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 Monday, April 23rd, 2007 at 7:00 am

The bottom line: Near and above treeline the avalanche danger is MODERATE on windloaded aspects 35 degrees and steeper. As the east winds blow today the aspects that are the most suspect will shift from the previously windloaded N-NE-E aspects that are now being scoured to the NW-W aspects that are being newly loaded. Pockets of MODERATE avalanche danger could also form on cross-loaded SE slopes steeper than 35 degrees where there was snow cover previous to this storm. Below treeline the avalanche danger is LOW. Near and above treeline human triggered avalanche activity is still possible today. Use safe travel techniques and avoid steep heavily windloaded terrain.

The storm has abated and the skies are clearing. The north and east winds started blowing last night as the sun set and should become more intense and continue through today. This north and easterly flow should allow the area to stay cooler today even as a high pressure ridge builds over the forecast area. By tomorrow the ridge should be well established and should bring plenty of sunshine and warm temperatures. By then the winds should have calmed some and shifted back to the south and west.

Storm totals across the forecast area range from 16 - 22 inches of new snow in the last 48 hours. Cornices and windslabs formed on most of the N-NE-E aspects near and above treeline yesterday due to the strong, steady southwest winds during the storm. As the winds shifted to the north and east last night these cornices and windslabs started to be scoured away. This scouring by the east winds will cause the size and extent of these windslabs to decrease throughout the day. The snow that the east winds transport away from the N-NE-E aspects will be redeposited on the NW-W-SW aspects. On the NW and W aspects where there was snow cover previous to this storm, this wind transported snow will form new windslabs on top of the old melt-freeze surface. This surface was a hard, frozen melt freeze crust before the storm, and it was scoured by the wind during the storm making it even harder. Bonding between this surface and the newly formed windslabs will be suspect today. On the W-SW-S aspects where there was hardly any snow before the storm, the wind transported snow will be deposited onto a surface with plenty of exposed anchors that should prevent most avalanche activity.

Any avalanche activity that occurs today is expected to involve windslabs newly formed by the east winds and maybe some isolated pockets of windslabs formed during the storm that have not yet been destroyed by east wind scouring. Avalanches could step down to the old melt-freeze crust in some areas. Snowpack failure occurring below the height of the uppermost melt-freeze crust in the snowpack is not expected at this time. The most significant avalanche activity should occur on recently windloaded slopes that are steeper than 35 degrees near and above treeline.

Yesterday several natural R1 D1-D2 soft slab avalanches were observed. Some on the northeast face of Donner Peak starting above the train tunnel on 40-45 degree slopes and some on the east face of Mt. Judah at 8000' starting on 38-45 degree slopes. One R1 D2 soft slab was remotely triggered by a skier 200 standing yards away on the ridgeline of Mt. Judah. Crowns on these slides ranged from 1-2 feet deep and 20 to 40 yards wide. They ran anywhere from 100-300 yards downslope.

Human triggered avalanches are still possible in recently wind loaded areas above treeline. Use clues like drifted snow, cornices, blowing snow, and ripples in the snow surface to determine which slopes are the most windloaded. Enjoy these last days of winter carefully: use terrain to manage your exposure to avalanche hazard toady and as always use safe backcountry travel techniques.

The bottom line: Near and above treeline the avalanche danger is MODERATE on windloaded aspects 35 degrees and steeper. As the east winds blow today the aspects that are the most suspect will shift from the previously windloaded N-NE-E aspects that are now being scoured to the NW-W aspects that are being newly loaded. Pockets of MODERATE avalanche danger could also form on cross-loaded SE slopes steeper than 35 degrees where there was snow cover previous to this storm. Below treeline the avalanche danger is LOW. Near and above treeline human triggered avalanche activity is still possible today. Use safe travel techniques and avoid steep heavily windloaded terrain.

This advisory will be the last avalanche advisory of the 2006-2007 season. Thanks you to everyone who made this season possible. We plan to stop issuing danger ratings Tuesday and to start issuing a snow conditions update instead. We plan to end operations for the season on April 28th.

Thank you to all of our sponsors, those individuals who purchased tickets for the SAC Ski Day fundraising events, and everyone else who donated funding this winter. We have met our operating budget for this season and have a solid start on next year's funding. For more details about our financial situation please click here.

Andy Anderson, Avalanche Forecaster
Today's Central Sierra Weather Observations:
0600 temperature at Sierra Crest (8,700 feet):
24 deg. F
Max. temperature at Sierra Crest past 24 hours:
29 deg. F
Average wind direction at Sierra Crest past 24 hours:
Southwesterly shifting to the east after 10 pm yesterday
Average wind speed at Sierra Crest past 24 hours:
30 mph
Maximum wind gust at Sierra Crest past 24 hours:
57 mph
New snow fall at 8,200 feet past 24 hours:
6-8 inches
Total snow depth at 8,200 feet:
72 inches
Mountain Weather Forecast For Today:
Partly cloudy this morning and clearing this afternoon.
Temperature forecast for 8,000 to 9,000 feet:
28 - 38 degrees F.
Ridgetop winds forecast for the Sierra Crest:
Northeast at 25 - 35 mph, gusting to 50 mph.
Snowfall expected in the next 24 hours:
0 inches
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, partly cloudy with daytime highs 35 to 45 degrees F. Northeast winds at 10 to 20 mph. Tonight, clear skies with overnight lows 30 to 40 degrees F. North winds at 5 to 15 mph. Tuesday, sunny with daytime highs 45 to 55 degrees F. West winds at 5 to 15 mph are expected.

Above 8000 Feet:
Today, partly cloudy with daytime highs 28 to 38 degrees F. Northeast winds at 25 to 35 mph with gusts to 50 mph. Tonight, clear skies with overnight lows 24 to 34 degrees F. North winds at 10 to 20 mph. Tuesday, sunny with daytime highs 42 to 52 degrees F. West winds at 10 to 20 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:
	Monday:	Monday Night:	Tuesday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Monday:	Monday Night:	Tuesday:
Weather:
Temperatures:	deg. F.	deg. F.	deg. F.
Wind direction:
Wind speed:
Expected snowfall:	O in.	O in.	O in.