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 forecast calls for a low pressure system moving from the north to the south to pass through the region over the next 36 hours. The winds have shifted to the southwest and increased ahead of this storm. Temperatures should start to fall during the day as this system approaches. Over the next 36 hours the forecast calls for 7-15 in. of snow above 8000 ft. and 5-12 in. between 7000 and 8000 ft. At lake level expect 4-8 in. Most of the snow should fall overnight tonight with only a few inches of accumulation this afternoon. The winds should shift to the north and east tonight as the storm moves south.

Observations from across the forecast area continue to indicate that the Oct. 19th facet layer remains fragile. Human-triggered whumpfing, snowpack collapse, and shooting cracks have all occurred on this layer across the forecast area this week. Several human-triggered avalanches occurred due to failure of this layer last weekend. Layer bonding tests continue to indicate that this layer can and will fail in response to a person's weight on top of the snowpack. On many NW-N-NE aspects above 8700 ft. this weak layer sits on top of a 3-12 inch thick ice layer. This ice layer provides a bed surface for avalanches to slide on after the weak layer breaks. Unfortunately, this fragile combination exists on the slopes with the most snow on them making the best places for recreation the same places where the weakest snowpack exists.

Today, this combination of the weak layer (the facets) and a slippery bed surface (the ice layer) will comprise the primary avalanche concern. In areas where this combination exists with any sort of slab on top of it human-triggered avalanches will remain possible. New snowfall and wind-loading on the NW-N-NE aspects during this storm will cause new wind slabs to form on top of the already fragile snowpack. These conditions will cause the avalanche danger to increase quickly during this storm. Human-triggerable avalanche activity will remain possible and should become more widespread and larger later this afternoon and overnight. Natural avalanche activity may become possible overnight tonight due to this new loading.

The bottom line:

Areas of MODERATE avalanche danger exist above 8,700' on NW-N-NE aspects 32 degrees and steeper both above and below treeline. For all other areas, avalanche danger is LOW. Expect the avalanche danger to increase quickly this afternoon and overnight during the storm.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	32 deg. F.
Max. temperature in the last 24 hours:	43 deg. F.
Average wind direction during the last 24 hours:	West Southwest
Average wind speed during the last 24 hours:	40 mph
Maximum wind gust in the last 24 hours:	67 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	4 to 20 inches

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

For 7000-8000 ft:
	Friday:	Friday Night:	Saturday:
Weather:	Chance of snow in the morning north of I80. Snow showers should increase and move south through the day.	Occasional snow.	Snow showers likely in the morning mostly south of I80.
Temperatures:	Midday temperatures: 34-41 deg. F. This afternoon they should drop to 30 deg. F.	18-22 deg. F.	25-30 deg. F.
Wind direction:	Southwest	North shifting to the Northeast after midnight	Northeast
Wind speed:	10-20 mph with gusts to 40 mph	10-15 mph increasing to 10-20 mph with gusts to 35 mph after midnight	10-20 mph with gusts to 40 mph
Expected snowfall:	North of I80: 2-3 in. South of I80 1-2 in.	4-7 in.	up to 2 in.
For 8000-9000 ft:
	Friday:	Friday Night:	Saturday:
Weather:	Chance of snow in the morning north of I80. Snow showers should increase and move south through the day.	Snow.	Snow showers likely in the morning mostly south of I80.
Temperatures:	30-35 deg. F. dropping in the afternoon to 18-22 deg. F.	15-20 deg. F.	22-27 deg. F.
Wind direction:	Southwest	Southwest shifting to Northeast after midnight	Northeast
Wind speed:	30-40 mph with gusts to 80 mph decreasing to 20-30 mph with gusts to 60 mph in the afternoon	20-30 mph with gusts to 50 mph increasing to 30-40 mph with gusts to 65 mph	30-45 mph with gusts to 75 mph
Expected snowfall:	2-4 in. north of I80. South of I80 1-2 in.	5-9 in.	up to 2 in.