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 28th, 2007 at 7:09 am

The bottom line: Avalanche danger near and above treeline is CONSIDERABLE on wind loaded NW-N-NE-E aspects 35 degrees and steeper. The avalanche danger is MODERATE below treeline in open areas 35 degrees and steeper.

Last night's small disturbance should be pulled farther south and east today. A few more small weather instabilities should pass through the region bringing scattered snow showers and small accumulations while a high pressure ridge builds over the eastern Pacific. This ridge should arrive over the forecast area by Friday bringing warmer temperatures and clear skies over the weekend. The ridgetop winds should continue to calm down some today and keep shifting between southwest and west.

The forecast area received another 6-9 inches of new snow overnight bringing the total amount of snow we have received in the last week to 54-65 inches. Yesterday most of the storm snow weakness related to different types of new snow crystals like graupel or needles required moderate force to cause them to fail. When the density inversion (more dense on top of less dense) that exists near the base of the new snow was isolated, it failed when slightly less force was applied. The tests performed on these layers indicate that they have started to consolidate; however, it will take some time before these weakness become very strong.

The winds did calm down some yesterday dropping to a steady 35 mph from the west southwest. This was still enough to transport snow. This new loading will cause the windslabs that have already formed throughout the storm to continue to grow all dimensions: depth, width, and extent down slope. These windslabs are stiff and hard and will easily transmit force over longer distances. Yesterday test slopes failed with a skiers weight and the slabs that fractured were between 6 inches and 2 ft thick. Most of these slabs were triggered in areas where the slab was thinnest and then stepped down into other layers in the storm snow or propagated out to areas where the slabs were thicker.

Above treeline human triggered avalanches are probable in wind loaded areas on NW-N-NE-E aspects, 35 degrees and steeper. Natural avalanches are still possible in this same terrain on steeper and more windloaded slopes. Many of the avalanches that occur today could be large, encompass the full start zone, and run full path. Most of these slides should start due to failures of the weaknesses in the storm snow and could step down to the old snow surfaces from before the storm. This would result in crowns of close to 6 ft.

Avalanche activity was reported yesterday throughout the forecast area. Many avalanches occurred in response to ski cutting or explosives. There were some natural avalanches that occurred due to cornice failure. Most of these slides occurred due to failures of weakness in the storm snow. Several of the explosive triggered avalanches stepped down to the old snow surfaces. Both natural and human triggered avalanche activity was observed across the entire width of most avalanche start zones and some of the slides ran close to full path. Crown depths between 1 and 6 feet deep were observed.

The bottom line: Avalanche danger near and above treeline is CONSIDERABLE on wind loaded NW-N-NE-E aspects 35 degrees and steeper. The avalanche danger is MODERATE below treeline in open areas 35 degrees and steeper.

At this time, we are still short $5,000 in funding for our operating budget this winter. If you use this service with any regularity and would like to continue to do so, please show your financial 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. A financial graph showing the amount of fundraising completed this season and our overall budget is available by clicking here. The financial support already received this winter from a variety of users is greatly appreciated.

Andy Anderson , Avalanche Forecaster
Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet):
9 deg. F
Max. temperature at Sierra Crest past 24 hours:
20 deg. F
Average wind direction at Sierra Crest past 24 hours:
West southwesterly
Average wind speed at Sierra Crest past 24 hours:
35 mph
Maximum wind gust at Sierra Crest past 24 hours:
56 mph
New snow fall at 8,200 feet past 24 hours:
6-10 inches
Total snow depth at 8,200 feet:
108 inches
Mountain Weather Forecast For Today:
Scattered snow showers with accumulation of up to 6".
Temperature forecast for 8,000 to 9,000 feet:
14 to 18 degrees F.
Ridgetop winds forecast for the Sierra Crest:
West 25-35 mph, gusting to 50 mph.
Snowfall expected in the next 24 hours:
6 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet
Today, scattered snow showers with accumulations of up to 3". Winds out of the southwest at 15 to 25 mph with gusts to 35 mph. Daytime highs 18 to 22 degrees F. Tonight, cloudy with scattered snow showers. West winds 10 to 20 mph. Overnight lows 11 to 17 degrees F. Thursday, cloudy with a chance of snow showers. West winds at 10 to 15 mph are expected. Daytime highs 26 to 32 degrees F.

Above 8000 Feet
Today, scattered snow showers with accumulations of up to 6". Winds out of the west at 25 to 35 mph with gusts to 50 mph. Daytime highs 14 to 18 degrees F. Tonight, cloudy with scattered snow showers. West winds 25-35 mph with gusts to 50 mph. Overnight lows 10 to 16 degrees F. Thursday, cloudy with a chance of snow showers. West winds at 15 to 25 mph with gusts to 40 are expected. Daytime highs 20 to 26 degrees F.

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.