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.

So far 1.5 to 2 inches of precipitation has fallen across the forecast area. With snow levels fluctuating between 6500 ft. and 7200 ft. yesterday, most of this precipitation fell as rain below 7200 ft. Temperatures started to cool this morning after 1-2am causing snow levels to start falling. By daybreak snow levels should fall to between 5000 ft. and 5500 ft. Above 7200 ft., 10-16 inches of heavy, new snow has fallen during this storm. A few more inches of snow should accumulate today before a high-pressure ridge pushes the storm out of the area. The winds, which have been averaging almost 50 mph over the Sierra Crest, should start to decrease today as the high-pressure ridge builds. Tonight the ridge should cause the winds to start shifting to the east and northeast. These easterly winds should continue through tomorrow. This ridge should also bring clearing skies over the next 36 hours.

Observations:

Observations from the Mt. Rose area and near Mt. Lola along the Sierra Crest both showed between 10 and 14 inches of new snow in wind-loaded areas near and above treeline yesterday. The strong southwest winds transported significant amounts of snow in both of these areas forming wind-slabs on leeward slopes. Layer bonding tests in both areas showed that the new snow had started to bond to the old snow surfaces. However, several weaknesses exist in the new snow. In the Mt. Lola area the new snow was upside-down with a heavier, wind-slab layer sitting on top of a softer, lighter layer from earlier in the storm. Observations revealed some shooting cracks within the new snow in both these areas yesterday. In the Mt. Lola area large, tender cornices had formed above wind-loaded slopes by 1pm. Skiers could easily break off refrigerator sized pieces of these cornices. Snowpit tests in the Mt. Lola area showed that the Oct. 19th facet layer still exists in this area. It buried about 4-5 ft down near the bottom of the snowpack. These tests indicate that in the unlikely event that this layer breaks, the fracture could still propagate through the snowpack along this layer in this area. 

Avalanche concern #1:

Newly formedwind-slabs on wind-loaded N-NE-E aspects near and above treeline will comprise today's primary avalanche concern. These wind-slabs started to crack and break yesterday afternoon. Overnight the southwest winds and more snow caused these slabs to increase in size. Human-triggering of avalanches involving these new wind-slabs will be likely today. Avalanches involving these wind-slabs could be 2-4 ft deep with even deeper slabs forming in the most heavily wind-loaded areas. Use clues like cornices, blowing snow, drifts, ripples and other wind created features to determine which slopes have been wind-loaded.

Avalanche concern #2:

Avalanches resulting from weaknesses within the new snow layers are the second avalanche concern today. The shifting winds and fluctuating temperatures have caused several different layers to form within the new snow. In some areas these layers have not fully bonded to each other. Human triggering of avalanches resulting from failure between the new layers in the storm snow will be possible. Snowpack failure could occur just above the old/new snow interface and possibly just below the old, surface crusts where a small layer of weak sugary crystals exists. Steep slopes above 7200 ft. will hold the best potential for this kind of avalanche activity. This instability should dissipate quickly as the storm snow settles and bonds to itself.

Deep slab avalanches resulting from failure of the Oct. 19th facet layer remain unlikely but not impossible today.

The bottom line:

Near and above treeline CONSIDERABLE avalanche danger exits on wind-loaded N-NE-E aspects 35 degrees and steeper. Human triggered avalanches will be likely on these slopes. MODERATE avalanche danger exists on all other aspects at all elevations on slopes steeper than 35 degrees. Human triggered avalanches will be possible on any steep slopes today.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	26 deg. F.
Max. temperature in the last 24 hours:	30 deg. F.
Average wind direction during the last 24 hours:	South southwest
Average wind speed during the last 24 hours:	48 mph
Maximum wind gust in the last 24 hours:	99 mph
New snowfall in the last 24 hours:	10-15 inches
Total snow depth:	50-71 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 snow showers throughout the day.Snow level should lower to around 5000-5500 ft.	Partly cloudy with isolated snow showers in the evening. Clearing after midnight.	Partly cloudy
Temperatures:	25-32 deg. F.	17-25 deg. F.	33-40 deg. F.
Wind direction:	Southwest shifting to west	West shifting to the northeast after midnight	East
Wind speed:	15-25 mph with gusts to 35 mph decreasing to 10-15 mph with gusts to 25 mph this afternoon	10 mph	10 mph
Expected snowfall:	up to 2 in.	O in.	O in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Mostly cloudy with snow showers throughout the day.	Partly cloudy with isolated snow showers in the evening. Clearing after midnight.	Partly cloudy
Temperatures:	24-30 deg. F.	18-24 deg. F.	33-40 deg. F.
Wind direction:	Southwest shifting to west	Northwest shifting to northeast	Northeast
Wind speed:	30-45 mph with gusts to 75 mph decreasing to 25-35 mph with gusts to 55 mph in the afternoon	15-25 mph with gusts to 50 mph	10-20 mph with gusts to 40 mph decreasing to 30 mph in the afternoon
Expected snowfall:	up to 3 in.	O in.	O in.