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.

A low pressure system combined with warm subtropical moisture should bring rain and high elevation snow to the forecast area through Monday morning. After a brief period of lower snow levels this morning, the snow level should rise and remain between 7500' and 8000' for most of the storm. The forecast calls for .5 to 1 inch of water to fall in some form above 7000' along the Sierra Crest today. Moderate to strong southwest winds will accompany this storm.

Yesterday observers reported no new avalanches; however, large areas collapsed and whumphed on low angle (25-27 degree), N-NE facing slopes in the Cascade Creek area between 7200' and 7600'. Layer bonding tests showed this collapse occurred on the weak faceted snow grains between the late January crusts and the February snow. Observations from across the forecast area over the last few days show that this faceted layer remains weak. It can barely support the snow on top of it in many areas.

This layer of weak facets will continue to comprise the primary avalanche concern today. In areas where this layer exists, the snowpack may not be able to handle the new loading that occurs today. Most of this loading will come in the form of rain below 8000'. The rain will do 3 things to make the snowpack weaker. 1. It adds weight to the snow without adding any strength. 2. It dissolves the bonds that hold the snowpack together. 3. It lubricates the layers that could serve as bed surfaces. The .5-1 inch of new rain and 4-8 inches of new snow forecasted should overwhelm the weak facets at the base of the February snow making natural and human-triggered avalanche activity likely on NW-N-NE aspects below 8700' where these facets exist.

Today's second avalanche concern will be rain on new snow below 8000'. Observations this morning show that 1-2 inches of snow has fallen in some areas below 8000'. As the freezing level fluctuates during this storm snow could easily change to rain. This rain would cause instability in any new snow that it falls on top of and could result in avalanche activity. If enough new snow accumulates before the rain falls on top of it this avalanche activity could be large enough to bury a person. The most likely places for larger amounts of snow to accumulate will be the wind-loaded slopes on the N-NE-E aspects.

This wind loading brings up the third avalanche concern today: new wind slabs. These new wind slabs should form due to the new snow and wind forecasted for today. They should be sensitive to human triggers and cornice failures. These slabs will be largest and most dangerous on wind loaded N-NE-E aspects near and above treeline.

With so many different avalanche concerns and conditions, it will be hard to travel safely in the backcountry today without expert skills in backcountry travel techniques, terrain evaluation, and snowpack evaluation.

The bottom line:

On slopes steeper than 35 degrees, the avalanche danger is HIGH on NW-N-NE aspects with pockets of HIGH danger on E aspects below 8700'.  On the SE-S-SW-W aspects that receive rain today the avalanche danger is CONSIDERABLE. Above 8700' the avalanche danger is CONSIDERABLE on N-NE-E aspects on slopes steeper than 35 degrees and MODERATE on other aspects.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	30 deg. F.
Max. temperature in the last 24 hours:	38 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	38 mph
Maximum wind gust in the last 24 hours:	75 mph
New snowfall in the last 24 hours:	0-1 inches
Total snow depth:	110 inches

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

For 7000-8000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:	Snow and rain. Snow level between 7500 and 8000 ft.	Snow and rain. Snow level between 7000 and 7500 ft.	Snow and rain in the morning with snow level between 7000 and 7500 ft. Precipitation should taper off in the afternoon with skies becoming mostly cloudy.
Temperatures:	32-40 deg. F.	29-34 deg. F.	34-40 deg. F.
Wind direction:	Southwest	South	Southwest
Wind speed:	15-25 mph with gusts to 40 mph	15-25 mph with gusts to 35 mph	15-25 mph with gusts to 35 mph
Expected snowfall:	3-8 in.	3-8 in.	3-6 in.
For 8000-9000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:	Mostly snow. Snow level between 7500-8000 ft.	Snow	Snow in the morning becoming mostly cloudy in the afternoon
Temperatures:	28-32 deg. F.	23-29 deg. F.	32-36 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	25-40 mph with gusts to 75 mph	25-40 mph with gusts to 75 mph	25-40 mph with gusts to 80 mph
Expected snowfall:	4-8 in.	4-8 in.	3-6 in.