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 15, 2007:


February 15, 2007 at 1:00 am

Forecast Discussion:


This advisory was posted on Thursday, February 15th, 2007 at 7:01 am

The bottom line: Along the Sierra Crest near and above treeline, the avalanche danger is LOW. Below treeline, avalanche danger is LOW. Low danger does not mean no danger. There still may be some small isolated instabilities on wind loaded slopes. In the Mt. Rose area the avalanche danger is LOW with small pockets of MODERATE avalanche danger on N-NE aspects 35 degrees and steeper. Small human triggered avalanches remain possible today on those slopes. Natural avalanches are unlikely. Normal caution is advised for traveling in the backcountry.

As a storm system continues to move through the Pacific Northwest, we should see more cloud cover and warmer temperatures in our forecast area. The winds have started shifting to the northeast along the Sierra crest and should continue from that direction for the next couple of days. After a brief lull last night, these winds picked back up and are expected to remain in the 25-30 mph range through Friday.

The east winds should continue scouring snow from the upper portion of N-NE-E aspect avalanche start zones today further reducing the potential for surface snowpack instability on those aspects. These winds should result in light to moderate loading on the W-SW-S aspects. It is unlikely that this will add enough additional load to cause avalanche activity on these slopes. Throughout most of the forecast area the snowpack is gaining strength. Layer bonding tests indicate that the weaknesses created in the most recent snow during the storm are rapidly consolidating. These tests and other observations also indicate that the bond between the old snow surfaces and the storm snow is gaining strength as are the layer interfaces deeper in the snowpack. The exception to this trend is in the Mt. Rose area on the northerly aspects that had a shallow snowpack prior to the storm. These are the slopes where a layer of weak, sugary, cup shaped snowgrains known as depth hoar formed earlier in the season. This depth hoar does not form bonds very easily, and it is still very weak. In most places the more dense, well bonded, upper layers of the snowpack are preventing force from reaching this weak layer. However, a trigger in just the right spot could cause it to fail. The right spot would be places where the weak layer is weaker or closer to the surface like near rocks or trees or where the snowpack is shallow. Another way that force could get to this weak layer is by putting a larger trigger such as more than one person or snowmobile on these slopes. Remember that even though the avalanche danger has decreased it is always a good idea to use safe travel techniques when traveling in the backcountry.

No avalanches were reported yesterday.

The bottom line: Along the Sierra Crest near and above treeline, the avalanche danger is LOW. Below treeline, avalanche danger is LOW. Low danger does not mean no danger. There still may be some small isolated instabilities on wind loaded slopes. In the Mt. Rose area the avalanche danger is LOW with small pockets of MODERATE avalanche danger on N-NE aspects 35 degrees and steeper. Small human triggered avalanches remain possible today on those slopes. Natural avalanches are unlikely. Normal caution is advised for traveling in the backcountry.

At this time, we have not raised enough money to meet our operating budget for this year. If you use this service with any regularity and would like to continue to do so, please show your support for the Sierra Avalanche Center. You may make a tax deductible donation directly to us via Paypal or by sending a check to our address listed above, c/o the Truckee Ranger Station. A financial graph showing the current fundraising and budget numbers is available by clicking here. The financial support already received this winter from a variety of users is greatly appreciated.

Andy Anderson , Avalanche Forecaster
Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet):
28 deg. F
Max. temperature at Sierra Crest past 24 hours:
29 deg. F
Average wind direction at Sierra Crest past 24 hours:
northeast
Average wind speed at Sierra Crest past 24 hours:
20 mph
Maximum wind gust at Sierra Crest past 24 hours:
44 mph
New snow fall at 8,200 feet past 24 hours:
0 inches
Total snow depth at 8,200 feet:
56 inches
Mountain Weather Forecast For Today:
Mostly cloudy.
Temperature forecast for 8,000 to 9,000 feet:
40 - 45 deg. F
Ridgetop winds forecast for the Sierra Crest:
Northeast 20 - 30 mph, gusting to 50 mph
Snowfall expected in the next 24 hours:
0 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet
Today, mostly cloudy skies with daytime highs 43 to 48 degrees F. North winds at 5 to 15 mph. Tonight, partly cloudy with lows 25 to 30 degrees F. North winds at 10 to 20 mph. Friday, partly cloudy skies with daytime highs 44 to 49 degrees F. North winds at 10 to 20 mph are expected.

Above 8000 Feet
Today, mostly cloudy skies with daytime highs 40 to 45 degrees F. Northeast winds at 20 to 30 mph, gusting to 50 mph. Tonight, partly cloudy with lows 30 to 35 degrees F. Northeast winds at 20 to 30 mph with gusts to 50 mph. Friday, partly cloudy skies with daytime highs 41 to 46 degrees F. Northeast winds at 15 to 25 mph gusting to 50 mph are expected.


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.