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.

Some cloud cover last night kept temperatures warmer than on previous nights. Remote weather sensors report above freezing temperatures up to around 8400 ft. this morning. Above this elevation most areas did drop below freezing for a few hours early this morning. The clouds should clear out as a high pressure ridge establishes itself over the forecast area. This high pressure will bring mostly sunny skies and warmer temperatures to the region today. Tonight the forecast calls for clear skies and overnight lows in the upper 20's above 7000 ft. Tomorrow should be a typical Tahoe spring day with lots of sun and daytime highs in the upper 40's above 7000 ft. During the next 24 hrs the east winds that started yesterday should remain light to moderate and should decrease some tomorrow.

Observations:

Yesterday on Donner Summit, a hard, frozen melt-freeze crust existed on the previously sun-exposed aspects in the morning. By mid afternoon on Andesite Ridge (pit profile, more info), 3-5 inches of wet snow existed on the southerly aspects. Several roller balls had also occurred on the sun-exposed, southerly slopes by this time. Ski cuts on steep southerly test slopes produced more roller balls but no wet slab failures or large wet point release avalanches. Wind-affected snow also remains in many near and above treeline areas with hard wind slabs on the NW-N-NE-E-SE aspects and wind-scoured surfaces that are changing into melt-freeze surfaces on the S-SW-W aspects. Some large and potentially unstable cornices also still remain above the most wind-loaded slopes in near and above treeline terrain in this area. Farther south on the S-SE aspects of Poulsen Peak, large roller balls and small wet point releases occurred by 2pm yesterday.

Avalanche Concern #1: Warming Instability

Warmer overnight temperatures and some cloud cover during the night should have caused a weaker and more shallow overnight refreeze. As the sun comes out and the temperatures climb today, they will quickly melt the the refrozen melt-freeze snow. This melting should progress deeper into the snowpack today than it did yesterday. As melting occurs, the snowpack will weaken enough for wet snow instabilities to become possible today. The weak overnight refreeze, more sun, and warmer temperatures should allow these kinds of instabilities to become more widespread today. Roller balls and wet point releases should comprise most of the wet snow instabilities. Some wet slabs may be possible as well. The previously wind-loaded, sun-exposed E-SE-S aspects will hold the best potential for serious wet snow problems; however, some of these problems could also develop on sun-exposed but wind scoured SW and W aspects.

Avalanche Concern #2: Wind Slabs and Large Cornice Failure

The hard wind slabs formed during last week's storm continue to consolidate and have become more difficult to trigger. Natural and human-triggered avalanches involving these wind slabs remain unlikely but not impossible. If the right trigger impacts the right slope at the right spot some of these slabs may still fail in very, very isolated areas. Very large triggers much larger than a person or a snowmobile could also still cause these dense slabs to fail. Unfortunately, many of the slopes that have these wind slabs also have very large triggers sitting above them in the form of cornices the size of trains. These heavy cornices hanging over the wind loaded slopes remain sensitive to human triggering and could still break naturally especially as the warmer temperatures and sunshine melt the bonds holding them together. Most of these large cornices extend several feet out over the slopes and will break several feet away from their edge. Regardless of whether or not cornice failure causes avalanches on the slopes below, the large pieces of cornice rolling down a slope could easily crush or injure a person standing in their path or tumbling downhill with them. Respect to this potential hazard by staying well back from cornice edges and by not stopping or gathering with other travelers on the lower portions of slopes directly below large cornice features.

The bottom line:

Early this morning, avalanche danger is LOW for all elevations and aspects. MODERATE danger quickly will form on E-SE-S aspects with pockets of MODERATE danger forming on SW-W aspects at all elevations on slopes 37 degrees and steeper due to daytime warming. Even though human-triggered and natural avalanches remain unlikely, large dangerous natural and human-triggered cornice collapses remain likely.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	31-36 deg. F.
Max. temperature in the last 24 hours:	34-45 deg. F.
Average wind direction during the last 24 hours:	West southwest shifting to the east northeast
Average wind speed during the last 24 hours:	25-35 mph
Maximum wind gust in the last 24 hours:	78 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	124-189 inches

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

For 7000-8000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Mostly cloudy in the morning then clearing in the afternoon.	Clear	Sunny
Temperatures:	42-52 deg. F.	29-36 deg. F.	47-57 deg. F.
Wind direction:	Northeast	Northeast	Northeast
Wind speed:	10-15 mph with gusts to 30 mph	10-15 mph with gusts to 30 mph	around 10 mph with gusts to 25 mph
Expected snowfall:	O in.	00 in.	O in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Mostly cloudy in the morning then clearing in the afternoon.	Clear	Sunny
Temperatures:	35-45 deg. F.	26-36 deg. F.	37-47 deg. F.
Wind direction:	Northeast	Northeast	Northeast
Wind speed:	20-30 mph with gusts to 55 mph	15-25 mph with gusts to 40 mph	10-15 mph with gusts to 30 mph
Expected snowfall:	O in.	O in.	O in.