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 continues to build over the forecast area. A weather system passing just to the north of the forecast area will bring increasing cloud cover this afternoon. Remote sensors are reporting air temperatures above 8,000' in the low to mid 30s this morning. Maximum daytime air temperatures for areas above 7,000' are expected to reach the low 40s to mid 50s today. Ridgetop winds are out of the southwest this morning and are light in speed. Winds are forecast to shift to the west and become light to moderate in speed this afternoon. Partly to mostly cloudy skies, well above freezing air temperatures, and light to moderate southwest winds are forecast for tomorrow.

Recent Observations:

Yesterday, a skier triggered wet loose snow avalanche occurred on Flagpole Peak (Echo Summit area) in below treeline terrain on a ENE aspect 40 degree slope around 10am. This avalanche began as a point release, widening to 150 feet and traveled 1000 ft down slope. The avalanche failed on wet snow in the very top portion of the snowpack, but then entrained snow down to the upper most melt freeze crust at the base of the recent storm snow. Prior to the avalanche occurrence, snowpit data collected on the edge of the area where the avalanche occurred indicated mixed stability results (photos, more info).

Nearby on Powderhouse Peak (Luther Pass area), snowpit data and informal observations made on N to NE aspects indicated a stable snowpack in areas where skier triggered slab avalanche activity occurred on April 13 (pit profile, photos, more info). The biggest difference between these two areas is the more easterly aspect component and significant sun exposure due to few trees on Flagpole Peak. The areas observed on Powderhouse Peak have a much more northerly aspect component, significantly more shade, and more indirect sun exposure.

Today's Primary Avalanche Concern: Wet snow

Near to above freezing air temperatures last night and some cloud cover is expected to have allowed for a poor to marginal overnight refreeze of wet surface snow. Areas of wet snow instability are expected to quickly become widespread today on all aspects at most elevations. Roller balls, wet loose snow avalanches, and wet slab avalanches are possible in sun exposed areas. By mid morning, wet snow is expected to become widespread in sun exposed areas and will also form on northerly aspects that receive fairly direct sun exposure under high sun angles this time of year. Any areas where storm and wind slab instability lingers from the most recent storm event may allow for wet slab avalanches to occur up to 2 feet deep in the snowpack.

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 could occur within the next few weeks.

The bottom line:

Both above and below treeline widespread MODERATE avalanche danger will form quickly today on all aspects on slopes 35 degrees and steeper in response to daytime warming.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	31 to 36 deg. F.
Max. temperature in the last 24 hours:	35 to 44 deg. F.
Average wind direction during the last 24 hours:	West
Average wind speed during the last 24 hours:	12 mph
Maximum wind gust in the last 24 hours:	27 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	42 to 96 inches

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

For 7000-8000 ft:
	Monday:	Monday Night:	Tuesday:
Weather:	Mostly cloudy skies.	Mostly cloudy skies, becoming partly cloudy.	Partly cloudy skies, becoming mostly cloudy.
Temperatures:	48 to 54 deg. F.	27 to 34 deg. F.	48 to 54 deg. F.
Wind direction:	W	SW	SW
Wind speed:	Light winds becoming 10 to 15 mph with gusts to 25 mph in the afternoon.	5 to 15 mph.	Light winds becoming 15 to 20 mph with gusts to 30 mph in the afternoon.
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Monday:	Monday Night:	Tuesday:
Weather:	Mostly cloudy skies.	Mostly cloudy skies, becoming partly cloudy.	Partly cloudy skies, becoming mostly cloudy.
Temperatures:	40 to 47 deg. F.	28 to 36 deg. F.	40 to 47 deg. F.
Wind direction:	W	SW	SW
Wind speed:	Light winds becoming 15 to 25 mph with gusts to 35 mph in the afternoon.	15 to 25 mph with gusts to 40 mph.	10 to 15 mph with gusts to 25 mph, increasing to 15 to 25 mph with gusts to 40 mph.
Expected snowfall:	O in.	O in.	O in.