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 March 18, 2008:


March 18, 2008 at 0:00 am

Forecast Discussion:


This advisory was posted on March 18, 2008 7:00 AM

A map of the SAC forecast area is available on our home page.

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Today's Advisory:
The avalanche danger is MODERATE at all elevations on all sun exposed aspects, 37 degrees and steeper that have significant storm snow on them. Isolated pockets of CONSIDERABLE danger could develop on the most heavily wind loaded, sun exposed slopes at all elevations. Steep cross loaded NW and SE facing gullies and wind loaded SW-W slopes will be the most suspect.

A high pressure ridge over the forecast area should cause temperatures to be 8 to 10 degrees warmer today than they were yesterday. The winds should start to shift to the west and southwest as a series of low pressure systems brushes the northern end of the forecast area. These systems could bring some isolated snow showers to the Sierra tomorrow afternoon and should cause temperatures to cool down to a more normal range tomorrow. The forecast also calls for a gradual increase in cloud cover over the next 36 hours.

Observations from the Tremor Peak (near Heavenly) and Mt. Rose areas yesterday indicate that the new snow has bonded well to the old snow surfaces on most protected N-NE-E aspects. Sunday's strong N-NE-E winds stripped most of the new snow away from any of these aspects that were exposed to the wind redeposited it onto NW-W-SW-S-SE slopes on top of a mix of bare ground, hard melt freeze crusts and wind scoured surfaces. The transport made the new snow more cohesive and has formed soft slabs on these aspects.

The soft slabs and storm snow will continue to be a concern today because both are most prevalent on the slopes that will be most affected by the continued rapid increase in temperature and strong March sun. This upper most layer of snow has not been through any melt/freeze cycles. It has not formed channels that would allow the newly formed free water to drain through the new snow layer. This free water could saturate the new snow layer and could weaken it to the point of failure. Over the next few days as the new snow undergoes more melting and refreezing this instability should become less of a problem. Yesterday in the Mt. Rose area several natural point release avalanches were observed near and above treeline on SE and NW facing aspects. Today similar human triggered avalanche activity is possible on steep, sun exposed slopes where new snow sits on top of a hard old snow surface. It should start out as pinwheels and point release slides but could progress to slab avalanches as the day warms up. Natural activity could become possible on heavily wind loaded, steep, sun exposed slopes that had previous snow cover. These instabilities should not form on the N-NE-E aspects near and above treeline due to heavy scouring of the snow surface, colder temperatures, and less sun exposure.

The bottom line: The avalanche danger is MODERATE at all elevations on all sun exposed aspects, 37 degrees and steeper that have significant storm snow on them. Isolated pockets of CONSIDERABLE danger could develop on the most heavily wind loaded, sun exposed slopes at all elevations. Steep cross loaded NW and SE facing gullies and wind loaded SW-W slopes will be the most suspect.
Public donations to the avalanche center this season are below our fundraising goal. We are going to raffle a beacon, shovel, probe, and backpack package as a way give back to those who donate $100 or more before March 30th. For more information on the raffle and amount of donations received click here.

Andy Anderson, Avalanche Forecaster

Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet): 31 deg. F
Max. temperature at Sierra Crest past 24 hours: 36 to 40 deg. F.
Average wind direction at Sierra Crest past 24 hours: Northeast shifting to the west after 4pm yesterday
Average wind speed at Sierra Crest past 24 hours: 25 mph while out of the northeast then 5 mph after shifting to the west.
Maximum wind gust at Sierra Crest past 24 hours: 57 mph
New snowfall at 8,200 feet past 24 hours: 0 inches
Total snow depth at 8,200 feet: 86 inches
Mountain Weather Forecast For Today:
Mostly sunny with more clouds developing overnight.
Temperature forecast for 8,000 to 9,000 feet: 38 to 44 deg. F
Ridgetop winds forecast for the Sierra Crest: West at 10 mph.
Snowfall expected in the next 24 hours: 0 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, Mostly sunny with more clouds developing overnight. Daytime highs 44 to 52 deg. F. West winds at 10 mph.

Tonight, mostly cloudy skies with overnight lows around 28 deg. F. Southwest winds at 10 to 15 mph with gusts to 25 mph.

For Wednesday, mostly cloudy skies with a chance of isolated snow showers in the afternoon. Daytime highs 39 to 47 deg. F. Southwest winds at 15 to 20 mph increasing to 20 to 30 mph with gusts to 45 mph in the afternoon.

Above 8000 Feet:
Today, Mostly sunny with more clouds developing overnight. Daytime highs 38 to 44 deg. F. West winds at 10 mph.

Tonight, mostly cloudy skies with overnight lows around 27 deg. F. Southwest winds at 10 to 15 mph with gusts to 25 mph.

For Wednesday, mostly cloudy skies with a chance of isolated snow showers in the afternoon. Daytime highs 33 to 39 deg. F. Southwest winds at 25 to 35 mph with gusts to 45 mph.


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.