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 advisory was posted on Tuesday, March 13th, 2007 at 7:00 am

The bottom line: Avalanche danger is MODERATE on sun exposed E-SE-S-SW aspects with slopes steeper than 35 degrees at all elevations. Human triggered wet snow avalanches are possible today due to daytime warming. Even though natural wet snow avalanches are unlikely, they are not impossible. Today is a good day to avoid those southerly slopes once they warm up. Use good snow assessment and safe travel techniques to minimize risks.

Temperatures are forecasted to be slightly cooler today as a weak disturbance approaches the area. This small front should bring some cloud cover and cooler temperatures to the region overnight and through tomorrow. Ridgetop winds have increased and shifted to the southwest ahead of this system. The high pressure ridge should rebuild after this system passes through. Clear skies and warmer temperatures are forecasted to return for the rest of the week.

Last night the overnight lows were above freezing again. The overnight lows along the Sierra Crest last night were around 41 degrees F. In the Mt. Rose area the overnight low was around 40 degrees F. That is the third night in a row that temperatures never dropped below freezing in the mountains. Radiational cooling of the snowpack is allowing the snow surface to refreeze in most places. With more above normal temperatures and sunny skies forecasted for today, the snow should soften very fast becoming wet and sloppy after a short time in the sun.

This warm springtime weather marks the first significant extended period of intense solar radiation and prolonged high air temperatures for the forecast area. As snowpack goes through more cycles of melting and freezing, the temperatures throughout the snowpack are becoming more uniform (isothermal) and the layers in the snowpack are becoming more homogeneous. There are still a few colder, more fine-grained, winter layers and crusts buried in the snowpack. As the snow melts and water percolates down dissolving bonds between the snow grains, the water could easily collect in these locations. Water at these crust interfaces and colder, more fine-grained snow layers could weaken the bonds in these areas and allow them to serve as weak layers whose failure could cause wet snow avalanches. As the temperatures cool slightly today and tomorrow this process should become more gradual allowing the snowpack to more easily adjust to the changes. Over time melt-water pathways will form in the snowpack, and these areas of weakness will become less of an issue.

One good indicator of wet snow instability is surface instabilities like rollerballs and pinwheels. Another good indicator that the slope has warmed up to the point that wet avalanches may occur is when boot penetration exceeds ankle height. An easy way to check this is to step off of your equipment. If you sink into wet snow to the top of your boots, it is time to move to a less sun exposed aspect or call it a day.

Roller balls and large human triggered pinwheels have been reported on the most aspects over the last few days. No human triggered or natural wet snow avalanches have been reported, despite these signs of surface instability. As air temperatures continue to warm today, the possibility of wet snow avalanche activity will increase.

The bottom line: Avalanche danger is MODERATE on sun exposed E-SE-S-SW aspects with slopes steeper than 35 degrees at all elevations. Human triggered wet snow avalanches are possible today due to daytime warming. Even though natural wet snow avalanches are unlikely, they are not impossible. Today is a good day to avoid those southerly slopes once they warm up. Use good snow assessment and safe travel techniques to minimize risks.

At this time, we are still short $3,000 in funding for our operating budget this winter. If you use this service with any regularity and would like to continue to do so, please show your financial 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 graph showing the amount of fundraising completed this season and our overall budget 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):
41 deg. F
Max. temperature at Sierra Crest past 24 hours:
55-58 deg. F
Average wind direction at Sierra Crest past 24 hours:
Southwesterly
Average wind speed at Sierra Crest past 24 hours:
15-20 mph
Maximum wind gust at Sierra Crest past 24 hours:
30 mph
New snow fall at 8,200 feet past 24 hours:
0 inches
Total snow depth at 8,200 feet:
81 inches
Mountain Weather Forecast For Today:
Sunny skies
Temperature forecast for 8,000 to 9,000 feet:
51 to 57degrees F.
Ridgetop winds forecast for the Sierra Crest:
West Southwest 20-30 mph with gusts to 50 mph
Snowfall expected in the next 24 hours:
0 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet

Today, sunny with daytime highs 57 to 63 degrees F. West winds at 10 to 20 mph with gusts to 30 mph. Tonight, partly cloudy skies with overnight lows 32 to 38 degrees F. Southwest winds at 10 to 15 mph with gusts to 30 mph. Wednesday, partly cloudy skies with daytime highs 53 to 59 degrees F. West winds at 10 to 20 mph with gusts to 30 mph are expected.

Above 8000 Feet

Today, sunny with daytime highs 51 to 57 degrees F. Southwest winds at 20 to 30 mph with gusts to 50 mph. Tonight, partly cloudy skies with overnight lows around 36 degrees F. Southwest winds at 20 to 30 mph with gusts to 60 mph. Wednesday, partly cloudy skies with daytime highs 47 to 53 degrees F. West winds at 15 to 25 mph with gusts 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:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.