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 February 12, 2008 7:00 AM
Click here for a detailed map of the SAC forecast area

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Today's Advisory:

This morning, avalanche danger is LOW for all elevations and aspects. Areas of MODERATE avalanche danger will develop at all elevations on SE-S-SW-W aspects, 35 degrees and steeper due to daytime warming.

Temperatures yesterday were slightly cooler due to the northerly flow and a few clouds across the region. Overnight temperatures across most of the forecast area dropped just below freezing. Today southwesterly winds and sunny skies should return causing temperatures to climb to almost record highs. Remote sensors throughout the area already report temperatures in the upper 30's and low 40's. Starting tonight a low pressure system should move into the region. By tomorrow the forecast area should see much cooler temperatures, some clouds, north / east winds, and a slight chance of snow showers.

Last night's clear skies and below freezing temperatures allowed the snow surfaces that melted yesterday to refreeze. As the sun hits the slopes and the temperatures rise today these refrozen surfaces should soften quickly. Water produced today during the melting phase of the melt-freeze cycle will weaken the snowpack by dissolving bonds within and between layers. Higher daytime temperatures and more solar radiation should cause the melt water to penetrate deeper into the snowpack today. As the temperatures cool tonight and over the next few days the freezing phase of the melt-freeze cycle should become dominate making the snowpack stronger as the water turns to ice and cements the wet layers in place.

On southerly aspects the top 4 to 6 inches of snow has repeatedly melted and refrozen during this cycle. Below this surface layer observations show well bonded and strong snow. As melt water percolates deeper into the snowpack some of these stronger, lower layers could serve as boundaries where water concentrates and dissolves the bonds within and between layers forming a weak layer or sliding surface that could result in wet snow avalanches. On northerly aspects, observations from across the forecast area continue to show settlement, strong layer bonding, and a cold snowpack.

Today, northerly aspects that were sheltered from the winds will continue to hold cold and unconsolidated surface snow. On east through northwest aspects that were exposed to the winds last week, the snow surface is a mix of wind scoured crusts, hardpack, and other wind affected surfaces. Southerly aspects will have melt-freeze / corn conditions. As daytime warming occurs, human triggered wet snow avalanches will become possible on steep sun exposed SE-S-SW-W aspects. Gradual warming over the past week, February sun angles (the sun is still relatively low in the sky), and an overnight refreeze should help limit the wet snow instabilities making natural avalanche activity unlikely today.
The bottom line: This morning, avalanche danger is LOW for all elevations and aspects. Areas of MODERATE avalanche danger will develop at all elevations on SE-S-SW-W aspects, 35 degrees and steeper due to daytime warming.

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): 30 deg. F
Max. temperature at Sierra Crest past 24 hours: 43 to 45 deg. F.
Average wind direction at Sierra Crest past 24 hours: East
Average wind speed at Sierra Crest past 24 hours: 22 mph
Maximum wind gust at Sierra Crest past 24 hours: 52 mph
New snow fall at 8,200 feet past 24 hours: 0 inches
Total snow depth at 8,200 feet: 84 inches
Mountain Weather Forecast For Today:
Sunny and warm with temperatures approaching record highs.
Temperature forecast for 8,000 to 9,000 feet: around 47 deg. F
Ridgetop winds forecast for the Sierra Crest: North at 10 mph shifting to the southwest.
Snowfall expected in the next 24 hours: trace
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, sunny with daytime highs 50 to 56 deg. F. Winds out of the east at 10 mph shifting to the southwest.

Tonight, clear skies becoming partly cloudy with overnight lows 25 to 31 deg. F. Southwest winds at 10 to 20 mph.

For Wednesday, mostly cloudy skies with a chance of isolated snow showers. Daytime highs around 36 deg. F. West winds at 10 to 15 mph shifting to the south with gusts to 25 mph in the afternoon.

Above 8000 Feet:
Today, sunny with daytime highs around 47 deg. F. Winds out of the north at 10 mph shifting to the southwest.

Tonight, clear skies becoming partly cloudy with overnight lows 24 to 30 deg. F. Southwest winds at 10 to 15 mph with gusts to 30 mph shifting to the west and increasing to 15 to 25 mph with gusts to 40 mph after midnight.

For Wednesday, mostly cloudy skies with a chance of isolated snow showers. Daytime highs around 32 deg. F. Northwest winds at 15 to 25 mph with gusts to 50 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:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.