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 weather system that affected the forecast area yesterday produced colder than expected air temperatures and more new snow accumulation than expected in many areas. Instead of a trace to 1 inch of new snow, 2 to 6 inches of new snow accumulated across the forecast area. Air temperatures above 6,500' did not warm above 25 to 28 degrees during the past 24 hours. Remote sensors are reporting air temperatures this morning around 8,500' at around 20 degrees. High cloud cover and above freezing air temperatures below 9,000' are forecast for today. Ridgetop winds were moderate to strong in speed out of the west yesterday. Winds shifted to northwest overnight and decreased to light in speed. Generally light west to southwest winds are expected for today. A weak weather system passing mainly to the north of the forecast area tomorrow is expected to bring increased cloud cover, above freezing air temperatures, and a slight chance rain and snow showers to the region.

Observations:

Observations made yesterday morning on Rose Knob Peak (Mount Rose area) revealed snow surface melting of the top few mm of the snow surface existed below 8,100' in areas of direct sun exposure during the morning hours prior to the onset of snow shower activity. The snow surface was observed to refreeze during periods of snow showers and melt during sun breaks. Only light snow showers occurred in this area prior to 11 am with no measurable accumulation at that time. Snowpit data collected at treeline on a SE aspect at 8,800' revealed a very hard melt freeze surface crust 15 inches thick (pit profile, more info).

Observations made late yesterday afternoon along the east ridge of Ralston Peak (Echo Summit area) revealed 4 to 6 inches of new snow accumulation with occasional small pockets of wind loaded snow up to 10 inches deep in lee areas. The texture of the melt affected old snow surface was clearly visible under the new snow. Good bonding was noted at the old/new snow interface with no evidence of significant slab formation or instability observed. Sluffing occurring within the new snow was easily skier triggered in steep areas, but minimal amounts of new snow became entrained in the sluffs (photo, video, more info).

Primary Avalanche Concern: Warming Instability

Despite the high cloud cover, significant amounts of solar radiation will reach the snow surface today. As the day progresses, areas of wet snow instability will likely form in areas where new snow from yesterday receives significant sun exposure. This is expected at all elevations on E-SE-S-SW-W aspects as well as on sun exposed NE aspects especially at the mid and lower elevations. Due to the lack of slab instability noted yesterday in areas where up to 6 inches of new snow accumulated and many areas where new snow amounts were much closer to 2 inches, wet snow instability today is expected to take the form of wet loose snow avalanches. Some small natural wet point release avalanches may occur today, but the main concern is for medium size human triggered wet loose snow avalanches in areas where the greatest amounts of new snow accumulation occurred yesterday.

Secondary Avalanche Concern: Wind Slabs

Observations from yesterday indicate that wind loading up to 10 inches deep occurred in some lee areas. An isolated human triggered slab avalanche around 1 foot deep is unlikely but not impossible today in near and above treeline terrain on steep N-NE aspects in areas where the greatest amounts of new snowfall accumulated yesterday. Instability associated with daytime warming on sun exposed NE-E aspects is more likely to contribute to human triggered avalanches today than wind slab formation alone.

The bottom line:

Early this morning, avalanche danger is LOW for all elevations and aspects. Avalanche danger will rise to MODERATE in sun exposed areas both above and below treeline on NE-E-SE-S-SW-W aspects on slopes 35 degrees and steeper in response to daytime warming.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	18 to 21 deg. F.
Max. temperature in the last 24 hours:	21 to 28 deg. F.
Average wind direction during the last 24 hours:	West
Average wind speed during the last 24 hours:	31 mph
Maximum wind gust in the last 24 hours:	53 mph
New snowfall in the last 24 hours:	2 to 6 inches
Total snow depth:	100 to 165 inches

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

For 7000-8000 ft:
	Thursday:	Thursday Night:	Friday:
Weather:	High clouds.	Mostly cloudy skies.	Mostly cloudy skies with a slight chance of showers.
Temperatures:	37 to 43 deg. F.	20 to 27 deg. F.	45 to 51 deg. F.
Wind direction:	W	SW	SW
Wind speed:	Up to 10 mph.	10 to 15 mph.	15 to 25 mph with gusts to 35 mph.
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Thursday:	Thursday Night:	Friday:
Weather:	High clouds.	Mostly cloudy skies.	Mostly cloudy skies with a slight chance of snow showers.
Temperatures:	28 to 36 deg. F.	21 to 27 deg. F.	37 to 45 deg. F.
Wind direction:	W	SW	SW
Wind speed:	10 to 15 mph with gusts to 25 mph.	10 to 20 mph with gusts to 35 mph.	20 to 30 mph with gusts to 50 mph. Gusts increasing to 60 mph in the afternoon.
Expected snowfall:	O in.	O in.	0 to trace in.