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.

Snowfall began yesterday afternoon and continued into the overnight hours. A quick 8 to 14 inches of new snow has accumulated across the forecast area in the last 18 hours. Ridgetop winds remain out of the west early this morning and have decreased from strong to moderate in speed. Winds are expected to continue to decrease in speed and shift as the day progresses. Sunny skies, moderate speed north to east winds, and air temperatures near freezing at the 7,500' level are expected for today.

Observations:

Observations made yesterday on Hidden Peak (West Shore Tahoe area) revealed significant wind transport of old snow prior to the onset of snowfall (video). Surface wind slabs along the summit ridge near treeline at 9,150' on N-NE aspects were increasing in density but showed no skier triggered cracking or collapse at 11:45 am, about 45 minutes prior to the onset of significant snowfall in that area. At lower elevations, free water was noted within the top 0.25 to 0.5 inch of the snowpack on N-NE aspects below 7,800' and up to 8,500' on open E aspects. After the onset of snowfall yesterday, air temperatures have maintained a constant cooling trend through this morning. Snowpack data collected this morning by the Alpine Meadows Professional Ski Patrol from their snow study plot at 6,800' indicated good bonding to the melt freeze crust at the base of the new snow and one easy shear within the new snow.

Avalanche concern #1: Warming instability

A rapid transition from storm conditions to sunny skies under mid March solar radiation is expected to cause areas of warming instability. Natural point release and possibly slab avalanches as well as human triggered slab and loose snow avalanches large enough to bury or injure and person are expected today. Warming instability will mainly occur on E-SE-S aspects below 8,500' but is possible on other sun expose aspects and at higher elevations.

Avalanche concern #2: Wind slabs

Visible evidence of natural slab avalanche activity that occurred overnight is anticipated in the backcountry. Human triggered avalanches involving the recent storm snow remain possible today in recently wind loaded areas. This will mainly occur in near and above treeline terrain on NW-N-NE-E aspects, but is possible in open wind affected areas below treeline as well. The cooling trend observed since the onset of snowfall typically lends to better stability, so avalanche activity may occur within greater areas of seemingly stable snow. Once ridgetop winds shift to the NE-E later this morning, some scouring of above treeline avalanche start zones may occur. Thicker slabs will remain near treeline and in other areas with more protection from moderate speed NE-E winds.

 

The bottom line:

Avalanche danger is CONSIDERABLE below 8,500' on E-SE-S aspects 35 degrees and steeper due to warming instability. Avalanche danger is MODERATE both above and below treeline on all other aspects 35 degrees and steeper.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	10 to 14 deg. F.
Max. temperature in the last 24 hours:	30 to 34 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	55 mph
Maximum wind gust in the last 24 hours:	89 mph
New snowfall in the last 24 hours:	8 to 14 inches
Total snow depth:	100 to 135 inches

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

For 7000-8000 ft:
	Saturday:	Saturday Night:	Sunday:
Weather:	Partly cloudy skies.	Clear skies.	Sunny skies.
Temperatures:	23 to 29 deg. F.	15 to 20 deg. F.	37 to 44 deg. F.
Wind direction:	NW shifting to NE by late morning.	NE to E	E
Wind speed:	10 to 15 mph with gusts to 25 mph. Winds 10 to 20 mph after wind shift.	10 to 20 mph with gusts to 30 mph.	10 to 15 mph.
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Saturday:	Saturday Night:	Sunday:
Weather:	Partly cloudy skies.	Clear skies.	Sunny skies.
Temperatures:	18 to 23 deg. F.	15 to 20 early, rising in to the upper 20s overnight. deg. F.	35 to 41 deg. F.
Wind direction:	NW shifting to NE by late morning.	NE	NE
Wind speed:	15 to 25 mph with gusts to 45 mph. Winds decreasing to 15 to 20 mph with gusts to 35 mph.	15 to 25 mph with gusts to 45 mph.	10 to 20 mph with gusts to 40 mph in the morning.
Expected snowfall:	O in.	O in.	O in.