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 January 30, 2008 7:00 AM
Click here for a detailed map of the SAC forecast area

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Today's Advisory:

Near and above treeline, avalanche danger is CONSIDERABLE with areas of HIGH danger on heavily wind loaded N-NE-E aspects, 35 degrees and steeper. Below treeline, avalanche danger is LOW. with isolated pockets of MODERATE danger on open wind loaded slopes 37 degrees and steeper.

As the cold front moves east of the forecast area, the winds should start to decrease, temperatures should increase, and there should be a break in the snowfall. By this afternoon most of the snow showers should have tapered off. Even with the forecasted decrease in wind speed today, the winds should still be strong enough to transport snow. The next system should start to affect the forecast area tonight. Initially the winds should increase again with sustained wind speeds reaching 70 to 90 mph with gusts to 125 mph above 8000 ft. by tomorrow afternoon. This system has more moisture associated with it, and snow totals in the Sierra could reach a foot or more by Friday morning.

In the last 24 hours 12 to 14 inches of new low density snow fell along the Sierra Crest. The Mount Rose area received about 5 inches of even colder, lighter snow. The winds continued to blow mostly from the southwest and increased over the course of the yesterday. Sensors along the Sierra Crest recorded sustained wind speeds greater than 75mph from 4pm through 9pm yesterday with gusts as high as 146mph! Overnight the winds started to decrease some, but they still averaged between 50 and 55 mph. These high winds caused wind loading farther downslope and helped to create larger stiffer wind slabs in some areas. The winds should continue to transport snow all day today as well. They should shift more to the west and decrease some today. As a result of these changes, they will again start to load the upper areas of the avalanche start zones and start to cross load some avalanche start zones. Wind slabs will have formed in the lower, upper, and side regions of some avalanche start zones. As these slabs start to connect and grow in size, the potential size of avalanches will also grow. The combination of new snow, continued wind transport, and the continued presence of weak layers (new snow weaknesses, a density inversion, and deeper persistent weaknesses) in the snowpack will keep the avalanche danger from decreasing today.

Near and above treeline yesterday in the Mount Judah backcountry several N-NE-E facing test slopes failed easily in response to the weight of a skier. One natural D2 avalanche was observed in the upper NE facing bowl on Mt. Judah. All of these failures occurred in the new snow on the top of the more dense layer of snow that fell earlier this week. Large, tender cornices that could be easily triggered well away from the edge of the cornice were also observed. In the Mount Rose area, ski patrol reported several D1 stiff slabs releasing during control work in response to ski cutting. These slabs released on a lighter layer of new snow just below the stiff wind slab. Below treeline on Waterhouse Peak and on Jake's Peak good bonding within the upper snowpack and minimal slab formation was reported in the trees. Excellent snow conditions were also reported in those areas.

Today human triggered avalanche activity and cornice failure continues to be probable near and above treeline. On the most heavily wind loaded and corniced N-NE-E slopes steeper than 35 degrees human triggering of avalanches is likely and some natural activity may occur.Be wary of wind loaded areas where there is a stiff slab on the surface with softer snow below. These hard slabs should be more difficult to trigger; however, if they do break they are more likely to break well above the person who triggers them making escape extremely hard and burial much more likely. It is easy to find out if this is the case by probing with a ski pole or digging a quick hand pit. This configuration sometimes sounds hollow as well. In some isolated areas where wind loading has been the heaviest and the old weak layers are the weakest, these avalanches have the potential to start in the newest storm snow and step down to the crust layers and facets that existed on the snow surface before it started snowing last week. This would result in large, deep, destructive avalanches. Due to the variability of distribution of both these weak layers and the wind slabs, these areas will be hard to predict without digging into the snow to test the weak layers. Below treeline human triggered avalanche activity is much less likely due to less slab formation and stronger bonding in the upper snowpack. On isolated slopes that are steep, heavily wind loaded, and open it may be possible for a human triggered avalanche to occur.
The bottom line: Near and above treeline, avalanche danger is CONSIDERABLE with areas of HIGH danger on heavily wind loaded N-NE-E aspects, 35 degrees and steeper. Below treeline, avalanche danger is LOW. with isolated pockets of MODERATE danger on open wind loaded slopes 37 degrees and steeper.

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): 10 deg. F
Max. temperature at Sierra Crest past 24 hours: 15 deg. F
Average wind direction at Sierra Crest past 24 hours: Southwest
Average wind speed at Sierra Crest past 24 hours: 55-60 mph
Maximum wind gust at Sierra Crest past 24 hours: 146 mph
New snow fall at 8,200 feet past 24 hours: 12 inches
Total snow depth at 8,200 feet: 87 inches
Mountain Weather Forecast For Today:
Mostly cloudy with snow showers in the morning and tapering off this afternoon.
Temperature forecast for 8,000 to 9,000 feet: 10 to 15 deg. F
Ridgetop winds forecast for the Sierra Crest: West 40 to 60 mph with gusts to 80 mph decreasing to 20 to 30 mph with gusts to 50 mph in the afternoon.
Snowfall expected in the next 24 hours: 1 to 2 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, mostly cloudy with snow showers in the morning and tapering off this afternoon. Snow accumulation 1 to 2 inches. Daytime highs 15 to 25 deg. F. Southwest winds at 10 to 20 mph with gusts to 30 mph.

Tonight, mostly cloudy skies. Overnight lows 15 to 20 deg. F and warming to 21 to 26 deg. F after midnight. Southwest winds at 10 to 20 mph with gusts to 30 mph.

For Thursday, snow with accumulations of 4-8 inches. Daytime highs 25 to 30 deg. F. West winds at 15 to 25 mph with gusts to 45 mph.

Above 8000 Feet:
Today, mostly cloudy with snow showers in the morning and tapering off this afternoon. Snow accumulation 1 to 2 inches. Daytime highs 10 to 15 deg. F. West winds at 40 to 60 mph with gusts to 80 mph decreasing to 20 to 30 mph with gusts to 50 mph in the afternoon.

Tonight, mostly cloudy skies. Overnight lows 10 to 15 deg. F and warming to 18 to 23 deg. F after midnight. West winds at 25 to 35 mph with gusts to 75 mph.

For Thursday, snow with accumulations of 5-10 inches. Daytime highs 21 to 26 deg. F. West winds at 40 to 55 mph with gusts to 85 mph, increasing to 70 to 90 mph with gusts to 125 mph in the 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:
	Wednesday:	Wednesday Night:	Thursday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.