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 December 23, 2006:


December 23, 2006 at 1:00 am

Forecast Discussion:


This advisory was posted on Saturday, December 23, 2006 at 6:44 am

Ridgetop winds remained easterly during the day yesterday and did not shift to westerly until around midnight last night. Air temperatures at the upper elevations are warmer this morning due to the return to westerly flow aloft. A weak weather system is approaching the forecast area and will bring light rain and snow later today. The next major storm system is expected to arrive Sunday night.

Yesterday morning, reports of purposeful skier triggered avalanches were widespread in the northern half of the forecast area. Snowpack failure occurred near the bottom of the storm snow on N-NE-E aspects. By mid morning, the east wind had scoured out snow from the avalanche start zones on N-NE-E aspects and caused significant wind loading and rapidly increasing instability on NW aspects in near and above treeline areas. In wind protected areas, stability tests continued to yield moderate force shears near the base of the storm snow on a variety of aspects yesterday. These shears occurred on needle and plate snow crystals which usually contribute to short term instability. A total of 3 inches of settlement has occurred within the storm snow thus far. The storm snow will continue to strengthen today in wind protected areas. Ridgetop winds shifted back around to westerly overnight and will begin to move snow back onto N-NE-E aspects today, prior to the onset of snowfall. Near surface snowpack instability is expected again today on heavily wind loaded NW-N-NE-E aspects in near and above treeline areas. Up to 3 inches of additional snow is possible overnight which will further contribute to wind loading and subsequent instability. Avalanche activity today is expected to occur on wind loaded slopes in response to human triggers.

Near and above treeline, avalanche danger is MODERATE on wind loaded NW-N-NE-E aspects 35 degrees and steeper. Below treeline, avalanche danger is LOW.

Brandon Schwartz, Avalanche Forecaster

Today's Central Sierra Weather Observations:

0600 temperature at Sierra Crest (8,700 feet):
26 deg. F
Max. temperature at Sierra Crest past 24 hours:
27 deg. F
Average wind direction at Sierra Crest past 24 hours:
easterly backing to westerly
Average wind speed at Sierra Crest past 24 hours:
30 mph
Maximum wind gust at Sierra Crest past 24 hours:
57 mph
New snow fall at 8,200 feet past 24 hours:
0 inches
Total snow depth at 8,200 feet:
34 inches

Mountain Weather Forecast For Today:

Mostly cloudy to cloudy skies with light rain and snow in the afternoon
Temperature forecast for 8,000 to 9,000 feet:
36 - 42 deg. F
Ridgetop winds forecast for the Sierra Crest:
westerly 25 - 40 mph, G 60 mph
Snowfall expected in the next 24 hours:
2 - 4 inches

2 Day Mountain Weather Forecast:

7000 to 8000 Feet
For today, mostly cloudy skies with a chance of snow in the afternoon. Snow accumulation up to 1 inch. Daytime highs 37 to 42 degrees F. Overnight lows 18 to 28 degrees F with snow likely. Snow accumulation up to 3 inches. Sunday will be mostly cloudy with a slight chance of snow showers. Daytime highs around 42 degrees F.

Above 8000 Feet
For today, mostly cloudy to cloudy skies with a chance of snow in the afternoon. Snow accumulation up to 1 inch. Daytime highs 36 to 42 degrees F. Winds out of the west at 25 to 40 mph with gusts to 60 mph. Overnight lows 19 to 25 degrees F with snow likely. Westerly winds 25 to 35 mph with gusts to 60 mph decreasing after midnight. Sunday will be mostly cloudy with a slight chance of snow showers. Daytime highs around 39 degrees F. Southwesterly ridgetop winds 10 to 15 mph with gusts to 25 mph are expected on Sunday.


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.