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 storm system that affected the region yesterday has moved south and east of the area. It did leave two to seven inches of new snow in its wake. More snow fell in the southern part of the forecast area. The Bear Valley / Ebbetts Pass area recorded the most snow accumulation with close to seven inches in the last 24 hours. Farther north less snow fell with areas north of Echo Summit only picking up one to three inches. Scattered snow showers and widespread cloud cover should continue through tomorrow due to unsettled weather behind this system.The southwest winds should remain light today, but they should start to increase tomorrow as a much stronger and snowier storm approaches the area for Tuesday night.

Recent Observations:

On Stevens Peak and on Becker Peak snowpack observations showed that a very strong and moist snowpack three to four feet deep sits above the persistent weak layer of sugary snow (facets). In both areas observations indicated that this weak layer has started to gain some strength and that initiating a fracture in this layer remains difficult. On Becker Peak tests on the weak layer showed that even if this layer breaks, the resulting fracture should not travel very far (snowpit). On Stevens Peak similar tests still indicated that if a fracture started, it would likely propagate through the weak layer (video). So far out of 14 observations concerning this weak layer since March 18th, only two others have shown results like those seen on Becker yesterday. All of the other 11, have indicated that fracture propagation remains likely on this deeply buried layer.

On the surface very small wind slabs that only extended a few feet away from ridgelines and only measured four to eight inches in depth had formed on Anderson Ridge (video), Becker Peak (photos), and Stevens Peak (more info) yesterday. In the Bear Valley area where more snow fell these slabs grew slightly larger reaching up to one foot in depth in the most heavily wind loaded areas. In most places only minor skier-triggered cracking (less than a foot away from the skis) occurred, and observations indicated good bonding between the old crusts and the new snow. Some sluffing and slightly larger cracking indicating more marginal bonding did occur on steep wind loaded test slopes on Becker Peak (photos). Underneath this new snow a frozen supportable crust existed in all areas on all aspects.

Today's Primary Avalanche Concern: Wind Slabs

Even though the small wind slabs that formed yesterday and last night seem to have bonded to the crusts  underneath them, some of these slabs may still react to the weight of a person on top of them today. Any of these slabs that do fail should not entrain enough snow to bury a person due to their small size and shallowness. These small slides could knock a person off balance or push them into a terrain trap that could magnify the consequences of such a slide. Pockets where these kind of instabilities could occur today will remain on the most heavily wind loaded N-NE-E aspects and cross-loaded SE aspects in isolated areas in some near and above treeline terrain. Areas south of Echo Summit could hold larger wind slabs due to more snow accumulation in those areas.

Today's Secondary Avalanche Concern: Persistent Deep Slabs

The persistent weak layer still exists and still warrants concern in most areas. Fortunately transmitting enough force through the snowpack to trigger a deep slab avalanche remains very difficult due to the depth of the weak layer and the strength of the slab above it. Tests indicate that large destructive avalanches with serious consequences could still result if that layer does start to fracture. 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 layer 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 or other avalanches could also produce these deep slab avalanches.

The bottom line:

On slopes 35 degrees and steeper, pockets of MODERATE avalanche danger exist both above and below treeline on NW-N-NE aspects and on near and above treeline E-SE aspects due to ongoing persistent deep slab instability and some new shallow wind slabs. Large destructive deep slab avalanches remain possible. For all other areas, avalanche danger is generally LOW.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	17-25 deg. F.
Max. temperature in the last 24 hours:	29-36 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	20 mph
Maximum wind gust in the last 24 hours:	65 mph
New snowfall in the last 24 hours:	North of Echo Summit: 1-4 inches | South of Echo Summit: 3-7 inches
Total snow depth:	42-77 inches

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

For 7000-8000 ft:
	Monday:	Monday Night:	Tuesday:
Weather:	Mostly cloudy with scattered snow showers.	Cloudy with isolated snow showers in the evening. Slight chance of snow showers after midnight.	Cloudy with a slight chance of snow.
Temperatures:	30-38 deg. F.	18-25 deg. F.	38-46 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	10-15 mph with gusts to 25 mph	15-20 mph with gusts to 35 mph	20-30 mph with gusts to 45 mph
Expected snowfall:	up to 1 in.	O in.	O in.
For 8000-9000 ft:
	Monday:	Monday Night:	Tuesday:
Weather:	Mostly cloudy with scattered snow showers.	Cloudy with isolated snow showers in the evening. Slight chance of snow showers after midnight.	Cloudy with a slight chance of snow.
Temperatures:	27-33 deg. F.	16-23 deg. F.	33-39 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	20-30 mph with gusts to 45 mph	30-40 mph with gusts to 50 mph increasing to 60 mph after midnight	35-45 mph with gusts to 70 mph
Expected snowfall:	up to 1 in.	O in.	O in.