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 low pressure system near the CA coast should continue to push warmer air and clouds into the region today and tomorrow. The southwest flow caused by this system should keep the moderate southwest winds blowing across the forecast area as well. Most of the moisture associated with this system should stay north of the region; however, some snow showers could develop over the area during the next 24 hours. As the low moves farther east tomorrow, expect cloud cover, southwest winds, and the chances for snow showers to increase. Even though some snow showers may occur, the forecast calls for little to no accumulation.

Observations:

Skiers triggered a small (30 ft wide, less than 1ft in depth) soft slab avalanche on Echo Peak yesterday on a 40 degree, NE facing slope. The first skier down the slope triggered the largest part of the slab; however, enough hangfire remained for the second skier to trigger a smaller part of the slab. The avalanche did not catch or carry either skier. The party reported that if they had been caught and carried any distance, the slide would have swept them into trees and rocks (more info).

Layer bonding tests and snowpit data in the Twin Peaks area (south of Alpine Meadows) yesterday showed that the snowpack continues to gain strength. Ski cuts on most 35-40 degree, N-NE-E-SE-S facing, wind-loaded and non-wind-loaded test slopes did not result in any cracking or failure. Observations also indicated that the weak layer near the bottom of the snowpack has started to form bonds within itself and with the layers above it. Some surface hoar had formed in the basins in this area, but it did not extend up onto the nearby slopes. 

Avalanche Concern #1: Lingering Storm Snow Weaknesses

As the bonds between the Nov. 28th snow and the old snow surface continue to gain strength, areas where human-triggered avalanches remain possible will grow more and more isolated. However, some of these isolated pockets of instability do still exist as evidenced by continued reports of human-triggered avalanches. The most likely places for these isolated pockets of instability will be in more complex terrain (steep couloirs, hanging snowfields, unsupported slopes, heavily wind-loaded areas etc) on N-NE-E facing slopes steeper than 37 degrees. Most of these avalanches should remain small only involving the Nov 28th snow, but even small avalanches can have serious consequences especially in complex terrain.

Avalanche Concern #2: Deep Slabs

Avalanches resulting from the failure of the Nov 9th facet layer (weak, sugary snow) near the bottom of the snowpack remain possible in very isolated areas where this layer remains weak. These types of avalanches should be difficult to trigger unless a person finds the exact right spot on a slope where this layer exists. Any avalanches resulting from failures of this layer would be large, deep, and dangerous. Recent observations across the forecast area suggest that this layer only remains weak in a few isolated places where a shallower snowpack exists on near and below treeline N-NE aspects that are sheltered from the east winds and had snow on them in early November. Observers have only found this persistent weak layer in the the Mt. Rose area so far.

The bottom line:

Isolated pockets of MODERATE avalanche danger exist on N-NE-E aspects 37 degrees and steeper near and above treeline. Below treeline very isolated pockets of MODERATE avalanche danger exist on N-NE aspects on slopes 35 degrees and steeper where a persistent weak layer exists near the base of the snowpack.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	27 deg. F.
Max. temperature in the last 24 hours:	34 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	30 mph
Maximum wind gust in the last 24 hours:	57 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	43-54 inches

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

For 7000-8000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Mostly cloudy with a slight chance of snow showers.	Mostly cloudy with a slight chance of snow showers.	Mostly cloudy becoming cloudy with a slight chance of snow showers.
Temperatures:	32-39 deg. F.	23-31 deg. F.	34-41 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	10-15 mph with gusts to 30 mph	10-15 mph	10-20 mph with gusts to 35 mph
Expected snowfall:	0-1/4 in.	0-1/4 in.	0-1/4 in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Mostly cloudy with a slight chance of snow showers.	Mostly cloudy with a slight chance of snow showers.	Mostly cloudy becoming cloudy with a slight chance of snow showers.
Temperatures:	29-34 deg. F.	25-31 deg. F.	30-36 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	20-30 mph with gusts to 50 mph	20-30 mph with gusts to 50 mph after midnight	25-40 mph with gusts to 50 mph increasing to 65 mph in the afternoon
Expected snowfall:	0-1/4 in.	0-1/4 in.	0-1/4 in.