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.

High pressure is building over the forecast area. Lingering mid level clouds are expected to move out of the forecast area this morning. Shortly thereafter thin high cloud cover will spread over the region, but still allow for plenty of sunshine. Remote sensors are reporting air temperatures above 8,000' in the 20s this morning. Maximum daytime air temperatures for areas above 7,000' are expected to reach the upper 30s to low 50s today. Ridgetop winds remain out of the northeast this morning and are light in speed. Winds are forecast to shift to the west and become light to moderate in speed as the day progresses. Another round of sunny skies, well above freezing air temperatures, and light to moderate west winds are forecast for tomorrow.

Recent Observations:

Yesterday, snowpack stability took on the trend of variability across the forecast area as expected. Wind and storm slabs that formed over the past several days were unstable in some areas and stable in other areas. On Talking Mountain (Echo Summit area) two skier triggered avalanches occurred below treeline on a NE aspect at around 8,000' and 7,700'. Both of these avalanches were triggered on recently wind loaded slopes with 40 degree slope angle convex roll over trigger points. Both avalanches failed 2 feet deep in the snowpack and were reported at 30 feet wide and traveled 200 feet down slope (more info). Nearby on Echo Peak, informal observations and formal snowpit data collected on a N aspect near 7,300' indicated stable snowpack conditions. Very minor wet snow instability in the form of roller balls off of rocks in sun exposed areas were observed as the sun broke through the clouds for a few hours mid day (pit profile, photos, more info).

On Mt. Tallac (Desolation Wilderness area), hand pits and hand shears along the skin track on the NE ridge showed a density inversion just above the old melt freeze crust at the base of the recent storm snow. Ski cutting above the skin track produced no snowpack failure. Recent storm snow amounts on top of the crust ranged from 8 inches below 8,000' to 1 to 2 feet between 8,000' and the ridgetop at 9,100'. Ski cuts along a wind loaded NE aspect convex roll over just below the ridgeline produced no results. Snowpit data collected at 9,100' on a NE aspect revealed a difficult to trigger density inversion at the base of the recent storm snow that remained capable of propagation that could contribute to a slab avalanche (pit profile, more info).

On Castle Peak (Donner Summit area) north winds were scouring snow from above treeline terrain on northerly aspects. Varying surface wind slab densities were noted with generally wind affected snow on most aspects above treeline. Deep deposits of recent storm snow remained present on terrain features in protected pockets. No slab movement, shooting cracks, or other evidence of instability was caused by either skier weight or ski cutting (more info).

Today's Primary Avalanche Concern: Wet snow

Areas of wet snow instability are expected to become widespread today at most elevations on E-SE-S-SW-W aspects. Roller balls, wet loose snow avalanches, and shallow wet slab avalanches are possible in sun exposed areas. As the day progresses wet snow is expected to become widespread in sun exposed areas and may also form in more isolated areas on northerly aspects that receive less direct sun exposure. Recently cross loaded SE aspect gullies are the most likely areas for a wet slab avalanche to occur.

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

The continued lingering of isolated pockets of unstable wind slabs and storm slabs is expected today as a density inversion near the base of the recent storm snow continues to hold some of the necessary characteristics to contribute to human triggered slab avalanches. Areas of instability are once again expected to exist in pockets both above and below treeline. The largest wind slabs capable of contributing to larger human triggered avalanches are expected on NW-N-NE aspects. As a continuation of the variance in snowpack stability observed across the area yesterday, expect to find areas of instability existing within surrounding areas of seemingly stable snow. A slope by slope approach to snowpack stability assessment remains worthwhile today due to the expected variability.

Other things to think about: The Persistent Weak Layer

Due to the depth of the persistent weak layer (5 to 8 ft down) and the strength of the snow above it, triggering a deep slab avalanche on NW-N-NE aspects has become unlikely. At this time data indicates that collapsing this layer would require an extremely large trigger or significant weakening of the snowpack. Spring melting could eventually allow free water to percolate down through the snowpack and cause sufficient weakening of this layer for a deep wet slab avalanche cycle to occur. Conditions that would create enough melting for this scenario remain several weeks to a month or more away.

The bottom line:

Both above and below treeline widespread MODERATE avalanche danger will form on E-SE-S-SW-W aspects on slopes 35 degrees and steeper in response to daytime warming. On NW-N-NE aspects, avalanche danger is LOW with pockets of MODERATE danger in wind loaded areas both above and below treeline on slopes 35 degrees and steeper. Areas of unstable snow will exist within surrounding areas of seemingly stable snow.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	21 to 27 deg. F.
Max. temperature in the last 24 hours:	29 to 36 deg. F.
Average wind direction during the last 24 hours:	Northeast
Average wind speed during the last 24 hours:	15 mph
Maximum wind gust in the last 24 hours:	35 mph
New snowfall in the last 24 hours:	0 to trace inches
Total snow depth:	43 to 100 inches

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

For 7000-8000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:	Partly cloudy skies. Thin high cloud cover.	Partly cloudy skies. Thin high cloud cover.	Mostly cloudy skies. Thin high cloud cover.
Temperatures:	45 to 51 deg. F.	26 to 38 deg. F.	47 to 54 deg. F.
Wind direction:	W	W	W
Wind speed:	5 to 15 mph.	5 to 15 mph.	5 to 15 mph.
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:	Partly cloudy skies. Thin high cloud cover.	Partly cloudy skies. Thin high cloud cover.	Mostly cloudy skies. Thin high cloud cover.
Temperatures:	38 to 46 deg. F.	27 to 35 deg. F.	40 to 47 deg. F.
Wind direction:	W	W	W
Wind speed:	15 to 20 mph with gusts to 35 mph.	15 to 20 mph with gusts to 30 mph.	15 to 25 mph with gusts to 35 mph.
Expected snowfall:	O in.	O in.	O in.