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 December 24, 2007 7:00 AM
Click here for a detailed map of the SAC forecast area

low avalanche danger
Today's Advisory:
The avalanche danger is LOW at all elevations and aspects. Avalanche activity is unlikely today but not impossible. Some small, isolated pockets of instability may still exist in the Mount Rose area near and above treeline on N-NE-E aspects, 35 degrees and steeper.

A strong cold front moving southeast from the Pacific Northwest should move into western NV today. It should drag a cold, dry airmass into the forecast area causing temperatures to drop signifigantly over the next 24 hours. The winds should also increase as this system passes through. The ridgetop winds have already started gusting into the 70's. These winds should shift directions from the SW to the ENE and diminsih over the next 24 hours.

Mild temperatures, calm winds, and settlement continue to help the snowpack gain strength. In many areas along the crest the snow grains continue to round and form stronger bonds between each other and between the layers in the snowpack. Failure of any of the layer interfaces during layer bonding tests requires more force with each passing day. This trend is more gradual in the Mount Rose area where a more developed layer of facets (weak, sugary snow grains) exists. Forming strong bonds between these facets and the layers above them will be a slower process. The layers above the facets are a mix of dense snow grains, crusts, and new snow. These upper layers are gaining strength much faster than the facets in the lower part of the snowpack. As these upper layers become stronger it should take a larger trigger to transmit enough energy through the snowpack to cause a failure in the facets. In areas where a thinner snowpack exists it may be possible to trigger a failure in the faceted layer today. Mostly these areas also have enough anchors to keep fractures from propogating very far. Even though avalanche activity is unlikely today there may be a few small areas where a trigger point (shallowly buried rocks, logs, cliff bands, and other areas where the snowpack is thinner) connects the shallow snowpack to an area where the snowpack is deeper. Failures iniated at such a trigger point could propogate out into the deeper area. Avalanches resulting from this combination should be small, isolated, and rare today.

As the wind increases and shifts direction again today stiff wind slabs will continue to form. Test slopes and layer bonding test indicate that these slabs have bonded to the layers below them. Avalanche activity involving these slabs is unlikely today but not impossible.

The bottom line: The avalanche danger is LOW at all elevations and aspects. Avalanche activity is unlikely today but not impossible. Some small, isolated pockets of instability may still exist in the Mount Rose area near and above treeline on N-NE-E aspects, 35 degrees and steeper.

The next update to the advisory will occur on December 26, 2007 at 7:00am.

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: 38 deg. F
Average wind direction at Sierra Crest past 24 hours: East shifting to the southwest
Average wind speed at Sierra Crest past 24 hours: 25 mph
Maximum wind gust at Sierra Crest past 24 hours: 86 mph
New snow fall at 8,200 feet past 24 hours: 0 inches
Total snow depth at 8,200 feet: 31 inches
Mountain Weather Forecast For Today:
Partly cloudy skies.
Temperature forecast for 8,000 to 9,000 feet: 35 to 40 deg. F in th morning dropping to 25 to 30 deg. F. this afternoon.
Ridgetop winds forecast for the Sierra Crest: Southwest at 45 to 55 mph with gusts to 80mph shifting to the northwest at 20 to 35 mph with gusts to 65 mph.
Snowfall expected in the next 24 hours: 0 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, partly cloudy skies with daytime highs 35 to 40 deg. F. in the morning. Temperatures should drop to 30 to 35 deg. F by the afternoon. West winds at 15 to 25 mph with gusts to 35 mph in the morning shifting to the northwest by the afternoon.

Tonight, partly cloudy skies with with overnight lows 16 to 22 deg. F. East winds at 10 to 15 mph.

For Tuesday, mostly cloudy skies with daytime highs 31 to 36 deg. F. East winds at 10 to 15 mph

Above 8000 Feet:
Today, partly cloudy skies with daytime highs 35 to 40 deg. F. in the morning. Temperatures should drop to 25 to 30 deg. F by the afternoon. Southwest winds at 45 to 55 mph with gusts to 80 mph in the morning shifting to the northwest by the afternoon.

Tonight, partly cloudy skies with with overnight lows 18 to 23 deg. F. Northeast winds at 30 to 45 mph with gusts to 70 mph.

For Tuesday, mostly cloudy skies with daytime highs 27 to 31 deg. F. Northeast winds at 10 to 15 mph with gusts to 35 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:
	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.