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 February 23, 2008:


February 23, 2008 at 1:00 am

Forecast Discussion:


This advisory was posted on February 23, 2008 7:00 AM
Click here for a detailed map of the SAC forecast area

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Today's Advisory:

This morning avalanche danger is MODERATE near and above treeline on wind loaded NW-N-NE-E aspects, 35 degrees and steeper. Below treeline, avalanche danger is LOW with isolated pockets of MODERATE danger on wind affected open slopes steeper than 38 degrees. The avalanche danger will increase late today and overnight as a winter storm impacts the area.

A large winter storm approaching the area should pull warm subtropical air into the area bringing snow levels up to 6500' this afternoon and evening. Overnight freezing levels should drop 5000'. The forecast calls for 1 to 3 feet of new snow above 7000'. Steady southerly winds between 30 and 50 mph with gusts exceeding 100 mph along the ridgetops should begin this evening and continue through Sunday.

In the last 24 hrs only 3 to 6 inches of new snow fell north of Highway 50 while areas south Highway 50 report 6 to 12 inches. Overnight the snowfall tapered off and some settlement occurred in the new snow. The new snow still has not bonded well to the old snow surfaces. Yesterday observers reported human triggered avalanches that failed at this interface on N-NE facing slopes steeper than 35 degrees near and above treeline in the Mount Judah area and in the Huckleberry Canyon area (near Echo Summit). A skier triggered one of the slides in the Mount Judah area remotely from the ridgeline (see photo and crown profile). Crown heights ranged from 14 inches to 2 feet with widths of 40 to 200 yards. No natural avalanche activity was reported.

The other concern today will be the timing of the winter storm and the initial high freezing levels associated with it. The exact snow level remains uncertain but should stay below 6500'. It could go as high as 7000'. If any precipitation falls as rain on new snow natural avalanche activity should occur. Since the forecast calls for the bulk of the storm to impact the area overnight the avalanche danger should not rise much today. Natural avalanche activity could become likely due to new snowfall and increased wind loading overnight. If the storm arrives earlier the avalanche danger will increase earlier.

Natural avalanche activity should be unlikely but not impossible today unless rain falls on new snow. Continued wind loading and the weak interface between the old snow surfaces and new snow should cause human triggerable avalanches that fail at the old/new snow interface to remain possible today in steep wind loaded areas near and above treeline. Below treeline today most avalanche activity is unlikely. However, some small isolated human triggerable slabs could still remain on steep, open, wind affected slopes.

The bottom line: This morning avalanche danger is MODERATE near and above treeline on wind loaded NW-N-NE-E aspects, 35 degrees and steeper. Below treeline, avalanche danger is LOW with isolated pockets of MODERATE danger on wind affected open slopes steeper than 38 degrees. The avalanche danger will increase late today and overnight as a winter storm impacts the area.

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): 14 deg. F
Max. temperature at Sierra Crest past 24 hours: 24 deg. F.
Average wind direction at Sierra Crest past 24 hours: Southwest
Average wind speed at Sierra Crest past 24 hours: 20 mph
Maximum wind gust at Sierra Crest past 24 hours: 47 mph
New snow fall at 8,200 feet past 24 hours: 3 to 6 inches north of Highway 50 and 6 to 12 inches south of Highway 50
Total snow depth at 8,200 feet: 92 inches
Mountain Weather Forecast For Today:
Partly cloudy this morning then increasing clouds and snow moving into the area by this afternoon.
Temperature forecast for 8,000 to 9,000 feet: around 27 deg. F
Ridgetop winds forecast for the Sierra Crest: South at 15 to 20 mph with gusts to 35 mph increasing to 20 to 30 mph with gusts to 55 mph this afternoon
Snowfall expected in the next 24 hours: 15 to 27 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, partly cloudy this morning then increasing clouds and snow moving into the area by this afternoon. Snow accumulation 1 to 3 inches. Daytime highs around 31 deg. F. South winds at 10 to 15 mph with gusts to 25 mph.

Tonight, snow with accumulation 12 to 22 inches. Overnight lows around 25 deg. F. South winds at 20 to 30 mph with gusts to 45 mph.

For Sunday, snow decreasing in the afternoon. Snow accumulation 6 to 10 inches. Daytime highs around 31 deg. F. Southwest winds at 20 to 30 mph with gusts to 55 mph.

Above 8000 Feet:
Today, partly cloudy this morning then increasing clouds and snow moving into the area by this afternoon. Snow accumulation 1 to 3 inches. Daytime highs around 27 deg. F. South winds at 15 to 20 mph with gusts to 35 mph increasing to 20 to 30 mph with gusts to 55 mph this afternoon.

Tonight, snow with accumulation 14 to 24 inches. Overnight lows 18 to 24 deg. F. South winds at 25 to 35 mph increasing to 30 to 45 mph with gusts to 85 mph after midnight.

For Sunday, snow decreasing in the afternoon. Snow accumulation 8 to 12 inches. Daytime highs 22 to 28 deg. F. Southwest winds at 30 to 45 mph with gusts to 85 mph increasing to 40 to 50 mph with gusts to 95 mph in the afternoon afternoon.


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.