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.

After a brief period this morning when isolated showers could occur in the mountains, the weather today should turn partly sunny and warm with daytime highs in the upper 40's above 7000 feet.  This spring-like weather should give way to colder snowier weather this weekend as a cold low pressure system replaces the high pressure ridge currently over the forecast area. The southwest winds should remain strong and increase to gale force during today and tonight as this system approaches. These winds will remain this strong through Saturday. Cloud cover should start to increase tonight / early tomorrow morning and some showers could begin. Snow levels should start around 7500-8500 feet allowing the initial precipitation to fall as rain. By tomorrow afternoon snow levels should drop to between 5000 and 6000 feet. The mountains above 7000 feet could see four to eight inches of snow fall tomorrow while lower elevations see a few inches.

Recent Observations:

Yesterday on Red Lake Peak above Crater Lake, a snowboard cut on a steep NE facing slope in near treeline terrain resulted in an avalanche with a crown depth of one to two feet (photo, more info). This slide measured about 75 to 100 feet in width and ran for 800 to 1000 feet down the slope. The reporting party indicated that heavy wind loading in the area had resulted in the formation of a wind slab that failed due to the slope cut. On Waterhouse Peak observations showed tender cornices above small test slopes along the summit ridge. Dropping these cornices on the wind loaded test slopes below and ski cuts on those slopes did not produce any fractures on the test slopes. Snowpit data from a more sheltered area indicated a stable snowpack in which even the deeply buried persistent weak layer showed signs of strengthening (snowpit). This data brings the number of observations showing more stable results on the deeply buried weak layer up to 6 out of 20 since March 18th. 

Today's Primary Avalanche Concern: Wet snow instability

With the cloud cover expected to decrease today, warm temperatures, sunny skies, and a weak (if at all) overnight refreeze should allow enough melting to occur for wet snow instabilities to form. Most of these instabilities should remain on the sun-exposed SE-S-SW-W aspects and manifest as roller balls, pinwheels, and wet loose avalanches. However, some small wet snow instabilities could occur on northerly aspects especially in areas where the cloud cover persists longer than expected or where rain falls/has fallen on the snowpack. Some wet slab avalanches may also become possible on slopes where the most warming occurs. Terrain hazards such as cliffs and terrain traps could increase the consequences of any size wet snow avalanches today.

Today's Secondary Avalanche Concern: Wind Slabs

As indicated by some observations yesterday, pockets of terrain still existed where wind-loading continued to occur and where the recently formed wind slabs remained fragile. The areas where these tender wind slabs persist today should decrease; however, the possibility of humans triggering wind slab avalanches will continue. These pockets of fragile wind slabs will most likely exist on N-NE-E aspects in near and above treeline terrain on the most heavily wind-loaded slopes, in complex terrain with wind loading, as well as on steep unsupported slopes.

Today's Third Avalanche Concern: Persistent Deep Slabs

In addition to the old persistent weak layer buried four to eight feet deep in the snowpack, a second layer of weak sugary snow has formed higher in the snowpack in some areas. Recent snowpit tests indicate that if either of these weak layers break the resulting fracture could propagate along the layer resulting in deep slab avalanches. Fortunately, the more shallow weak layer that would remain easier to trigger seems limited in its distribution, and a very strong deep snowpack above the older weak layer continues to prevent much force from reaching that deeply into the snowpack. Since less force can reach the weak layer, triggering a deep slab avalanche has become increasingly difficult. If one of these layers does break, tests still indicate that large destructive avalanches with serious consequences could result. These kind of avalanches will remain possible today on NW-N-NE aspects at all elevations. Areas with a shallow snowpack, areas near exposed rock outcrops and cliffs, steep unsupported slopes, complex terrain features, and slopes with trigger points represent some locations where the persistent weak layers could remain closer to the surface allowing for the possibility that people on the surface could initiate a fracture. Larger triggers like large cornice failures, other avalanches, or multiple people on the same slope could also produce these deep slab avalanches.

The bottom line:

MODERATE avalanche danger exists on all aspects at all elevations on slopes 35 degrees and steeper due to a combination of warming instability, recent wind slabs, and ongoing deep slab avalanche concerns.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	30-36 deg. F.
Max. temperature in the last 24 hours:	30-42 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	30-40 mph
Maximum wind gust in the last 24 hours:	92 mph
New snowfall in the last 24 hours:	Below 9000 ft .2 inches of rain | Snow above 9000 ft: trace to 1 inches
Total snow depth:	43-86 inches

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

For 7000-8000 ft:
	Friday:	Friday Night:	Saturday:
Weather:	Mostly cloudy with isolated rain and snow showers in the morning.	Partly cloudy with a slight chance of rain and snow after midnight.	Mostly cloudy in the morning with cloud cover increasing and snow developing by late morning.
Temperatures:	46-54 deg. F.	28-35 deg. F.	34-42 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	20-30 mph with gusts to 40 mph increasing to 25-35 mph with gusts to 55 mph in the afternoon	40-50 mph with gusts to 65 mph increasing to 55-65 mph with gusts to 90 mph after midnight.	60-70 mph with gusts to 95 mph decreasing to 50-60 mph with gusts to 85 mph in the afternoon
Expected snowfall:	trace to 0 in.	trace to 0 in.	4-8 in.
For 8000-9000 ft:
	Friday:	Friday Night:	Saturday:
Weather:	Mostly cloudy with isolated showers in the morning.	Partly cloudy with a slight chance of snow after midnight.	Mostly cloudy in the morning with cloud cover increasing and snow developing by late morning.
Temperatures:	41-47 deg. F.	24-31 deg. F.	29-35 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	35-45 mph with gusts to 60 mph	40-50 mph with gusts to 70 mph increasing to 60-70 mph with gusts to 95 mph after midnight.	65-75 mph with gusts to 100 mph increasing to 110 mph in the afternoon
Expected snowfall:	trace to 0 in.	trace to 0 in.	4-8 in.