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 11, 2007:


January 11, 2007 at 1:00 am

Forecast Discussion:


This advisory was posted on Thursday, January 11, 2007 at 7:00 am

Yesterday the southwest winds gained strength, and they started to transport snow. They will continue out of the southwest today until they start shifting to the northeast as the storm moves out of the forecast area tonight. Only a trace of new snow fell on the mountains last night. Minor additional snowfall is expected today with only 1 to 2" of accumulation by this evening and another 1-3" overnight. By Friday most of the storm will have passed us leaving very cold, dry weather in its wake. In many places across the forecast area temperatures won't climb much above zero. Over the weekend it should start to warm back up some.

As the winds increased at the upper elevations on Tuesday and Wednesday, they started moving snow onto the N-NE-E aspects. There was not much snow available for transport so very few windslabs were able to form. However, today as we get a little new snow, the winds will have more snow to load onto those N-NE-E slopes. With only 2" of cold, low density snow forecasted by the end of the day, the windslabs that form today will be small and will not add much additional load to the current snowpack making natural avalanches unlikely. Above treeline these windslabs will be sitting on a mix of wind scoured surfaces, glazed crusts, and some left over hard slabs. This variation in existing surface conditions will create variations in how well these new windslabs bond to the existing snowpack. On some of the steeper more windloaded slopes, small sections of these new windslabs could be tender enough to be triggered by human activity on the slope by this afternoon. Even though these slides would likely be small, they could still push you into places you don't want to go. Watch out for terrain traps like cliffs, gullies, and creeks that will amplify the consequences of any size avalanche. At the lower elevations between 6000' and 7000' on northerly aspects, pockets of surface hoar will be buried by this new snow. The 2" of new snow should not be enough snow to make these buried surface hoar layers fail, but it will be enough to hide this layer and give it a little protection from the elements. This could pose a problem in the future because there will be a persistent weak layer in areas that most of us take for granted as the "approach" to the terrain above.

Today near and above treeline the avalanche danger is LOW for all non wind affected areas. On the N-NE-E aspects steeper than 35 degrees where windloading occurs today the avalanche danger will rise to MODERATE by this afternoon.

Below treeline today the avalanche danger remains LOW.

Andy Anderson , Avalanche Forecaster

Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet):
14 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:
50 mph
Maximum wind gust at Sierra Crest past 24 hours:
103 mph
New snow fall at 8,200 feet past 24 hours:
trace
Total snow depth at 8,200 feet:
40 inches
Mountain Weather Forecast For Today:
Intermittent snow showers with accumulations up to 2".
Temperature forecast for 8,000 to 9,000 feet:
10-15 deg. F dropping to 0 this afternoon. Wind chill 20-30 below zero.
Ridgetop winds forecast for the Sierra Crest:
Southwest winds 40 to 60 mph gusting to 75 mph
Snowfall expected in the next 24 hours:
2-3 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet
Today, intermittent snow showers with accumulations up to 2". Daytime highs 10-20 deg. F dropping into the single digits this afternoon. Wind chill 10 below zero. West winds 10 to 20 mph gusting to 40 mph. Overnight, snow showers with 1-3" of accumulation. Lows 5 below zero to 5 above zero. Wind chill 30 below zero. Northeast winds at 10 to 20 mph. Tomorrow will be mostly cloudy with a slight chance of snow showers. Daytime highs 0 to 10 degrees F. Wind chill 20 to 30 below zero. Northeast winds at 20 to 30 mph.

Above 8000 Feet
Today, intermittent snow showers with accumulations up to 2". Daytime highs 10-15 deg. F dropping to zero this afternoon. Wind chill 20-30 below zero. Southwest winds 40 to 60 mph gusting to 75 mph. Overnight, snow showers with 1-3" of accumulation. Lows 2 below zero to 12 below zero. Wind chill 30 to 40 degrees below zero. Northeast winds at 25 to 35 mph. Tomorrow will be mostly cloudy with a slight chance of snow showers. Daytime highs 5 below zero to 5 above zero. Wind chill 30 to 40 below zero. Northeast winds at 30 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:

  Thursday: Thursday Night: Friday:
Weather:
Temperatures: deg. F. deg. F. deg. F.
Wind direction:
Wind speed:
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Thursday: Thursday Night: Friday:
Weather:
Temperatures: deg. F. deg. F. deg. F.
Wind direction:
Wind speed:
Expected snowfall: O in. O in. O in.