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.

Another storm system is moving into the forecast area this morning. While this storm system is weaker than the systems of the past several days, a short period of significant snowfall is expected to occur during the morning hours before tapering to snow showers sometime this afternoon. New snow amounts for the past 24 hours are running 5 to 15 inches across the forecast area with 2 to 7 inches from the past 12 hours. An additional 8 to 14 inches is expected to accumulate today. Snow showers are expected to continue through tomorrow. Ridgetop winds remain out of the southwest. Moderate to strong wind speeds for today are expected to continue through tomorrow.

Observations:

Observations were made yesterday in two locations in the Mount Rose region. Above Crystal Bay, evidence of a small natural avalanche that likely occurred around sunrise was visible at 7,360' on a wind loaded E aspect 34 degree slope in near treeline terrain. Crown depth measured 12 to 14 inches. The avalanche was fairly narrow, but ran 250' to 300' vertical feet. Evidence of two other similar avalanches in similar terrain nearby were mostly snowed over, indicating that they had likely occurred the previous afternoon or evening. Moderate skier triggered cracking and fragile cornices were noted in the area. Snowpit data collected near the most recent avalanche yielded little additional evidence of ongoing instability (photos, pit profile, more info).

On Tamarack Peak, shooting cracks were common in wind loaded and moderately wind affected areas above and below treeline. Instability was noted on both a layer of rimed crystals 10 to 20 cm below the snow surface and slightly deeper on a density inversion 30 cm below the snow surface. Cracking occurred on one weak layer or the other in various locations with no real pattern to differentiate. Test slope slab failure triggered by intentional cornice collapse occurred at 9,800' on a NE aspect 40 degree slope in near treeline terrain. The slab failed on a thin weak layer of rimed crystals 10cm above a significant density change to lower density snow. The slab and bed surface were both 4F hard with no easily discernible difference. Slab thickness was 10 to 20 cm. Significant graupel 2-3mm in size was observed falling from the sky and accumulating on the snow surface in this area from 1pm to 3:30pm. Several inches of settlement were noted around trees in this area during the afternoon hours. (photos, more info).

Avalanche Concern #1: Wind Slabs

Continued wind transport of snow yesterday combined with new snow and wind last night and today will keep the concern for unstable wind slabs ongoing. Widespread cracking that was observed yesterday is expected to continue today in wind loaded areas both above and below treeline. Near and above treeline areas on NW-N-NE-E-SE-S aspects will hold the greatest instability today. This same instability will carry over into wind loaded below treeline areas as well. Snowpack failure up to several feet deep within the recent storm snow is possible as several wind slabs are now stacked one on top of another. The best window for natural avalanche activity will occur this morning while snowfall rates are higher. Human triggered avalanches will remain possible to likely all day long.

Avalanche Concern #2: Storm Snow Weaknesses

Density changes, lightly rimed snow crystals, and heavily rimed snow crystals know as graupel that exist within the upper portion of the snowpack are expected to create ongoing instability in both wind affected and wind protected areas. Slab failure is expected in wind affected areas while loose snow avalanches or sluffs are expected in wind protected areas. This instability is expected to remain limited to the top 1 to 2 feet of the snowpack. Avalanche activity that fails on storm snow weaknesses today is expected to be human triggered and may occur on any aspect near treeline or below treeline.

 

The bottom line:

Near and above treeline, avalanche danger is CONSIDERABLE on NW-N-NE-E-SE-S aspects on slopes 35 degrees and steeper. Below treeline avalanche danger is MODERATE with pockets of CONSIDERABLE danger on NW-N-NE-E-SE-S aspects on slopes 35 degrees and steeper. On the SW-W aspects avalanche danger is MODERATE both above and below treeline on slopes 35 degrees and steeper. Large and destructive avalanches remain possible. The best window for natural avalanche activity will occur during the morning hours. Human triggered avalanches will remain possible to likely all day long.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

Weather Observations from along the Sierra Crest between 8200 ft and 8800 ft:

0600 temperature:	18 to 22 deg. F.
Max. temperature in the last 24 hours:	21 to 26 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	54 mph
Maximum wind gust in the last 24 hours:	93 mph
New snowfall in the last 24 hours:	5 to 15 inches
Total snow depth:	137 to 208 inches

Two-Day Mountain Weather Forecast - Produced in partnership with the Reno NWS

For 7000-8000 ft:
	Saturday:	Saturday Night:	Sunday:
Weather:	Cloudy skies with snow.	Mostly cloudy skies with a chance of snow showers.	Mostly cloudy skies with a chance of snow showers.
Temperatures:	25 to 32 deg. F.	15 to 25 deg. F.	29 to 35 deg. F.
Wind direction:	SW	SW	SW
Wind speed:	30 to 40 mph with gusts to 65 mph.	30 to 40 mph with gusts to 65 mph. Winds decreasing to 25 to 30 mph with gusts to 55 mph after midnight.	15 to 20 mph with gusts to 40 mph. Winds increasing to 20 to 30 mph with gusts to 60 mph in the afternoon.
Expected snowfall:	8 to 12 in.	0 to trace in.	Up to 2 in.
For 8000-9000 ft:
	Saturday:	Saturday Night:	Sunday:
Weather:	Cloudy skies with snow.	Mostly cloudy skies with a chance of snow showers.	Mostly cloudy skies with a chance of snow showers.
Temperatures:	20 to 27 deg. F.	13 to 20 deg. F.	23 to 30 deg. F.
Wind direction:	SW	SW	SW
Wind speed:	45 to 60 mph with gusts to 85 mph.	45 to 65 mph with gusts to 85 mph. Winds decreasing to 25 to 35 mph with gusts to 60 mph after midnight.	25 to 30 mph with gusts to 50 mph. Winds increasing to 35 to 45 mph with gusts to 65 mph in the afternoon.
Expected snowfall:	8 to 14 in.	0 to trace in.	Up to 2 in.