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.

The southwest winds have increased significantly over the last 24 hours and should remain strong as a series of storms begins to impact the forecast area. These winds and storms should also bring warmer air into the region with today's highs about 10 degrees warmer than yesterday's. Precipitation due to the first of the storm systems should remain mostly north of the forecast area with only scattered snow showers developing around the region today and tonight. The forecast calls for another storm system to arrive tomorrow afternoon bringing even stronger southwest winds, warmer temperatures, and more significant precipitation. Snow levels with Thursday's system should remain between 6500 ft and 7500 ft allowing some of this precipitation to fall as rain below 7500 ft. Above 7500 ft the forecast area could see 2-6 inches of snow tomorrow afternoon. Click here for a more detailed online weather briefing from the Reno NWS. 

Observations:

Across the forecast area the snowpack remains patchy with snow coverage limited to the NW-N-NE-E aspects. In the southern part of the forecast area and in areas east of Lake Tahoe a very shallow and inconsistent snowpack exists due to significant wind scouring earlier this season. If a snowpack still exists in these areas, it consists of a mix of weak sugary snow with a few small hard slabs on top of it in isolated areas and hard icy snow left over from last winter. Farther north along the Sierra Crest a deeper snowpack exists on the northerly aspects. In these areas rain and warmer weather formed strong frozen crusts on the snow surface in most places. As colder weather returned weak faceted snow reformed both above and below these crusts. Areas where strong melt-freeze conditions exist throughout the entire snowpack have become increasingly isolated. Yesterday on Castle Peak similar conditions existed with a thick strong crust near the surface surrounded by faceted snow (snowpit and video).

Avalanche Concerns:

The snowfall expect to occur today should not add enough load to the current snowpack for the avalanche danger to increase above LOW today. Where the deepest snowpack exists, strong crusts continue to hold the snowpack together and prevent the weak snow below them from collapsing when weighted. In areas where a thinner weaker crust exists, it remains weak enough that it falls apart before fractures in the weak layer below it travel very far. Significant anchors remain on the slopes where a more shallow snowpack exists. These anchors disrupt the existing weak layers and help hold the snowpack in place. Finding areas where a slab, weak layer, and bed surface all exist together on one slope has become more and more difficult. 

As more storms bring more precipitation and wind later this week the avalanche danger will increase. New slabs will form on the on top of the thin layer of weak snow that exists on top of the existing crusts. This combination will provide the necessary ingredients for avalanche activity. The crusts will serve as great bed surfaces, the thin layer of weak snow as a weak layer, and the new snow could form a slab. Rain or enough new loading during these storms could also weaken the crusts enough for avalanche activity to begin including snow underneath the crusts. Cautious travel habits and careful snowpack evaluation in the backcountry during this storm cycle can help prevent people from being involved in dangerous avalanches.

The bottom line:

Avalanche danger remains LOW for all elevations and aspects. Continue to use normal caution in the backcountry. As winter storms impact the forecast area later this week, the avalanche danger will increase.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	20-28 deg. F.
Max. temperature in the last 24 hours:	22-31 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	Along the Sierra Crest: 40 mph - In the Mt Rose area: 48 mph
Maximum wind gust in the last 24 hours:	Along the Sierra Crest: 60 mph - In the Mt Rose area: 109 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	0-18 inches

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

For 7000-8000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Cloudy with a slight chance of snow near the Sierra Crest	Cloudy with a slight chance of snow near the Sierra Crest	Cloudy with a mix of snow and rain developing in the afternoon
Temperatures:	31-38 deg. F.	24-31 deg. F.	34-41 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	25-40 mph with gusts to 60 mph	25-35 mph with gusts to 60 mph decreasing to 50 mph after midnight	25-30 mph with gusts to 45 mph increasing to 40-45 mph with gusts to 75 mph in the afternoon
Expected snowfall:	O in.	up to 1 in.	2-4 in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Cloudy with a slight chance of snow near the Sierra Crest	Cloudy with a slight chance of snow near the Sierra Crest	Cloudy with snow developing in the afternoon
Temperatures:	25-32 deg. F.	23-30 deg. F.	35-41 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	55-70 mph with gusts to 105 mph	55-60 mph with gusts to 100 mph decreasing to 45-50 mph with gusts to 80 mph after midnight	45-50 mph with gusts to 75 mph increasing to 70-75 mph with gusts to 120 mph in the afternoon
Expected snowfall:	O in.	up to 1 in.	2-6 in.