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 Sunday, April 22nd, 2007 at 7:00 am

The bottom line: Near and above treeline the avalanche danger is CONSIDERABLE on windloaded N-NE-E aspects 35 degrees and steeper. Below treeline the avalanche danger is MODERATE on open, recently windloaded slopes 35 degrees and steeper. Near and above treeline natural avalanche activity is possible today and human triggered activity is probable. Use safe travel techniques and avoid steep heavily windloaded terrain

It started snowing yesterday at 5pm across most of the forecast area. Overnight the storm intensified. Snowfall rates have been 2-3 inches per hour since early this morning. This storm is forecasted to drop another 6-12 inches of snow on the forecast area today. The southwest winds associated with this storm are expected to continue as long as the snowfall. Snowfall should taper off tonight and the winds should start shifting to the north and east as the storm moves out of the forecast area. By tomorrow afternoon this last hurrah of winter should be on its way east and dry, sunny weather should return to the forecast area. Temperatures should start to gradually warm up through next week.

Before it started snowing yesterday, snow surface conditions in most areas consisted of either wind scoured melt-freeze crust, shallow, unconsolidated snow on top of melt-freeze crust, or a thin breakable crust on top of shallow unconsolidated snow on top of the melt-freeze crust. There were many exposed rocks and down trees hidden beneath a dusting of snow. Overnight the storm added 9-14 inches of new snow on top of these surfaces. The 30-40mph southwest winds have wind-loaded the N-NE-E aspects creating thick wind-slabs. With another 6-12 inches of snow forecasted today and more wind, these wind slabs will become larger, more widespread, and more reactive. Added to the wind are significant snowfall rates that will cause snow to accumulate faster than it can form strong bonds with the snow on the ground. Bonding between yesterday's snow surfaces and the new snow will be suspect today. New weakness should form in the storm snow as the winds shift and the temperature changes during the storm today. Also there were still some areas where the bond between the old melt-freeze crust and the snow from last week was still weak. Overall there are several potential weakness sitting above the old melt-freeze crust with thick, heavy, wind slabs forming on top of them. This is the recipe for avalanche activity.

Any avalanche activity that occurs today is expected to initially involve new snow from the storm. Avalanches could step down to the existing melt-freeze crust in some areas. Snowpack failure occurring below the height of the uppermost melt-freeze crust in the snowpack is not expected at this time. The most significant avalanche activity should occur on recently windloaded slopes that are steeper than 35 degrees. The slopes most likely to be heavily windloaded are the N-NE-E aspects near and above treeline.

Natural avalanche activity is possible today on those slopes. Human triggered avalanches are probable in recently wind ioaded areas above treeline. Use clues like drifted snow, cornices, blowing snow, and ripples in the snow surface to determine which slopes are the most windloaded. Enjoy these last days of winter carefully: use terrain to manage your exposure to avalanche hazard toady and as always use safe backcountry travel techniques.

The bottom line: Near and above treeline the avalanche danger is CONSIDERABLE on windloaded N-NE-E aspects 35 degrees and steeper. Below treeline the avalanche danger is MODERATE on open, recently windloaded slopes 35 degrees and steeper. Near and above treeline natural avalanche activity is possible today and human triggered activity is probable. Use safe travel techniques and avoid steep heavily windloaded terrain

Due to the current storm we will not be scaling back our operations until early next week. We plan to stop issuing danger ratings Monday or Tuesday and to start issuing a snow conditions update instead. We plan to end operations for the season on April 28th.

Thank you to all of our sponsors, those individuals who purchased tickets for the SAC Ski Day fundraising events, and everyone else who donated funding this winter. We have met our operating budget for this season and have a solid start on next year's funding. For more details about our financial situation please click here.
Andy Anderson, Avalanche Forecaster

Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet): 23 deg. F
Max. temperature at Sierra Crest past 24 hours: 25 deg. F
Average wind direction at Sierra Crest past 24 hours: Southwesterly
Average wind speed at Sierra Crest past 24 hours: 40 mph
Maximum wind gust at Sierra Crest past 24 hours: 61 mph
New snow fall at 8,200 feet past 24 hours: 9-SO inches
Total snow depth at 8,200 feet: 64 inches

Mountain Weather Forecast For Today:
Snow with 6-12 inches of accumulation.
Temperature forecast for 8,000 to 9,000 feet: 23 - 28 degrees F.
Ridgetop winds forecast for the Sierra Crest: Westsouthwesterly 25 35 mph, gusting to 60 mph.
Snowfall expected in the next 24 hours: 6 - 12 inches

2 Day Mountain Weather Forecast:
7000 to 8000 Feet:
Today, snow with 6-10 inches of accumulation. Daytime highs 28 to 34 degrees F. West winds at 15 to 20 mph, gusting to 40 mph. Tonight, mostly cloudy skies with some scattered snow. Overnight lows 20 to 25 degrees F. Northwest winds at 15 to 25 mph. Sunday, partly cloudy with daytime highs 34 to 45 degrees F. Northeast winds at 15 to 20 mph are expected.
Above 8000 Feet:
Today, snow with 6-30 inches of accumulation. Daytime highs 23 to 28 degrees F. West winds at 25 to 35 mph, gusting to 60 mph. Tonight, mostly cloudy skies with some scattered snow. Overnight lows 17 to 23 degrees F. Northwest winds at 25 to 35 mph. Monday, partly cloudy with daytime highs 32 to 42 degrees F. Northeast winds at 25 to 35 mph are expected.

Backcauntry Travelers:
We want to hear from you! If you see avalanche activity, or want to share condition information for an area you've been in, please let us know. Call (530) 587-3558 or e-mail us at:

sac_avalanche@fs.fed.us

.

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.