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 Friday, April 6th, 2007 at 7:00 am

The bottom line: This morning, avalanche danger is LOW for all elevations and aspects. For all elevations and aspects in areas where afternoon thunderstorms do occur today, the avalanche danger will rise to MODERATE on any slopes that receive rain and are steeper than 35 degrees. Above 8,000' as daytime warming occurs, avalanche danger will rise to MODERATE on sun exposed E-SE-S-SW aspects 35 degrees and steeper. Below 8,000', avalanche danger will rise to MODERATE on all snow covered aspects, 35 degrees and steeper that receive sun today.

Yesterday's widespread cloud cover dissipated last night. The clear skies should only last for a short time before a convective weather pattern starts forming new clouds over the Sierra today. By this afternoon scattered thunderstorms are possible along the Sierra Crest and in the Mount Rose area. Temperatures are expected remain high through today and freezing levels should be above 9000'. As a low pressure system near the California coast begins to move inland, the convective cycle should continue, but temperatures should cool down some. When this low passes to the east, a stable warm high pressure system is forecasted to move in at the beginning of next week. Today the winds should be relatively calm. They should increase and shift to the southwest as the low pressure system moves close to the area on Saturday.

Air temperatures across the forecast area have been very warm for the last few days. Yesterday's high temperatures along the Sierra crest topped out between 56 and 63 degrees F. Overnight lows never fell below the mid 40's again last night. Today will be the forth day in a row that temperatures have stayed well above freezing around the clock. Yesterday's cloud cover prevented as much direct solar radiation from reaching the snow surface. This decrease in direct solar radiation cause the weak refreeze of two nights ago to melt less than I thought it would on the southerly aspects yesterday. The clouds also allowed more indirect radiation to reach more different aspects and served as a greenhouse to keep air temperatures higher than normal. These facts mean that even though the cloud cover cleared last night and some radiational refreeze of the snowpack occurred, the snowpack should soften very quickly today as the sun comes out this morning. In areas where the snowpack is exposed to the sun a deeper layer of wet unconsolidated snow will form in comparison to previous days. This melting will create free water in the snowpack that will weaken the snowpack and create areas of wet snow instability. If scattered afternoon thunderstorms develop today, the rain that falls will help to destabilize the snowpack by quickly contributing a significant amount of free water and warmth to a snowpack that is already relatively warm. The rain will make wet snow instability much more widespread.

Snow surface conditions vary widely from rough and bumpy to smooth and enjoyable. The late-spring-like weather has caused daily melt-freeze cycles to occur in most of the forecast area. The only areas that are still have not seen several melt-freeze cycles are northerly aspects above 10,000'. Many northerly aspects above 9,000' still have not undergone enough melt-freeze cycles for the snow from the last storm to become high quality corn snow. In these areas only a thin melt-freeze crust exists on the snow surface. Human triggered rollerballs and pinwheels continue to be reported in the Carson Pass area on these aspects. Below 9,000', excellent corn snow conditions can be found mid morning in many areas, especially on E and SE aspects.

Any avalanche activity is unlikely prior to mid morning unless some rain showers occur. If it does rain today human triggered avalanches will be possible on any slopes that receive rain and are steeper than 35 degrees. The sun will also help areas of wet snow instability to form on steep slopes in a variety of areas. Human triggered avalanches will become possible above 8,000' on sun exposed E-SE-S-SW aspects, 35 degrees and steeper. Below 8,000', human triggered avalanches will become possible on all snow covered aspects, 35 degrees and steeper.

Keep in mind that when boot penetration in wet snow exceeds boot top height, human triggered wet snow avalanches are possible in that area. Step off of your equipment on a regular basis to check boot penetration. When evidence of wet snow instability such as deep boot penetration or pinwheels larger than 1 foot in diameter develop, move to a less soft and sloppy aspect or call it a day.

The bottom line: This morning, avalanche danger is LOW for all elevations and aspects. For all elevations and aspects in areas where afternoon thunderstorms do occur today, the avalanche danger will rise to MODERATE on any slopes that receive rain and are steeper than 35 degrees. Above 8,000' as daytime warming occurs, avalanche danger will rise to MODERATE on sun exposed E-SE-S-SW aspects 35 degrees and steeper. Below 8,000', avalanche danger will rise to MODERATE on all snow covered aspects, 35 degrees and steeper that receive sun today.

The Heavenly Ski Patrol has been generous enough to include the Sierra Avalanche Center as one of the benefactors of their annual fundraising party this year. The party is this Friday, April 6th at the Horizon Casino Resort in South Lake Tahoe from 7pm to midnight. Tickets are $10 at the door. A portion of the proceeds will go to the SAC operating budget for next season. For more information please click here. We will also raffle off 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):
46 deg. F
Max. temperature at Sierra Crest past 24 hours:
56-63 deg. F
Average wind direction at Sierra Crest past 24 hours:
Southeasterly
Average wind speed at Sierra Crest past 24 hours:
5 mph
Maximum wind gust at Sierra Crest past 24 hours:
21 mph
New snow fall at 8,200 feet past 24 hours:
0 inches
Total snow depth at 8,200 feet:
57 inches
Mountain Weather Forecast For Today:
Clear skies this morning becoming mostly cloudy this afternoon with some isolated thunderstorms possible.
Temperature forecast for 8,000 to 9,000 feet:
52-60 degrees F.
Ridgetop winds forecast for the Sierra Crest:
Easterly at 10 to 15 mph
Snowfall expected in the next 24 hours:
0 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today clear skies this morning becoming mostly cloudy this afternoon with a chance of isolated thunderstorms. Daytime highs 56 to 64 degrees F. East winds at 10 to 15 mph. Tonight, mostly cloudy skies with a chance of isolated showers. Overnight lows 36 to 42 degrees F. West winds at 10 to 15 mph. Saturday, mostly cloudy skies with isolated showers in the morning and a chance of thunderstorms in the afternoon. Daytime highs 52 to 60 degrees F. Southwest winds at 15 to 25 mph are expected.

Above 8000 Feet:
Today clear skies this morning becoming mostly cloudy this afternoon with scattered thunderstorms. Daytime highs 52 to 60 degrees F. East winds at 10 to 15 mph. Tonight, mostly cloudy skies with a chance of scattered thunderstorms. Overnight lows 36 to 42 degrees F. Southwest winds at 10 mph after midnight. Saturday, mostly cloudy skies with isolated showers in the morning and a chance of thunderstorms and snow in the afternoon. Daytime highs 47 to 55 degrees F. Southwest winds at 20 to 30 mph are expected.

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