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 11, 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, 37 degrees and steeper due to daytime warming.

Remote sensors indicate that air temperatures hovered around freezing across the forecast area last night. Today slightly cooler air temperatures and light north/east winds should occur as the low pressure system to the north moves east. The few high clouds associated with this disturbance should dissipate by mid morning. The high pressure ridge should strengthen during the day bringing even warmer temperatures back into the area tomorrow.

Radiational cooling and slightly colder the nighttime lows should have allowed the snow surfaces that melted yesterday to undergo a slightly more robust refreeze last night. During melt-freeze cycles the snowpack gets weaker during the melting phase as free water dissolves bonds within and between layers. During the freezing phase it gets stronger as the water turns to ice and cements the wet layers in place. Relativly warm overnight temperatures, continued sun, and warm daytime temperatures over the next few days should cause the freezing phase to get shorter and the melting phase to last longer allowing melting to occur deeper in the snowpack.

This melt-freeze process should primarily affect the southerly aspects where observations show the top 4 to 6 inches of snow has repeatedly become wet and weak due to daytime warming. 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 earlier this 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 and should soften quickly today. 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, and a cool north / east wind should help limit the wet snow instabilities. As a result, natural avalanche activity is 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, 37 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): 32 deg. F
Max. temperature at Sierra Crest past 24 hours: 40 to 49 deg. F.
Average wind direction at Sierra Crest past 24 hours: West shifting to the north and east
Average wind speed at Sierra Crest past 24 hours: 18 mph
Maximum wind gust at Sierra Crest past 24 hours: 41 mph
New snow fall at 8,200 feet past 24 hours: 0 inches
Total snow depth at 8,200 feet: 85 inches
Mountain Weather Forecast For Today:
Some high clouds this morning then clearing.
Temperature forecast for 8,000 to 9,000 feet: around 44 deg. F
Ridgetop winds forecast for the Sierra Crest: North at 10 to 15 mph.
Snowfall expected in the next 24 hours: 0 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, partly cloudy this morning and clearing quickly. Daytime highs around 47 deg. F. Winds out of the northeast at 10 mph.

Tonight, clear skies with overnight lows 22 to 30 deg. F. East winds at 10 to 15 mph.

For Tuesday, sunny skies with daytime highs 48 to 54 deg. F. East winds at 10 mph shifting to the southwest in the afternoon.

Above 8000 Feet:
Today, partly cloudy this morning and clearing quickly. Daytime highs around 44 deg. F. Winds out of the north at 10 to 15 mph.

Tonight, clear skies with overnight lows 24 to 32 deg. F. East winds at 10 to 15 mph.

For Tuesday, sunny skies with daytime highs around 45 deg. F. North winds at 10 mph shifting to the southwest in the afternoon.

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