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.

This storm brought 6-13 inches of heavy, wet snow (15-20% density in most areas) to the Central Sierra over the last 18 hrs. Most areas along the Sierra Crest received 6-10 inches of new snow. In Mt. Rose area, remote sensors indicated 10-13 inches new snow. The southwest winds remained strong overnight averaging between 35 and 45 mph. The forecast calls for wind and snow to continue today with another 2-6 inches of snow possible above 7000'. After hovering between 6000' and 6500' last night snow levels should fall to below 6000' today. By tonight the snowfall should taper off and the winds should start to decrease as this system moves out of the area. The forecast calls for a break in the weather tomorrow before another winter storm impacts the region starting Friday.

Observations:

Yesterday observations in the Mt. Rose backcountry and on Carpenter Peak (north of Castle Peak) showed that the southwest winds had already started forming stiff, reactive wind-slabs near ridgelines before the new snow started falling. Several wind-loaded, N-E-facing, 35-38-degree test-slopes failed in response to ski-cuts in both areas yesterday. On Carpenter Peak, these wind-slabs had reached 1-3 inches in depth by midday. On the east ridge of Tamarack Peak in the Mt. Rose area, the wind-slabs had grown to 6-8 inches deep by 3pm (photos and videos). These wind-slabs formed on top of softer, unconsolidated, recent snow (snowpit). Snowpit observations in both areas showed that a variety of possible weak layers ranging from thin, breakable crusts to hard, refrozen crusts to graupel to isolated areas of surface hoar exists at the base of the Feb 21st storm. In some areas that snow has bonded well to the old snow surfaces, and in others it has not. The strength of this interface remains variable across the forecast area.

Avalanche Concern #1:

The wind-slabs that have formed over the last 24 hours will comprise the primary avalanche concern today. The southwest winds started to build these new wind-slabs yesterday. As more new snow fell last night and the winds continued, these slabs grew more widespread, deeper, and heavier. These wind-slabs started to react to the weight of a skier yesterday. Human-triggered avalanche activity involving these newly-formed wind-slabs will remain probable today. Even though the best window for natural avalanches would have occurred early this morning, some natural avalanches involving these wind-slabs could still be possible on the most heavily wind-loaded slopes today.

Avalanche Concern #2:

As the snow fell last night, temperatures increased causing a layer of heavy, wet snow to accumulate on top of a layer of lighter, colder snow. This heavy layer on top of a lighter layer created an upside-down snowpack. Today, adding a person on top of the heavy, wet snow on the surface could overload the lighter snow layer below resulting in avalanche activity. These types avalanches will be possible on slopes steeper than 35 degrees where this upside-down snowpack exists.

Avalanche Concern #3:

Human-triggering of deeper avalanche activity will also remain possible today on slopes where weak layers exist near the base of the Feb. 21st snowfall. The location, strength, and distribution of these weak layers varies greatly across the forecast area. Digging quick hand pits down to the older snow and testing the bonding between the older snow surfaces and the more recent snow can help determine where these weaknesses exist.

The bottom line:

Near and above treeline on slopes 35 degrees and steeper, pockets of CONSIDERABLE danger exist on wind-loaded N-NE-E aspects and on cross-loaded NW and SE aspects. MODERATE avalanche danger exists on all other slopes steeper than 35 degrees.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	26-29 deg. F.
Max. temperature in the last 24 hours:	28-31 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	35-45 mph
Maximum wind gust in the last 24 hours:	83 mph
New snowfall in the last 24 hours:	6-13 inches
Total snow depth:	74-113 inches

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

For 7000-8000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Snow showers. Snow level dropping to below 6000 ft.	Cloudy with a 30% chance of snow.	Mostly cloudy
Temperatures:	27-34 deg. F.	19-26 deg. F.	31-38 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	15-25 mph with gusts to 50 mph	15-25 mph with gusts to 40 mph decreasing to 10-15 mph with gusts to 30 mph after midnight	10-15 mph with gusts to 25 mph
Expected snowfall:	2-4 in.	trace in.	O in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Snow showers	Cloudy with a 30% chance of snow.	Mostly cloudy
Temperatures:	27-33 deg. F.	21-27 deg. F.	27-34 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	30-45 mph with gusts to 75 mph decreasing to 20-35 mph with gusts to 60 mph this afternoon	20-30 mph with gusts to 45 mph	20-30 mph with gusts to 45 mph
Expected snowfall:	2-6 in.	trace in.	O in.