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.

A weather system passing to the north of the forecast area today will spread mid and high level cloud cover over the region. Cloud cover will thin from north to south, so the southern end of the forecast area will have the greatest amount of sunshine today. Air temperatures above 8,000' are on a warming trend this morning in response to increasing southwest winds. At this time, most upper elevation remote sensors are still reporting air temperatures in the 20s. In the southern end of forecast area remote sensors above 8,000' report at least a few hours of below freezing air temperatures before warming to just above freezing this morning. After a day of calm to light ridgetop winds yesterday, increasing west winds today will build to moderate in speed as the day progresses. For tomorrow expect clearing skies, above freezing air temperatures, and moderate speed east winds.

Observations:

Observations made yesterday on Silver Peak (Pole Creek area) revealed widespread hard wind slabs on all NW-N-NE-E-SE aspects in near treeline and above treeline terrain. Hard wind slabs extended below treeline in many areas as well. These wind slabs were generally stable, with snowpit data collected near treeline at 8,000' on a N aspect, 38 degree slope indicating that fracture along the interface between the bottom of the 1 foot thick wind slab and lower density snow below was unlikely but not impossible. A firm wind scoured snow surface existed on S-SW-W aspects. Significant melting was noted in all areas of direct sun exposure up to the highpoint of travel at 8,000'. By mid day, 2 to 4 inches of wet snow existed at the snow surface on E-SE-S aspects (pit profile, more info).

Observations made yesterday on Ralston Ridge (Echo Summit area) revealed firm wind packed conditions on northerly aspects above treeline with a generally uniform dense snowpack in the top 5 feet examined. Snowpit data collected adjacent to a large intact cornice in above treeline terrain at 8,900 on a N aspect, 40 degree slope revealed no evidence of instability. Natural cornice collapse that occurred above treeline at 8,900' on a steep E aspect above Cup Lake triggered a small avalanche with a crown depth of around 1 foot. The fracture propagated a short distance to a more SE aspect portion of the slope, but not in the other direction to a more NE aspect portion of the slope (pit profile, photo, more info).

Avalanche Concern #1: Warming Instability

Significant mid and high level cloud cover over much of the forecast area today will limit the amount of solar radiation that reaches the snow surface. Over the southern portion of the forecast area, thinner cloud cover will allow for more warming and greater areas of instability today. Instability is expected to focus mainly on E-SE-S aspects at nearly all elevations. The vast majority of SW-W aspects were thoroughly scoured by gale force winds over the weekend and are not expected to hold much in the way of warming instability today. Natural cornice collapse is expected to continue this week as significant warming continues. This large trigger on the slope below may remain capable of triggering avalanche activity today. Give 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.

Avalanche Concern #2: Wind Slabs

High density wind slabs that exist in most areas near and above treeline have shown signs of stabilization over the past several days. Human triggered avalanches involving failure of these hard slabs are unlikely but not impossible in isolated areas given the right combination of terrain, weak layer, trigger, and trigger point. Continue to use good travel habits and minimize exposure to avalanche run out zones below cornices and below other backcountry travelers as clues of instability for these hard slabs will remain very few.

The bottom line:

Early this morning, avalanche danger is LOW for all elevations and aspects. As daytime warming occurs, areas of MODERATE danger will form on E-SE-S aspects at all elevations on slopes 37 degrees and steeper. For all other areas, avalanche danger will remain LOW. The greatest areas of instability today are expected to form in the southern portion of the forecast area.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	21 to 33 deg. F.
Max. temperature in the last 24 hours:	33 to 47 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	14 mph
Maximum wind gust in the last 24 hours:	35 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	127 to 193 inches

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

For 7000-8000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Cloudy skies in the north, partly cloudy skies in the south.	Partly cloudy skies.	Partly cloudy skies in the morning, then clearing.
Temperatures:	37 to 47 deg. F.	31 to 37 deg. F.	42 to 52 deg. F.
Wind direction:	W	W shifting to NW after midnight.	E
Wind speed:	10 to 15 mph with gusts to 35 mph.	Around 10 mph.	10 to 15 mph with gusts to 30 mph.
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Cloudy skies in the north, partly cloudy skies in the south.	Partly cloudy skies.	Partly cloudy skies in the morning, then clearing.
Temperatures:	30 to 40 deg. F.	24 to 34 deg. F.	35 to 45 deg. F.
Wind direction:	W	NW	NE
Wind speed:	10 to 20 mph with gusts to 30 mph. Winds increasing to 20 to 30 mph with gusts to 40 mph in the afternoon.	20 to 30 mph with gusts to 40 mph.	20 to 30 mph with gusts to 55 mph.
Expected snowfall:	O in.	O in.	O in.