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.

Over the last 24 hours, 15 inches of 15%-18% density snow has fallen along the Sierra Crest north of Hwy. 50. South of 50 closer to 17 inches of similar new snow has accumulated. On the east side of Lake Tahoe in the Carson Range, 11-13 inches of slightly lighter (12%-15% density) snow fell. These accumulations bring storm snow totals to 16-24 inches of new snow since Sunday. Snow showers tapered off last night and should remain scattered this morning as the first storm system leaves the area. By this afternoon snowfall should increase as a second low-pressure system impacts the forecast area. Snowfall rates could reach 2-3 inches per hour this afternoon/evening as the strongest part of this second system hits the region. This system should move east tonight giving the area another small break in the stormy weather tomorrow morning. A stronger low-pressure system arrives tomorrow bringing more intense southwest winds and more new snow for Wed. and Thurs.

Observations:

By 12 pm yesterday, shooting cracks and small, skier-triggered avalanches started occurring on wind-loaded, NW-N-NE-facing, slopes steeper than 35 degrees. Observations along Carpenter Ridge (near Independence Lake) showed rapidly-growing wind slabs that would easily break in response to the weight of a skier (photos and video). Similar conditions existed near the ridge on Talking Mountain (near Echo Summit- photos). Near Mt. Judah (Donner Summit area) observers also reported shooting cracks on a wind-loaded slope below treeline (photos). In all three of these areas the cracks and small avalanches occurred due to failure of weaknesses within the new snow a few inches above the old snow surface. Good bonding existed between the old snow surface and the new snow in all three areas.

Avalanche Concern #1:

New snow and strong south and southwest winds will bring newly formed wind slabs to the top of the avalanche concern list again today. These slabs started to react to a person's weight yesterday afternoon. With more snow and continued wind-loading by the south and southwest winds today, these slabs will grow larger and more widespread. They will become easier to trigger and natural avalanches involving these wind slabs will be possible today, especially this afternoon during the peak of today's snowfall. Human-triggered avalanches involving these wind slabs will be probable. In heavily wind-loaded areas these wind slabs could easily be 3-5 ft deep. These wind slabs will most likely exist on wind-loaded, NW-N-NE-E aspects near and above treeline. Some pockets of wind slabs could also exist in heavily wind-loaded areas below treeline.

Avalanche Concern #2:

The changing winds and fluctuating temperatures have created several different layers within the storm snow. These layers have not had time to fully bond to one another. Avalanche activity within the new snow due to weakness between the new snow layers and other storm snow weaknesses will be possible today on any open slopes steeper than 35 degrees.

Avalanche Concern #3:

Even though observations this week indicate that deep slab avalanches are unlikely, they are not impossible in very isolated areas. Deep slab instability could occur on a layer of lightly faceted snow crystals down at the level of the January 11 crust. This crust exists around 1 foot below the old/new snow interface in most areas. Observations made near Crater Lake (Carson Pass area) on Jan 16 revealed that fracture propagation was possible on this layer (pit profile). Observations made over the past 4 days in the Bear Valley, Mount Rose, and Donner Summit areas found the presence of this crust, but no evidence of instability associated with it (more info).

The bottom line:

Near and above treeline the avalanche danger is CONSIDERABLE on NW-N-NE-E aspects steeper than 35 degrees. Below treeline pockets of CONSIDERABLE danger exist on open, NW-N-NE-E aspects steeper than 35 degrees. The avalanche danger is MODERATE on all other aspects.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	22 deg. F.
Max. temperature in the last 24 hours:	28 deg. F.
Average wind direction during the last 24 hours:	Shifting between south and southwest
Average wind speed during the last 24 hours:	30-40 mph
Maximum wind gust in the last 24 hours:	90 mph
New snowfall in the last 24 hours:	15-17 inches
Total snow depth:	61-89 inches

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

For 7000-8000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Snow showers in the morning. Snow becoming widespread and heavier this afternoon and evening.	Snow showers	Snow showers in the morning. Snow should become more widespread and intense by the afternoon.
Temperatures:	22-29 deg. F.	13-20 deg. F.	21-28 deg. F.
Wind direction:	South	Southwest	South
Wind speed:	15-25 mph with gusts to 40 mph	15-25 mph decreasing to 10-15 mph with gusts to 35 mph	20-30 mph with gusts to 35 mph increasing to 45 mph in the afternoon
Expected snowfall:	5-8 in.	2-4 in.	6-10 in.
For 8000-9000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Snow showers in the morning. Snow becoming widespread and heavier this afternoon and evening.	Snow showers	Snow showers in the morning. Snow should become more widespread and intense by the afternoon.
Temperatures:	18-25 deg. F.	11-18 deg. F.	17-24 deg. F.
Wind direction:	South	Southwest	Southwest
Wind speed:	25-40 mph with gusts to 60 mph	20-35 mph with gusts to 65 mph	30-45 mph with gusts to 80 mph increasing to 40-55 mph with gusts to 90 mph
Expected snowfall:	6-10 in.	2-6 in.	6-10 in.