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, April 11th, 2007 at 7:00 am

The bottom line: The avalanche danger is LOW across all elevations and aspects this morning. It will quickly rise to MODERATE near and above treeline on windloaded NW-N-NE-E aspects 35 degrees and steeper as new snow accumulates. Below treeline the avalanche danger should remain LOW with some isolated pockets of MODERATE avalanche danger forming on open, windloaded slopes 35 degrees and steeper. New snow and wind will cause human triggered avalanche activity to become possible today. Use safe backcountry travel techniques, and re-access snowpack conditions on a regular basis. Remember to be flexible and willing to change your plans when conditions change.

The first wave of the storm system is approaching the forecast area. The winds have already shifted to the southwest and started to increase and cloud cover is growing thicker. The cold air mass ahead of this storm has caused a significant drop in air temperatures. Snow levels should be around 5000 ft when the main band of precipitation reaches the mountains by mid morning. This initial wave should bring 3 to 6 inches of snow to the mountains. After this wave moves through the main low pressure system should arrive tonight and could drop another 3 to 7 inches of new snow on the mountains. Due to the northerly track of this storm areas north of Highway 50 should see the most significant accumulation. By midday tomorrow the winds are forecasted to shift to the north and east, the skies should start to clear, and the high pressure should begin to rebuild bringing warmer temperatures and clearer skies for Friday.

Lower temperatures yesterday and overnight should have allowed the snowpack to continue refreezing. The snow surface should remain frozen this morning as the storm moves in. The boundary between this cold, hard, old snow surface and the new snow could become a weak interface as the new snow accumulates and new wind slabs form during the storm. This storm is also predicted to come in waves. Each of these waves should have slightly different weather characteristics that should allow some weaknesses to form in the new snow itself. Even though the overall accumulation predicted for this storm is not huge, the winds should be able to transport snow and form significant wind slabs on leeward slopes above treeline. These wind slabs will start to form today and should become thicker, more widespread, and more reactive by tomorrow. Use clues like cornices, blowing snow, drifts, and ripples in the snow surface to determine what slopes have received wind loading. These are the slopes that will be the most worrisome and should warrant the most caution throughout this storm.

Human triggered avalanche activity should become possible today as new snow accumulates and wind wind slabs form on top of the refrozen, old snow surface. Any avalanches that do occur today should occur due to failure at the interface with the old snow surface or failure at weaknesses formed during the storm. The possibility of triggering these slides will increase today as the snow accumulates. Windloaded NW-N-NE-E aspects near and above treeline that are steeper than 35 degrees will be the most suspect. Only isolated areas of small wind slabs should develop below treeline. Human triggering of loose snow sluffs will also be possible today on any steep slopes. The avalanche danger should increase tomorrow as more snow falls overnight especially in areas north of Highway 50.

The bottom line: The avalanche danger is LOW across all elevations and aspects this morning. It will quickly rise to MODERATE near and above treeline on windloaded NW-N-NE-E aspects 35 degrees and steeper as new snow accumulates. Below treeline the avalanche danger should remain LOW with some isolated pockets of MODERATE avalanche danger forming on open, windloaded slopes 35 degrees and steeper. New snow and wind will cause human triggered avalanche activity to become possible today. Use safe backcountry travel techniques, and re-access snowpack conditions on a regular basis. Remember to be flexible and willing to change your plans when conditions change.

We will raffle a BCA backpack, beacon, shovel, and probe package on April 17th as a way to say thanks to everyone who has sent us a donation in the mail or via Pay Pal this season. All individuals who have donated $10 or more to SAC are automatically entered in this raffle. Thanks to all of our sponsors, the ski days, and everyone who has donated funding this winter, we have met our operating budget for this season and have a 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):
22 deg. F
Max. temperature at Sierra Crest past 24 hours:
42 deg. F
Average wind direction at Sierra Crest past 24 hours:
Southwest
Average wind speed at Sierra Crest past 24 hours:
15 mph through early this morning then it increased to 30 mph
Maximum wind gust at Sierra Crest past 24 hours:
42 mph
New snow fall at 8,200 feet past 24 hours:
0
Total snow depth at 8,200 feet:
53 inches
Mountain Weather Forecast For Today:
Snow developing this morning and continuing through the day. 3-6" of accumulation possible.
Temperature forecast for 8,000 to 9,000 feet:
26 - 34 degrees F.
Ridgetop winds forecast for the Sierra Crest:
Southwest at 20 to 30 mph with gusts to 50, increasing to west at 30-40 mph with gusts to 70 mph in the afternoon.
Snowfall expected in the next 24 hours:
6-12 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, snow developing this morning and continuing through the day with 3-6" of accumulation possible. Daytime highs 30 to 38 degrees F. Southwest winds at 15 to 25 mph with gusts to 35 mph. Tonight, snow with accumulations of 3-7". Overnight lows around 19 degrees F. West winds at 15 to 25 mph decreasing to 10 to 15 mph after midnight. Tomorrow, scattered snow showers then clearing with daytime highs 24 to 32 degrees F. West winds at 15 to 20 mph shifting to the north at 15 to 20 mph after noon.

Above 8000 Feet:
Today, snow developing this morning and continuing through the day with 3-6" of accumulation possible. Daytime highs 26 to 34 degrees F. Southwest at 20 to 30 mph with gusts to 50, increasing to west at 30-40 mph with gusts to 70 mph in the afternoon. Tonight, snow with accumulations of 3-7". Overnight lows around 15 degrees F. Southwest winds at 20 to 30 mph with gusts to 70 mph decreasing and shifting to west at 15 to 20 mph with gusts to 60 mph after midnight. Tomorrow, scattered snow showers then clearing with daytime highs 20 to 28 degrees F. West winds at 20 to 30 mph with gusts to 50 mph shifting to the north after noon.

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.