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.

This advisory was posted on January 13, 2008 7:00 AM
Click here for a detailed map of the SAC forecast area

2_moderate.jpg
Today's Advisory:

Avalanche danger is MODERATE for newly wind loaded SE-S-SW aspects steeper than 35 degrees at all elevations. The avalanche danger is LOW on all other aspects.

Yesterday's weak storm system ended up surprising the Mount Rose area with 2-4 inches of new snow in the morning. North of Highway 50 along the crest it left isoated areas of less than 2 inches of new snow. By the afternoon skies started clearing as a strong ridge of high pressure moved into the forecast area. Overnight temperatures started increasing at the upper elevations. Most of the remote sensors already report temperatures near or above freezing this morning. This high pressure should bring unseasonable warm temperatures to the region today and even more warming tomorrow. The winds shifted to the northwest yesterday afternoon and shifted to the northeast and east overnight. They should continue from the east today and diminish in strength by tomorrow.
Today's forecast calls for clear, sunny skies and temperatures to crest at almost 10 degrees more than yesterday's highs. This warming should lead to some wet snow instabilities in the forecast area. The initial wet snow instabilities should be limited to the surface layers of the snow. Expect to see roller balls, pinwheels, and wet point release activity today. Some wet slab activity may become possible on slopes steeper than 35 degrees. The sun and warmth will melt the bonds between the snow grains and upper layers in the snowpack causing the upper levels of the snowpack to lose strength until they refreeze overnight. Over time this melt-freeze cycle will strengthen the snowpack; however, each day during the melt phase of the cycle the snowpack will be weaker. As the free water forms in the upper snowpack it should start to establish melt water pathways down through the snowpack over the next few days. Once this happens the free water will be less likely to saturate a specific layer in the snowpack and wet slab avalanches will be less likely. The wet snow instabilities mentioned above will be most prevalent in areas that did receive new snow yesterday. This new snow has been transported onto the aspects that see the most sun (SE-S-SW) by the east winds. The rain and warmth from Friday and Saturday will help to diminish the wet slide hazard for today because they started the melt-freeze process in the old snow. The solid overnight refreeze, relatively low sun angles, shortness of the daylight hours, and east winds will also help to keep this hazard from being as widespread as it could.

Human triggered wet slab, roller balls, pinwheels, and point release avalanche activity is possible today on newly wind loaded SE-S-SW aspects that are steeper than 35 degrees. On other aspects and in areas that did not receive new snow wet snow instabilities should be limited to some small roller ball, pinwheel, and wet surface sluffs. Very isolated pockets of more significant wet snow instabilities may exist in these areas.

The bottom line: Avalanche danger is MODERATE for newly wind loaded SE-S-SW aspects steeper than 35 degrees at all elevations. The avalanche danger is LOW on all other aspects.
Please send us your snow, weather, and avalanche observations by clicking the submit observations link on our contact page.

Andy Anderson, Avalanche Forecaster

Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet): 31 deg. F
Max. temperature at Sierra Crest past 24 hours: 35 deg. F
Average wind direction at Sierra Crest past 24 hours: Northwest shifting to the East
Average wind speed at Sierra Crest past 24 hours: 20 mph
Maximum wind gust at Sierra Crest past 24 hours: 43 mph
New snow fall at 8,200 feet past 24 hours: 2-3 inches in the Mount Rose area - trace amounts elsewhere
Total snow depth at 8,200 feet: 58 inches
Mountain Weather Forecast For Today:
Sunny and much warmer.
Temperature forecast for 8,000 to 9,000 feet: 39 to 45 deg. F
Ridgetop winds forecast for the Sierra Crest: East at 15 to 20 mph with gusts to 35 mph.
Snowfall expected in the next 24 hours: 0 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, sunny and warm with daytime highs 42 to 46 deg. F. Northeast winds at 10 to 15 mph with gusts to 25 mph.

Tonight, clear skies with overnight lows 20 to 28 deg. F. East winds at 10 mph in the evening becoming light after midnight.

For Monday, sunny and warm with some clouds developing in the afternoon. Daytime highs 44 to 48 deg. F. Southwest winds at 10 mph.

Above 8000 Feet:
Today, sunny and warm with daytime highs 39 to 45 deg. F. East winds at 15 to 20 mph with gusts to 35 mph.

Tonight, clear skies with overnight lows 23 to 31 deg. F. East winds at 10 to 15 mph with gusts to 30 mph in the evening becoming light after midnight.

For Monday, sunny and warm with some clouds developing in the afternoon. Daytime highs 41 to 47 deg. F. Southwest winds at 10 to 15 mph.

The bottom line:

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	deg. F.
Max. temperature in the last 24 hours:	deg. F.
Average wind direction during the last 24 hours:
Average wind speed during the last 24 hours:	mph
Maximum wind gust in the last 24 hours:	mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	inches

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

For 7000-8000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.