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 Avalanche Advisory was published on January 6, 2007:


January 6, 2007 at 1:00 am

Forecast Discussion:


This advisory was posted on Saturday, January 5, 2007 at 7:00 am

After blowing from the east for most of the day yesterday, the winds are predicted to shift back to the north today due to a small disturbance passing to the north of the forecast area. This small disturbance will also bring some high clouds and warmer weather to the region today. A strong high pressure should settle over us for the next few days bringing warm temperatures and moderate north winds.

Even though the initial storm snow bonded quite well to the old snow surface, the cold temperatures that remained following the storm continue to prevent the colder, less dense snow that fell throughout the rest of the storm from consolidating or building very strong bonds with the snow below it. On the north aspects the surface of this new snow is starting to facet creating a thin weak layer. This snow is also still available for wind transport. So far the winds have moved this snow in 2 major directions: first during the storm the SW winds loaded NE slopes, then after the storm the winds shifted to the E and ENE and moved snow from the NE slopes to the NW slopes. Today they will shift to the north and be able to move this same snow a third time. This time both the NE and NW slopes will be cross loaded creating complex windslabs from three different wind directions on these slopes. As the winds continue to move this same snow, the snow gets packed closer together and the windslabs it forms will become denser and stiffer. The combination of scouring, loading, and some near surface faceting that the snow on these slopes has undergone over the last few days will leave us with a varied snow surface that will form great bonds with today's windslabs in some places and poor bonds with them in other places. Even though it will be hard to transmit force through the hard slabs down to the layers below them, this variation in bonding will allow small areas where a human triggered avalanche is possible on the NW and NE slopes today. Since the slabs are likely to be hard, dense and stiff, they are more likely to propagate fractures if there is enough force to initiate a failure in them. In most places this will not be too much of an issue since many of these hard slabs will be patchy and disconnected, but watch out for places where these hard slabs extend over large areas. These hard slabs would be easiest to trigger from areas where the slab is thin like near rocks, trees, the edges of the slab, and near cliffs. There are also a few isolated pockets of windslabs left over on the N-NE-E slopes. These are mostly at upper elevations and on small terrain features that are protected from the east winds.

Above treeline the avalanche danger is MODERATE. Avalanche activity is most likely on recently wind loaded NW-N-NE-E aspects, 35 degrees and steeper. Below treeline the avalanche danger is LOW.

Andy Anderson , Avalanche Forecaster

Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet):
21 deg. F
Max. temperature at Sierra Crest past 24 hours:
22 deg. F
Average wind direction at Sierra Crest past 24 hours:
East shifting to the north
Average wind speed at Sierra Crest past 24 hours:
35-45 mph
Maximum wind gust at Sierra Crest past 24 hours:
78 mph
New snow fall at 8,200 feet past 24 hours:
0 inches
Total snow depth at 8,200 feet:
42 inches
Mountain Weather Forecast For Today:
Mostly sunny with a few scattered high clouds
Temperature forecast for 8,000 to 9,000 feet:
27-37 degrees F.
Ridgetop winds forecast for the Sierra Crest:
North 30 - 40 mph, G 55 mph
Snowfall expected in the next 24 hours:
0 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet
For today, mostly sunny with a few scattered high clouds. Highs 27 to 37 degrees F. North winds 10 to 20 mph. Overnight clear with lows 15-25 degrees F. North winds at 10 to 20 mph. Sunday will be sunny and warmer. Daytime highs 33-43 degrees F. North winds at 10-20 mph.

Above 8000 Feet
For today, mostly sunny with a few scattered high clouds. Highs 27 to 37 degrees F. North winds 30 to 40 mph with gusts to 55 mph. Overnight clear with lows 23-33 degrees F. North winds at 30 to 40 mph with gust increasing from 55 mph to 70 mph after midnight. Sunday will be sunny and warmer. Daytime highs 30-40 degrees F. North winds at 30-40 mph with gusts to 70 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:

  Saturday: Saturday Night: Sunday:
Weather:
Temperatures: deg. F. deg. F. deg. F.
Wind direction:
Wind speed:
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Saturday: Saturday Night: Sunday:
Weather:
Temperatures: deg. F. deg. F. deg. F.
Wind direction:
Wind speed:
Expected snowfall: O in. O in. O in.