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.

Over the last 24 hours temperatures have continued to fall dropping into the single digits in the Mt. Rose area and into the low teens above 8000 ft. along the Sierra Crest. After a period of intense snowfall yesterday morning, snow showers continued for the rest of the day and into the night with less intensity. Snowfall totals for the last 24 hours range from 16-24 inches with the southern and central parts of the forecast area receiving the highest amounts of snow. This brings storm totals to about 28-32 inches since Tuesday night. Due to the cold temperatures most of the last 24 hour's snow fell at a lower density (meaning lighter snow) than the snow from earlier in the storm. The southwest winds have remained between 45 mph and 55 mph with gusts as high as 105 mph along the crest.

After a brief lull in the storm today, another wave of winter weather should impact the forecast area this afternoon through tomorrow. This second storm should bring more snow, continued winds, and slightly warmer temperatures. The forecast calls for another 2-4 ft of new snow above 7000 ft by the end of the day tomorrow. The southwest winds should decrease some this morning before increasing again this afternoon.  They should remain slightly slower than the winds that have occurred over the past 24 hours with gusts only forecast to reach into the 80's along the crest.

Observations:

Several skier triggered avalanches occurred in both above and below treeline terrain on Hidden Peak yesterday afternoon. In the near and above treeline terrain, the avalanches that occurred did so on wind-loaded, 35-38 degree, N-NE aspects. These wind slabs failed and ran on a weakness within the storm snow 1-1.5 ft deep. Two of them were remotely triggered as far as 20-30 ft away from the actual slope. One of these slides fractured down to the old crust layer but did not run on it (photos, video, and more info). Ski cuts at the top of steep slopes triggered the soft slab avalanches that occurred below treeline on Hidden Peak. These slides occurred on steeper (38-40 degrees), E-NE facing aspects at about 8200 ft and also failed and ran on a storm snow weakness 1-1.5 ft deep (photos, more info). Prior to these slide several skier-triggered shooting cracks occurred both above and below treeline. Below treeline these cracks only extended 2-4 ft from the skiers. Above treeline they started to shoot up to 20-30 ft away. Observations and stability tests showed bonding within the new snow was slower than what is usual for the Sierra. This slower bonding is likely due to the colder temperatures. 

Primary Avalanche Concern: Wind Slabs

Wind slabs on leeward slopes have grown over the last 24 hours and should continue to grow during the next 24 hrs as more snow and wind impact the forecast area. The colder temperatures should make these slabs slower to bond to the various snow below them that could serve as weak layers. In areas where these wind slabs have not already slid, the added weight of a person would likely overload the bonds holding them in place resulting in a human-triggered avalanche. Natural avalanches will also remain possible especially later in the day as the addition of more snow to these slabs could provide a trigger for avalanche activity. These slabs could reach several feet in depth and step down onto the older crusts below them. They could also run long distances due to the hard bed surfaces that exist beneath them in some starting zones. The open wind-loaded N-NE-E and cross-loaded NW and SE aspects near and above treeline hold the best potential for this type of avalanche. However, these slabs could extend into traditionally sheltered areas and lower elevation slopes due to the strength of the winds during this storm. Use clues like blowing snow, cornices, drifts, ripples, and other wind created features to tell where wind-loading has occurred.

Avalanche Concern #2: Storm Snow Weaknesses

The weaknesses that have formed due to changes in the temperature, snowfall rate, and other conditions during the storm should also remain active today due to colder temperatures slowing down the settlement and consolidation processes. The addition of more new snow last night and today will also make it harder for those slow forming bonds to gain strength fast enough to keep pace with the increasing load. Human-triggered avalanches that fail due to those storm snow weaknesses will be likely today on open slopes 36 degrees and steeper even in below treeline terrain. In some areas that have received the most new snow, some natural activity may be possible. Soft slabs should comprise most of these avalanches.

Avalanche Concern #3: Loose Snow Avalanches

Cold temperatures and light, low density new snow will make loose snow avalanches the third avalanche concern again today. Human-triggered sluffs that entrain much of the new cold snow on the surface will remain possible on any steep slopes. Even though these slides are not likely to bury a person on their own, they could easily push someone into a terrain trap or add enough weight to the slope below to trigger a slab avalanche.

The bottom line:

Near and above treeline on slopes steeper than 35 degrees, CONSIDERABLE avalanche danger exists on the NW-N-NE-E-SE aspects. Below treeline on slopes steeper than 35 degrees, MODERATE avalanche danger exists on all aspects with pockets of CONSIDERABLE danger on NW-N-NE-E-SE aspects on slopes steeper than 37 degrees.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	11-14 deg. F.
Max. temperature in the last 24 hours:	Occurred yesterday at 6am: 17-22 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	45-55 mph
Maximum wind gust in the last 24 hours:	105 mph
New snowfall in the last 24 hours:	16-24 inches
Total snow depth:	81-116 inches

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

For 7000-8000 ft:
	Thursday:	Thursday Night:	Friday:
Weather:	Numerous snow showers in the morning becoming widespread snow this afternoon.	Snow	Snow
Temperatures:	18-22 deg. F.	18-22 deg. F.	24-27 deg. F.
Wind direction:	Southwest	Southwest	South
Wind speed:	15-25 mph with gusts to 35 mph	15-25 mph with gusts to 35 mph	10-15 mph with gusts to 30 mph increasing to 20-30 mph with gusts to 45 mph
Expected snowfall:	3-6 in.	6-12 in.	8-16 in.
For 8000-9000 ft:
	Thursday:	Thursday Night:	Friday:
Weather:	Numerous snow showers in the morning becoming widespread snow this afternoon.	Snow	Snow
Temperatures:	13-20 deg. F.	13-20 deg. F.	16-23 deg. F.
Wind direction:	Southwest	Southwest	South
Wind speed:	30-40 mph with gusts to 60 mph increasing to 40-50 mph with gusts to 80 mph in the afternoon	30-40 mph with gusts to 60 mph	20-35 mph with gusts to 60 mph increasing to 70 mph in the afternoon
Expected snowfall:	4-8 in.	8-16 in.	10-20 in.