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 February 24, 2008 7:00 AM
Click here for a detailed map of the SAC forecast area

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Today's Advisory:

The avalanche danger is CONSIDERABLE near and above treeline on wind loaded NW-N-NE-E aspects, 35 degrees and steeper. Below treeline, avalanche danger is MODERATE on open slopes steeper than 37 degrees.

Since the onset of this storm yesterday afternoon the winds have averaged over 55 mph along the ridgetops and around 14 inches of 12% to 14% snow has fallen on the Sierra Crest. The Mount Rose area received closer to 19 inches of 11% snow. After a small break in snowfall this morning precipitation should increase again as the center of the low pressure system moves onshore. The forecast calls for another 8 to 16 inches of snow accumulation above 7000' today and stronger southwest winds. This storm should weaken quickly as it moves east. Tomorrow a high pressure ridge should start to rebuild over the forecast area.

The strong winds and new more dense snow will have formed new wind slabs on top of the lighter snow from earlier this week creating a density inversion (heavy snow on top of lighter snow) in the upper snowpack. By yesterday afternoon small (5 to 10 feet wide with 3 inch crowns) skier triggered soft slab avalanches started to occur in the Angora Peak area as a result of failure at this density change. These wind slabs will also add more weight and stress to the interface between the old snow surfaces and the new snow that fell earlier this week. Even though observations and layer bonding tests yesterday from Deep Creek north of Squaw and Angora Peak (south of Mt. Tallac) show that interface gained some strength it may not be enough to withstand the additional load.

More new snow, continued wind loading, and the presence of weak layers within the storm snow as well as a moderately weak interface between the old snow surfaces and previous new snow mean that natural avalanche activity is possible today on steep wind loaded slopes near and above treeline. Human triggered avalanche activity is probable today on these slopes. Avalanches should start by failing on weakness formed within the most recent new snow (graupel layers or the density inversion) and could easily step down to the old snow surfaces creating deeper, larger slides. Below treeline less wind and snow and stronger bonding at the old snow surfaces means smaller, less sensitive slabs. Natural avalanche activity is unlikely below treeline but human triggerable slabs could exist on steep, open slopes.

The bottom line: The avalanche danger is CONSIDERABLE near and above treeline on wind loaded NW-N-NE-E aspects, 35 degrees and steeper. Below treeline, avalanche danger is MODERATE on open slopes steeper than 37 degrees.

Please send us your snow, weather, and avalanche observations by clicking the submit observations link on our contact page.

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: 25 deg. F.
Average wind direction at Sierra Crest past 24 hours: Southwest
Average wind speed at Sierra Crest past 24 hours: 25 mph until 2pm yesterday, since then 55-60 mph
Maximum wind gust at Sierra Crest past 24 hours: 108 mph
New snow fall at 8,200 feet past 24 hours: 14 inches along the Sierra Crest and 19 inches in the Mount Rose area
Total snow depth at 8,200 feet: 104 inches
Mountain Weather Forecast For Today:
After a short break in snow fall this morning snow should increase mid morning and continue for the rest of the day.
Temperature forecast for 8,000 to 9,000 feet: around 25 deg. F
Ridgetop winds forecast for the Sierra Crest: Southwest at 40 to 60 mph with gusts to 100 mph.
Snowfall expected in the next 24 hours: 12 to 16 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, snow with accumulation of 4 to 8 inches. Daytime highs around 30 deg. F. Southwest winds at 20 to 30 mph with gusts to 50 mph.

Tonight, snow showers tapering off overnight with accumulation up to 4 inches. Overnight lows 16 to 22 deg. F. Southwest winds at 20 to 30 mph with gusts to 45 mph shifting to the west and decreasing to 15 to 20 mph with gusts to 30 mph.

For Monday, partly cloudy skies with daytime highs around 37 deg. F. West winds at 10 mph shifting to the northeast.

Above 8000 Feet:
Today, snow with accumulation of 8 to 12 inches. Daytime highs around 25 deg. F. Southwest winds at 40 to 60 mph with gusts to 100 mph.

Tonight, snow showers tapering off overnight with accumulation up to 4 inches. Overnight lows around 18 deg. F. Southwest winds at 30 to 40 mph with gusts to 65 mph shifting to the west and decreasing to 20 to 30 mph with gusts to 45 mph.

For Monday, partly cloudy skies with daytime highs around 33 deg. F. Northwest winds at 10 to 15 mph with gusts to 25 mph shifting to the north.

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:
	Sunday:	Sunday Night:	Monday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.