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.

The high-pressure ridge should bring slightly warmer temperatures and clear skies to the forecast area today. After blowing from the west during the day yesterday, the winds shifted to the northeast and east last night. Today, the winds should decrease in speed and continue out of the east. Tonight, some clouds should start to build over the region and the winds should shift back to the south and southwest. By tomorrow, expect to see stronger southwest winds and more cloud cover ahead of a strong low-pressure system due to impact the area on Monday night. Temperatures should remain warm for one more day tomorrow before this storm reaches the area. See the Reno NWS page for more information on this upcoming pattern change (wx graphic).

Observations:

Observations on Castle Peak (Donner Summit area) and Miess Ridge (Carson Pass area) yesterday showed that the westerly winds continued to transport snow onto on the leeward slopes near and above treeline. In the Castle Peak area, this continued loading added to Wednesday's wind slabs. In the Meiss Ridge area, where Wednesday's wind slabs were smaller and more variable in distribution, the new snow hid these slabs below 2-4 inches snow making it difficult to know where Wednesday's wind slabs still exist. Layer bonding tests in these areas indicated that the graupel layer (snow's equivalent to ball bearings) 2-3 inches above the base of the Wednesday's snow had gained some strength. However, hard ski cuts on a 38 degree, N-NE facing,  wind-loaded test slope at 8200' in the Castle Peak area still caused this graupel layer to break and release a 1-2 ft deep, 20 ft wide, 10 ft long slide. Below treeline on non-wind-affected slopes, 2-5 inches of new snow sat on top of old crusts in most areas. More snow (4-8 inches) accumulated in the northern end of the forecast area. On the E-SE aspects below 8000' in the Castle Peak area, the new snow grew wet and sticky by mid afternoon and some small, skier-triggered sluffs started to occur on isolated slopes. 

Avalanche concern #1: Wind Slabs

Wind slabs will remain the primary avalanche concern today. The largest and most tender wind slabs should still exist on the wind loaded, N-NE-E aspects near and above treeline north of Lake Tahoe. These slabs should become smaller and more isolated but harder to recognize in the southern half of the forecast area. Some wind slabs also still remain on cross loaded NW and SE aspects in near and above treeline terrain. Even though these slabs should be more difficult to trigger today due to settlement in the snowpack and the east winds removing snow from them, human triggering of these wind slabs will remain possible.  As the winds shift to the east today, they will move more snow onto the NW-W-SW aspects adding size to the current wind slabs on the NW aspects and creating some new slabs on the W and SW aspects near and above treeline. As these slabs continue to grow human triggering of wind slabs on these slopes will also become possible in isolated areas.

Avalanche concern #2: Warming instabilities

As the intense March sun hits the new snow, some isolated areas of instability may form on sun-exposed aspects. Most of these instabilities should present as roller balls and point-release slides; however, some slab avalanches could occur especially on steep, SE-facing slopes with new snow on them. These warming instabilities should be most common on SE-S-SW aspects below 8000', but they are not impossible at some of the higher elevations on the most sun-exposed slopes.

The bottom line:

Pockets of MODERATE avalanche danger exist on all aspects on slopes 35 degrees and steeper at all elevations. Shifting winds causing wind loading on various slopes and increased daytime warming will comprise the main avalanche concerns today.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

Weather Observations from along the Sierra Crest between 8200 ft and 8800 ft:

0600 temperature:	22 deg. F.
Max. temperature in the last 24 hours:	28-35 deg. F.
Average wind direction during the last 24 hours:	Northeast shifting to west shifting back to the east and northeast
Average wind speed during the last 24 hours:	20-30 mph
Maximum wind gust in the last 24 hours:	53 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	86-124 inches

Two-Day Mountain Weather Forecast - Produced in partnership with the Reno NWS

For 7000-8000 ft:
	Saturday:	Saturday Night:	Sunday:
Weather:	Sunny	Clear becoming partly cloudy after midnight.	Mostly cloudy
Temperatures:	38-45 deg. F.	23-30 deg. F.	43-50 deg. F.
Wind direction:	East	South	Southwest
Wind speed:	10-15 mph with gust to 25 mph	10 -15 mph	10-15 mph with gusts to 30 mph increasing to 20-30 mph with gusts to 50 mph in the afternoon
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Saturday:	Saturday Night:	Sunday:
Weather:	Sunny	Clear becoming partly cloudy after midnight.	Mostly cloudy
Temperatures:	34-41 deg. F.	22-29 deg. F.	43-49 deg. F.
Wind direction:	East	South shifting to the southwest after midnight	Southwest
Wind speed:	15-20 mph with gusts to 30 mph	10-15 mph with gusts to 25 mph increasing to 15-25 mph with gusts to 35 mph after midnight	20-35 mph with gusts to 50 mph increasing to gusts to 60 mph in the afternoon
Expected snowfall:	O in.	O in.	O in.