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 7, 2008 6:54 AM
Click here for a detailed map of the SAC forecast area

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Today's Advisory:
Near and above treeline the avalanche danger is CONSIDERABLE on NW-N-NE-E aspects, 35 degrees and steeper. Below treeline, avalanche danger is MODERATE with pockets of CONSIDERABLE in open areas steeper than 35 degrees.

The forecast calls for periods of sun again today as the low pressure system moves off to the east. Some snow showers may occur along the western edge of the Sierra Crest, but they should not produce much measurable precipitation.The southwest winds should diminish some today before picking back up again as another system approaches tonight. This system should pass mostly to the north of the forecast area and only bring some small accumulation to the mountains. It will cause the southwest winds to increase again and should bring more clouds to the area tonight and tomorrow. The air temperatures should stay cold today before warming slightly tomorrow as the new system impacts the area.

Over the last 24 hrs. 2 to 4 inches of new snow fell on the Sierra Crest and 1 to 2 inches in the Mount Rose area. Even though snowfall decreased and there should be no appreciable new accumulation today, the winds have been transporting snow and wind loading slopes since Thursday night. This wind loading continued yesterday and the winds should still be strong enough today to wind load leeward slopes.The winds have been shifting from the SSW to SW to WSW through out the storm. These winds continue to form wind slabs on the NW-N-NE-E aspects and large cornices on the lee side of ridgelines. The largest wind slabs and cornices formed near and above treeline; however, strong winds early in the storm also formed wind slabs in open areas below treeline. These winds slabs and cornices should still be sensitive to human triggering today.

Weaknesses (small density changes, changes in snow crystal type, and rimed snow crystals-like graupel) that formed in the upper layers of the new snow as a result of subtle changes in the storm's winds, snowfall intensity, and temperature do exist under these windslabs. Several human triggered avalanches occurred on these layers yesterday. On Mt. Judah yesterday 3 intentionally triggered soft slab avalanches occurred. 1 was triggered by a ski cut on a NE facing 34 degree slope at 7700' in an open area below treeline. Another one on a 33 degree NNE facing slope was triggered with a oven size cornice piece at 7200'. The third one was triggered by a smaller cornice (mini-fridge size) piece on a 34 degree ENE facing slope above treeline. Mt. Rose Ski Patrol reported that ski cutting and simply approaching slopes on skis released several avalanches on similar weak layers during the morning's control work. All of these slides had crowns ranging from 8-16 inches. The continued wind loading and colder than normal air temperatures should cause these weaknesses to take longer than usual to consolidate especially at the higher elevations. These weaknesses should still be active today. They should strengthen as the new snow settles over the next few days. There has been no activity on the the weak layers present at the base of the storm snow (the density inversion and the rain crust) or on the weak layers deeper in the snowpack (old crusts and basal facets). These layers will be hard to trigger since they are buried so deeply; however, failure in these layers is not impossible.

The majority of avalanche activity should occur within the new snow on wind loaded slopes. Any avalanches that do occur today could also step down to near the old/new snow interface where a density inversion, a melt-freeze crust, a wind crust, or near surface faceted snow crystals exist, depending on location. Snowpack failure into the basal faceted layer at ground level is still a possibility, especially once a large avalanche is already in motion.
Near and above treeline human triggered avalanches are probable today on all wind loaded slopes steeper than 35 degrees. NW-N-NE-E aspects will be the most likely to wind load from the southwest wind. Natural avalanches are still possible on these slopes as well. Below treeline, natural avalanches are possible on any open slopes steeper than 35 degrees. Human triggered avalanche are probable in these areas as well.

The bottom line: Near and above treeline the avalanche danger is CONSIDERABLE on NW-N-NE-E aspects, 35 degrees and steeper. Below treeline, avalanche danger is MODERATE with pockets of CONSIDERABLE in open areas steeper than 35 degrees.

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): 13 deg. F
Max. temperature at Sierra Crest past 24 hours: 116 deg. F
Average wind direction at Sierra Crest past 24 hours: Southwest
Average wind speed at Sierra Crest past 24 hours: 38 mph
Maximum wind gust at Sierra Crest past 24 hours: 88 mph
New snow fall at 8,200 feet past 24 hours: 1 to 4 inches
Total snow depth at 8,200 feet: 62-72 inches
Mountain Weather Forecast For Today:
Partly cloudy this morning becoming mostly cloudy with snow showers in the afternoon and evening.
Temperature forecast for 8,000 to 9,000 feet: 19 to 23 deg. F
Ridgetop winds forecast for the Sierra Crest: Southwest at 15 to 25 mph with gusts to 45 mph shifting to the west this afternoon.
Snowfall expected in the next 24 hours: 1 inch
2 Day Mountain Weather Forecast:

7000 to 8000 Feet:
Today, partly cloudy this morning becoming mostly cloudy with snow showers in the afternoon and evening. Daytime highs 23 to 27 deg. F. Southwest winds at 10 to 15 mph, with gusts to 25 mph shifting to the west this afternoon.

Tonight, cloudy skies with a chance of snow showers. Snow accumulation less than 1 inch. Overnight lows 13 to 17 deg. F. Southwest winds at 10 to 15 mph with gusts to 25 mph.

For Tuesday, snow showers with accumulation of 4 to 8 inches. Daytime highs 28 to 24 deg. F. Southwest at 10 to 25 mph with gusts to 45 mph.

Above 8000 Feet:
Today, partly cloudy this morning becoming mostly cloudy with snow showers in the afternoon and evening. Daytime highs 19 to 23 deg. F. Southwest winds at 15 to 25 mph, with gusts to 45 mph shifting to the west this afternoon.

Tonight, cloudy skies with a chance of snow showers. Snow accumulation less than 1 inch. Overnight lows 9 to 15 deg. F. west winds at 15 to 25 mph with gusts to 55 mph.

For Tuesday, snow showers with accumulation of 5 to 10 inches. Daytime highs 26 to 30 deg. F. Southwest at 25 to 40 mph with gusts to 80 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:
	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.