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 Sunday, March 18th, 2007 at 7:00 am

The bottom line: This morning, avalanche danger is LOW for all aspects and elevations. As daytime warming occurs, avalanche danger will increase to MODERATE on sun exposed E-SE-S-SW aspects 35 degrees and steeper at all elevations.

A small, weak low pressure system should bring cooler temperatures to the forecast area today. Temperatures should still be well above normal, and there is not much cloud cover associated with this small system. This low is the precursor to a larger low pressure system that should bring more normal temperatures and some precipitation to the area starting later in the day on Monday. The winds should remain light from the southwest through today. They should start to gain intensity during the day on Monday as the low pressure system approaches.

Overnight low temperatures still stayed above freezing in the mountains even though they were around 5 degrees F cooler than they have been for the past few nights. Another clear night and these cooler temperatures should allow a more robust refreeze to occur in the upper several inches of snow due to radiational cooling. Wet, unfrozen snow still persists from day to day underneath the refrozen crust layer. Since the air temperatures are forecasted to be slightly cooler, it should take slightly longer for this refrozen surface snow to soften today. In most sun exposed areas the snow has undergone enough melt-freeze cycles for good corn conditions to form on the surface especially on the SW-S-SE-E aspects. The best time to harvest this corn is just as the refrozen bonds between the grains start to melt in the mid morning hours. By midday the heat of the day turns the corn into wet, punchy, slush that is not much fun to ride and is more dangerous and less stable.

The daily melt-freeze cycles and isothermal conditions in the upper snowpack continue to promote uniformity in the snowpack. In the long run this trend will help to strengthen the snowpack. However, everyday during the afternoon when the melting part of this process is at its height, water will be percolating through the snowpack causing bonds to dissolve between the snow grains. Areas where this water can percolate to a smooth surface like a slab of rock and then flow along that surface lubricating it, could potentially become failure surfaces for wet slab avalanches. This process should be more exaggerated around the few glide cracks that have formed in the forecast area. There are also still a few areas at higher elevations where some less dense layers of snow exist in the upper 1-2 ft of the snowpack. These less dense layers could serve as weak layers for wet snow avalanche activity as the the day warms up, and they become saturated with water. Human triggered whumphing has been observed after midday on S-SW slopes around 8500' in the Mt. Rose area over the last two days on these layers. Warming instability that does occur today is expected to be limited to human triggering of wet surface snow.

Pay attention to signs of surface instability like pinwheels and rollerballs. Step off of your equipment and check boot penetration as daytime warming occurs. Avoid steep slopes where boot penetration exceeds boot top height. Human triggered wet snow avalanche activity will become possible today as daytime warming occurs. Natural wet snow avalanche activity is unlikely, but not impossible.

The bottom line: This morning, avalanche danger is LOW for all aspects and elevations. As daytime warming occurs, avalanche danger will increase to MODERATE on sun exposed E-SE-S-SW aspects 35 degrees and steeper at all elevations.

Our next fundraiser will occur on March 25th at Sugar Bowl Ski Area. For more information, click here or visit our homepage by clicking on the toolbar up top. At this time, we are still short $2,000 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):
39 deg. F
Max. temperature at Sierra Crest past 24 hours:
56 deg. F
Average wind direction at Sierra Crest past 24 hours:
Southwesterly
Average wind speed at Sierra Crest past 24 hours:
20 mph
Maximum wind gust at Sierra Crest past 24 hours:
40 mph
New snow fall at 8,200 feet past 24 hours:
0 inches
Total snow depth at 8,200 feet:
70 inches
Mountain Weather Forecast For Today:
Sunny skies
Temperature forecast for 8,000 to 9,000 feet:
46 to 56 degrees F.
Ridgetop winds forecast for the Sierra Crest:
Southwesterly 15-30 mph.
Snowfall expected in the next 24 hours:
0 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, sunny skies with daytime highs 55 to 60 degrees F. Southwest winds at 5 to 15 mph. Tonight, partly cloudy skies with overnight lows 35 to 45 degrees F. Southwest winds at 5 to 15 mph. Monday, partly cloudy skies with some rain and snow showers becoming possible in the afternoon and evening. Daytime highs 49 to 54 degrees F. Southwest winds at 15 to 25 mph are expected.

Above 8000 Feet:
Today, sunny skies with daytime highs 46 to 56 degrees F. Southwest winds at 15 to 30 mph. Tonight, partly cloudy skies with overnight lows 35 to 45 degrees F. Southwest winds at 15 to 25 mph. Monday, partly cloudy skies with some snow showers becoming possible in the afternoon and evening. Daytime highs 40 to 50 degrees F. Southwest winds at 25 to 35 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:
	Sunday:	Sunday Night:	Monday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.