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 currently affecting the forecast area has brought 8 to 11 inches of new snow overnight above 8,000'. An additional 4 to 8 inches of accumulation is forecast above 7,000' prior to the end of significant snowfall which is expected to occur around 11 am. Remote sensors are reporting air temperatures above 8,000' in the mid to upper 20s this morning. Maximum daytime air temperatures above 7,000' are forecast to warm into the upper 20s to upper 30s today. Ridgetop winds remain out of the southwest this morning and are strong in speed. Winds are forecast to decrease in speed this afternoon, but will likely remain moderate to strong through this evening. For tomorrow expect a mix of sun and clouds, moderate speed southwest winds, and above freezing air temperatures.

Recent Observations:

Observations made yesterday revealed widespread wind slabs in wind loaded and cross loaded areas near and above treeline on NW-N-NE-E-SE aspects. The most unstable areas were reported south of Hwy 50 where the most new snow fell last weekend and the most snow was available yesterday for wind transport. In the Carson Pass area, wind slabs were noted to fail in response to ski cuts on slopes steeper than 40 degrees and in snowpit tests. Failure occurred around 1 foot deep in the snowpack on a layer of lower density recent storm snow, just below the base of the more dense surface wind slab (videos, more info). Much further north in the Independence Lake area, wind slabs existed, but were small, shallow and unreactive to intentional cornice collapse, ski cuts, and snowpit tests (photo, pit profile, more info). Similar stable wind slab conditions were observed in the Mount Rose area (pit profile, video, more info).

Today's Primary Avalanche Concern: Storm Slabs and Wind Slabs

Unstable wind slabs that existed yesterday in near and above treeline areas will likely linger today as storm snow is wind loaded on top of these slabs on NW-N-NE-E-SE aspects. Snowpack failure, mainly in the form of human triggered slab avalanches is expected today. With the new snow load on top of already unstable wind slabs, avalanches occurring up to 3 feet deep in the snowpack are possible, especially in areas south of Hwy 50. In areas where the wind slabs from the past two days are more stable, snowpack failure will focus on instability within the storm snow.

Today's Secondary Avalanche Concern: Persistent Deep Slabs

The persistent weak layer of old crust and faceted snow still exists above and below treeline on most NW-N-NE aspects. Since March 17th, 15 out of the 19 field observations targeting this weak layer indicate that collapse of this weak layer is still likely to cause propagating slab failure deep within the snowpack. Transmitting sufficient 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 overlying slab in most areas. Isolated areas with a comparatively shallow snowpack where this weak layer is less than 4 feet below the snow surface such as near exposed rock outcrops, cliffs, unsupported slopes, and other complex terrain features are the most likely areas to trigger failure of this weak layer. Large triggers such as cornice collapse or other avalanches could provide sufficient force to trigger a deep slab avalanche. Any deep slab avalanches that occur at this time will be large and destructive.

The bottom line:

Near and above treeline avalanche danger is CONSIDERABLE on NW-N-NE-E-SE aspects on slopes 35 degrees and steeper due to newly formed storm slabs, wind slabs, and ongoing persistent deep slab instability. Large destructive deep slab avalanches remain possible both above and below treeline on NW-N-NE aspects. For all other areas, avalanche danger is MODERATE on slopes 35 degrees and steeper.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	25 to 28 deg. F.
Max. temperature in the last 24 hours:	28 to 37 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	40 mph
Maximum wind gust in the last 24 hours:	70 mph
New snowfall in the last 24 hours:	8 to 11 inches
Total snow depth:	50 to 84 inches

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

For 7000-8000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Cloudy skies with snow in the morning. Snow showers in the afternoon.	Mostly cloudy skies with isolated snow showers in the evening.	Mostly cloudy skies.
Temperatures:	32 to 40 deg. F.	19 to 26 deg. F.	42 to 48 deg. F.
Wind direction:	SW	SW	SW
Wind speed:	25 to 35 mph with gusts to 55 mph, decreasing 15 to 25 mph with gusts to 40 mph in the afternoon.	15 to 25 mph with gusts to 35 mph.	15 to 25 mph with gusts to 35 mph.
Expected snowfall:	4 to 8 in.	0 to trace in.	O in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Cloudy skies with snow in the morning. Snow showers in the afternoon.	Mostly cloudy skies with isolated snow showers in the evening.	Mostly cloudy skies.
Temperatures:	27 to 35 deg. F.	18 to 25 deg. F.	35 to 41 deg. F.
Wind direction:	SW	SW	SW
Wind speed:	65 to 70 mph with gusts to 95 mph, decreasing to 50 to 55 mph with gusts to 80 mph in the afternoon.	35 to 45 mph with gusts to 65 mph.	30 to 40 mph with gusts to 55 mph.
Expected snowfall:	4 to 8 in.	0 to trace in.	O in.