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, February 23nd, 2007 at 6:45 am

The bottom line: Near and above tree line avalanche danger is MODERATE on slopes that are not wind affected. On NW-N-NE-E wind loaded slopes steeper than 35 degrees the avalanche danger is CONSIDERABLE. Below tree line avalanche danger is MODERATE. Remember that MODERATE avalanche danger means that human triggered avalanches are possible.

The first of several storms expected to move through the area should be moving east by midday. It will leave cold clear weather and calmer winds over the forecast area for the rest of today. Currently, the trend is for northwest flow aloft to continue bringing unsettled stormy weather to our forecast area. By tonight the winds should shift as the next storm approaches. Tomorrow the leading edge of this storm should arrive bringing light snow for the daytime hours. Most of the moisture associated with the next storm should arrive Saturday night as more snow. The precipitation and stormy weather is expected to persist through the weekend.

Yesterday's storm left a blanket of 22-30 inches snow across the forecast area. Significant wind transport and windloading occurred due to the strong southwest and west southwest winds. By the afternoon reactive windslabs had formed on most of the leeward NW-N-NE slopes. Slopes that are normally less affected by windloading had been crossloaded. These slabs and windloaded areas continued to grow through the night as 10-16 inches of new snow fell accompanied by continued winds. Even though the winds are supposed to be slightly calmer today, they should still be strong enough to transport snow. The winds are also forecasted to shift even more to the west, so as the windslabs that formed yesterday expand, new windslabs will form on the more easterly aspects. Today the winds should also rework some of the wind affected snow from yesterday creating windslabs that are stiffer and more dense. All of the new snow including these windslabs sits on an old snow surface that is a mix of weak grains and hard, slippery surfaces. Yesterday poor bonding between these old snow surfaces and the new snow was observed. Weakness within the new snow that formed as a result of changes in the storm conditions were also observed. Ski cutting of test slopes and known avalanche paths on northerly aspects resulted in failures on the weakness in the new snow, and many explosive triggered avalanches ran on the old/new snow interface yesterday. While the air temperatures remain cold, it will take longer for these weakness to consolidate. Human triggered avalanches are possible today on most aspects and probable on on NW-N-NE-E windloaded slopes steeper than 35 degrees. Some sluffs may also occur on slopes steeper than 35 degrees. On the most heavily windloaded slopes steeper than 35 degrees natural avalanche activity is possible. Most avalanches should fail on weaknesses in the new snow formed as conditions changed during the storm or on the interface with the old snow surfaces.

Today is a day to be cautious and conservative in terrain choices. There are plenty of great tree runs, mellow slopes, and ridgelines with lots of new, low density powder on them. Even though the winter has been sparse, don't let "powder fever" and big, commiting lines overrule good judgment.

Yesterday numerous avalanches were reported on steep windloaded slopes. Most of these were triggered by explosives or intentional ski cutting after midday. For a list of backcountry avalanche activity reported to the Sierra Avalanche Center this season, click here.

The bottom line: Near and above tree line avalanche danger is MODERATE on slopes that are not wind affected. On NW-N-NE-E wind loaded slopes steeper than 35 degrees the avalanche danger is CONSIDERABLE. Below tree line avalanche danger is MODERATE. Remember that MODERATE avalanche danger means that human triggered avalanches are possible.

At this time, we are still short $8,000 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:
0400 temperature at Sierra Crest (8,700 feet):
12 deg. F
Max. temperature at Sierra Crest past 24 hours:
23 deg. F at 8AM yesterday.
Average wind direction at Sierra Crest past 24 hours:
West southwest
Average wind speed at Sierra Crest past 24 hours:
35 mph
Maximum wind gust at Sierra Crest past 24 hours:
104 mph
New snow fall at 8,200 feet past 24 hours:
12-18 inches
Total snow depth at 8,200 feet:
63 inches
Mountain Weather Forecast For Today:
Mostly cloudy with scattered snow showers.
Temperature forecast for 8,000 to 9,000 feet:
17 to 23 degrees F.
Ridgetop winds forecast for the Sierra Crest:
West 25-35 mph gusting to 50 mph.
Snowfall expected in the next 24 hours:
Trace
2 Day Mountain Weather Forecast:

7000 to 8000 Feet
Today mostly cloudy with scattered snow showers. Winds should be out of the west at 15-25 mph gusting to 35 mph. Daytime highs around 25 degrees F. Tonight, mostly cloudy. Northwest winds 10 to 15 mph. Overnight lows 15 to 23 degrees F. Saturday, snow with accumulations up to 2 inches. Winds out of the northwest at 15 to 25 mph with gusts to 40 mph in the afternoon. Daytime highs 32 to 38 degrees F.

Above 8000 Feet
Today mostly cloudy with scattered snow showers. Winds should be out of the west at 25-35 mph gusting to 50 mph. Daytime highs 17 to 23 degrees F. Tonight, mostly cloudy. Northwest winds 15 to 20 mph with gusts to 50 mph. Overnight lows around 18 degrees F. Saturday, snow with accumulations up to 2 inches. Winds out of the northwest at 25 to 35 mph with gusts to 70 mph in the afternoon. Daytime highs around 29 degrees F.

Backcountry 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:
	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.