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.

Another night of above freezing temperatures makes 4 days without lows dropping below freezing in most areas. The cloud cover cleared some last night and the winds started to decrease as the high pressure ridge over the region gains strength. Temperatures should climb even higher over the next few days in response to this strengthening ridge. Daytime highs could reach into the mid to upper 50's above 7000 ft today and into the upper 50's and low 60's in the mountains tomorrow. More sunshine and weaker winds will accompany these warmer temperatures over the next few days.

Recent Observations:

On Mt. Tallac yesterday, the snow on all aspects had already become wet and sticky by mid morning, and very little evidence of an overnight refreeze remained. In the warmer areas like under trees and on open sun exposed slopes, the upper snowpack quickly became unsupportable as the day warmed up. Runnels formed by recent melting existed on northerly aspects (photo), and sun cups had started to form on the southerly aspects. Several wet snow instabilities including roller balls, pinwheels, and loose wet snow slides had occurred on Tallac since warming started this week (photo). The largest of these existed on the sun-exposed southerly aspects with smaller instabilities present on the more shaded aspects. Snowpit data on a northerly aspect showed that melt water had only affected the top several inches of the snowpack and that below that level cold, frozen, and well consolidated snow existed (more info).

Today's Primary Avalanche Concern: Wet snow

Warmer temperatures and more sunshine today will quickly melt the weak refreeze that may have occurred last night. This melting will allow free water to percolate deeper into the snowpack and create a thicker layer of weak wet snow. High sun angles allowing sunshine to reach the northerly aspects will mean that  widespread wet snow instabilities could exist on all aspects at all elevations. Roller balls, wet loose snow avalanches, and wet slab avalanches will all remain possible today. The largest wet snow instabilities will likely occur on the most sun-exposed E-SE-S-SW-W aspects and in areas with more of the recent storm snow remaining. Wet snow instabilities remain some of the most difficult avalanche problems to accurately predict. Uncertainty surrounding the precise timing of wet snow avalanches makes conservative decision making a prudent choice under these conditions. Surface instabilities like roller balls and pinwheels and simple observations like stepping off one's skis, board, or snowmobile and sinking up to boot-top depth in wet snow can indicate potential instability on a slope.

Other things to think about: The Persistent Weak Layer

Due to the depth of the persistent weak layer and the strength of the snow above it, triggering a deep slab avalanche on NW-N-NE aspects remains unlikely. At this time data indicates collapsing this layer would require an extremely large trigger or significant weakening of the snowpack. Spring melting could eventually cause enough snowpack weakening for a deep wet slab avalanche cycle to occur. Even though data indicates conditions that could create this scenario have not yet arrived, they keep getting closer as more and more melting occurs each day and free water percolates farther into the snowpack.

The bottom line:

MODERATE avalanche danger will form quickly today on all aspects on slopes 35 degrees and steeper at all elevations in response to daytime warming.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	32-38 deg. F.
Max. temperature in the last 24 hours:	38-48 deg. F.
Average wind direction during the last 24 hours:	Southwest shifting to northwest
Average wind speed during the last 24 hours:	20 mph
Maximum wind gust in the last 24 hours:	54 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	36-88 inches

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

For 7000-8000 ft:
	Thursday:	Thursday Night:	Friday:
Weather:	Partly cloudy to mostly sunny	Partly cloudy becoming clear	Sunny with some cumulus clouds and a slight chance of thunderstorms developing in the afternoon
Temperatures:	53-60 deg. F.	35-45 deg. F.	58-65 deg. F.
Wind direction:	West shifting to the north	East	East
Wind speed:	5-15 mph	5-15 mph	5-10 mph in the morning becoming light in the afternoon
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Thursday:	Thursday Night:	Friday:
Weather:	Partly cloudy to mostly sunny	Partly cloudy becoming clear	Sunny with some cumulus clouds and a slight chance of thunderstorms developing in the afternoon
Temperatures:	45-55 deg. F.	35-45 deg. F.	48-58 deg. F.
Wind direction:	Northwest	Northeast	East
Wind speed:	10-20 mph with gusts to 40 mph	10-15 mph with gusts to 25 mph	10-15 mph becoming light in the afternoon
Expected snowfall:	O in.	O in.	O in.