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 4, 2008 6:57 AM
Click here for a detailed map of the SAC forecast area

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Today's Advisory:

This morning, avalanche danger is CONSIDERABLE at all elevations. As the day progresses, avalanche danger is expected to rise to EXTREME danger near and above treeline on NW-N-NE-E-SE aspects, 32 degrees and steeper. Below treeline, avalanche danger will rise to CONSIDERABLE with pockets of HIGH danger in open areas 35 degrees and steeper.

A weak weather system passed through the forecast area overnight, depositing 4 to 6 inches of new snow along the Sierra Crest and around 3 inches of new snow in the Mount Rose area. Ridgetop winds began increasing yesterday morning, exceeding forecasted expectations by gusting over 100 mph from mid morning on. Southwest winds have decreased somewhat this morning, but are expected to gust over 150 mph as a very powerful storm system impacts the forecast area today. Warmer air has moved into the forecast area early this morning ahead of the approaching storm. Snow levels are on the rise this morning and are expected to climb to 7,000'-7,500', before rapidly falling to 4,000' or lower beginning around noon today. Snow accumulation above 8,000' in the next 24 hours is forecasted at 3 to 5 feet with locally higher amounts along the Sierra Crest of 6 feet in the northern portion of the forecast area and up to 7 feet in the southern portion of the forecast area.

Two major concerns exist for snowpack instability today. The first is warming air temperatures and the second is expected snowfall rates exceeding 6 inches per hour. As snow levels rise, a rain on new snow event is expected to occur as high as 7,500' where 4 to 6 inches of new snow will rapidly become unstable in steep areas on all aspects, both above and below treeline. Pay specific attention to terrain trap areas such as creek beds and road cuts. Warming air temperatures will also deposit higher density snow on top of lower density new snow in areas above 7,500'. This will increase the potential for slab formation and create a likely failure layer as new snow is rapidly loaded on top of this layer as the day progresses.

Sustained snowfall rates of at least 6 inches per hour are expected for a 6 hour time period during the day today. Within that time period, snowfall rates could reach as high as 8 to 9 inches per hour for a short time. This combined with additional deposition from wind loading and cross loading will add new snow to slopes faster that the snow can adjust and remain stable. The majority of widespread avalanche activity is expected to occur within the new snow or near the old/new snow interface where a layer melt-freeze crust, wind crust, or near surface faceted snow crystals exists, depending on location. Snowpack failure into the basal faceted layer at ground level is a possibility, especially once a large avalanche is already in motion.

Below 7,500', natural avalanches are possible and human trigger avalanches are probable on all steep aspects where rain falls on 4 to 6 inches of new snow this morning. As the main force of the storm hits today, very rapid snow accumulation is expected to make widespread natural and human triggered avalanches certain near and above treeline on steep NW-N-NE-E-SE aspects. Below treeline, natural avalanches are expected to become possible to likely and human triggered avalanche are expected to become probable to likely in steep open areas on all aspects.

The bottom line: This morning, avalanche danger is CONSIDERABLE at all elevations. As the day progresses, avalanche danger is expected to rise to EXTREME danger near and above treeline on NW-N-NE-E-SE aspects, 32 degrees and steeper. Below treeline, avalanche danger will rise to CONSIDERABLE with pockets of HIGH danger in open areas 35 degrees and steeper.

Please send us your snow, weather, and avalanche observations by clicking the submit observations link on our contact page.

Brandon Schwartz, Avalanche Forecaster

Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet): 27 deg. F
Max. temperature at Sierra Crest past 24 hours: 28 deg. F
Average wind direction at Sierra Crest past 24 hours: Southwest
Average wind speed at Sierra Crest past 24 hours: 60 mph
Maximum wind gust at Sierra Crest past 24 hours: 120 mph
New snow fall at 8,200 feet past 24 hours: 4 to 6 inches
Total snow depth at 8,200 feet: 34 inches

Mountain Weather Forecast For Today:
Heavy snowfall and very strong winds.
Temperature forecast for 8,000 to 9,000 feet: 25 to 30 deg. F
Ridgetop winds forecast for the Sierra Crest: Southwest at 80 to 100 mph with gusts to 150 mph.
Snowfall expected in the next 24 hours: 40 to 80 inches possible

2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, cloudy skies with heavy snowfall. Snow accumulation 15 to 30 inches. Daytime highs 30 to 35 deg. F. Southwest winds at 30 to 50 mph, with gusts to 100 mph.

Tonight, cloudy skies with heavy snowfall. Snow accumulation 15 to 30 inches. Overnight lows around 21 deg. F. Southwest winds at 20 to 35 mph with gusts to 70 mph, decreasing to gusts to 60 mph after midnight.

For Saturday, cloudy skies with snow showers. Snow accumulation 2 to 5 inches. Daytime highs around 25 deg. F. Southwest winds at 20 to 35 mph with gusts to 50 mph, increasing to 60 mph in the afternoon.

Above 8000 Feet:
Today, cloudy skies with heavy snowfall. Snow accumulation 18 to 36 inches with locally higher amounts. Daytime highs 25 to 30 deg. F. Southwest winds at 70 to 95 mph, with gusts to 150 mph, decreasing to 65 to 80 mph in the afternoon.

Tonight, cloudy skies with heavy snowfall. Snow accumulation 16 to 30 inches. Overnight lows 16 to 22 deg. F. Southwest winds at 45 to 65 mph with gusts to 150 mph, decreasing to 35 to 55 mph with gusts to 100 mph after midnight.

For Saturday, cloudy skies with snow showers. Snow accumulation 2 to 5 inches. Daytime highs around 22 deg. F. Southwest winds at 35 to 55 mph with gusts to 85 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:
	Friday:	Friday Night:	Saturday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Friday:	Friday Night:	Saturday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.