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.

Strong southwest winds and widespread snow occurred last night as a strong cold front passed over the area. 3-6 inches of new, cold, dry snow accumulated across the forecast area. This front has also caused temperatures to plummet since yesterday. Today's highs should only climb into the low teens above 7000 ft. Temperatures should remain cold for the next several days. The cold and unstable airmass left over the area will allow light snow showers to continue today. As the front moves farther east the snow showers should become more and more isolated. The forecast only calls for a trace of new accumulation out of these scattered showers. 

Recent Observations:

Yesterday strong southwest winds started to transport snow along the Sierra Crest in near and above treeline terrain. On Donner Peak small wind slabs had formed on N-NE-E aspects, and variable conditions ranging from wind scoured surfaces to patches of soft snow existed on windward aspects (photos, more info). In more protected areas on Donner Peak, in the Deep Creek drainage, and in the Mt. Rose backcountry, the winds remained less strong little wind transport occurred. Soft unconsolidated snow remained on the northerly aspects in these areas. Some small loose snow sluffs did occur on steep N facing test slopes in the Deep Creek area (more info). On the more sun exposed S-SW-W aspects below 9000 ft in the Mt. Rose backcountry, some small wet loose snow sluffs also occurred (snowpit, more info). Snowpits, handpits, ski cuts, and general observations in these areas indicated a stable snowpack in non-wind loaded terrain yesterday.

Avalanche Problem #1: Wind Slabs

The strong southwest winds combined with 3-6 inches of new snow and the older snow available for transport have allowed wind slabs to form on the leeward NW-N-NE-E-SE aspects. While most of these wind slabs should remain less than a foot in depth and not extend very far away from the ridgelines, some larger wind slabs up to a couple feet in depth could exist in the most heavily wind loaded areas. Human triggering of these newly formed wind slabs will be possible today. As the winds shift back to the northwest today additional wind slabs could form on the E-SE-S-SW aspects. These should remain smaller than those mentioned above but could still pose a problem for backcountry travelers. Due to the strength of the winds, some wind slabs may have formed in isolated areas below treeline or in more traditionally sheltered areas.

Avalanche Problem #2: Loose-Dry Avalanches

Cold, dry snow that fell last night may not bond well to the variable snow surfaces below it. While slab formation in the new snow will be unlikely in non-wind affected areas, human triggered loose snow sluffs could easily occur today. These loose-dry avalanches should remain small and not involve enough snow to bury a person, but they could push people into undesirable areas with other consequences.

The bottom line:

Near and above treeline, the avalanche danger is MODERATE on NW-N-NE-E-SE-S-SW aspects on slopes 35 degrees and steeper due to new snow and shifting winds forming new wind slabs. Below treeline pockets MODERATE danger exist on those same aspects. Human triggered avalanches will be possible today.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	7-12 deg. F.
Max. temperature in the last 24 hours:	33-40 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	40-50 mph
Maximum wind gust in the last 24 hours:	82 mph
New snowfall in the last 24 hours:	3-6 inches
Total snow depth:	64-88 inches

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

For 7000-8000 ft:
	Thursday:	Thursday Night:	Friday:
Weather:	Mostly cloudy with scattered snow showers	Mostly cloudy with scattered snow showers in the evening. Snow diminishing overnight	Partly cloudy with a slight chance of snow showers
Temperatures:	10 to 17 deg. F.	-2 to 5 deg. F.	7 to 13 deg. F.
Wind direction:	Northwest	Northwest	Northwest
Wind speed:	15-20 mph with gusts to 30 mph	15-20 mph with gusts to 30 mph	15-20 mph with gusts to 40 mph
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Thursday:	Thursday Night:	Friday:
Weather:	Mostly cloudy with scattered snow showers	Mostly cloudy with scattered snow showers in the evening. Snow diminishing overnight	Partly cloudy with a slight chance of snow showers
Temperatures:	7 to 13 deg. F.	-5 to 2 deg. F.	9 to 15 deg. F.
Wind direction:	Northwest	Northwest	Northwest
Wind speed:	15-25 mph with gusts to 40 mph	25-30 mph with gusts to 40 mph decreasing to 15-20 mph with gusts to 35 mph after midnight	15-20 mph with gusts to 35 mph increasing to 25-30 mph with gusts to 50 mph in the afternoon
Expected snowfall:	O in.	O in.	O in.