Crest past 24 hours: 56 mph
New snow fall at 8,200 feet past 24 hours: 0 inches
Total snow depth at 8,200 feet: 32 inches

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Mountain Weather Forecast For Today:
Mostly cloudy skies.
Temperature forecast for 8,000 to 9,000 feet: 32 - 40 deg. F
Ridgetop winds forecast for the Sierra Crest: westsouthwesterly 40 - 50 mph, G 85 mph
Snowfall expected in the next 24 hours: 4 - 6 inches overnight

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2 Day Mountain Weather Forecast:
7000 to 8000 Feet
For today, mostly cloudy with daytime highs around 42 to 47 degrees F, decreasing to around 40 degrees F in the afternoon. Southwest winds 30 to 40 mph gusting to 60 mph in the afternoon. Overnight lows around 25 degrees F with snow developing after 10 pm. Snow accumulation 2 to 4 inches. Southwesterly winds at 30 to 35 mph gusting to 60 mph. Thursday will be cloudy with snow becoming heavy after 4 am. Snow accumulation 6 to 10 inches. Daytime highs around 30 degrees F. Southwesterly winds at 10 to 20 mph with gusts to 50 mph are expected.

Above 8000 Feet
For today, mostly cloudy with daytime highs 32 to 40 degrees F, decreasing to 32 to 36 degrees F in the afternoon. Westsouthwesterly winds 40 to 50 mph gusting to 85 mph. Overnight lows 20 to 25 degrees F with snow developing after 10 pm. Snow accumulation 4 to 6 inches. Westsouthwesterly winds at 50 to 60 mph, gusting to 100 mph after midnight. Thursday will be cloudy with snow becoming heavy after 4 am. Snow accumulation 8 to 12 inches. Daytime highs around 20 degrees F, decreasing as the day progresses. Winds out of the westsouthwest at 30 to 45 mph, gusting to 70 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.