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.

Snowfall started around midnight last night. Since then 4-6 inches of new snow has accumulated above 7000 ft. Strong southwest winds that averaged 35-45 mph with gusts as high as 102 mph accompanied this snowfall. Snow should continue today with the most intense periods of snowfall occurring this morning and last night. The forecast calls for another 3-6 inches of snow above 7000 ft. today. The strong southwest winds should also persist through today. As the low pressure moves out of the area over the next 24 hours, unsettled showery weather should continue, but the without much additional accumulation tonight and tomorrow. As snowfall decreases, the wind strength should also diminish and start shifting to the south and east. By tomorrow afternoon the forecast calls for southeast winds at less than 15 mph. Temperatures should remain in the upper teens and 20's for today and tomorrow with overnight lows in the low to mid teens.

Recent Observations:

Yesterday observations on Andesite Peak showed that the existing snowpack should handle the new snow load well (photos, snowpit, more info). Some possible weak layers did exist within the upper 6-8 inches of the snowpack. Tests on these layers indicated that even if they do break, the resulting fractures should not travel very far. Some minor wind transport had also occurred and formed wind slabs less than 3 inches thick in this area yesterday morning. The warm temperatures and cloud cover had allowed a thin breakable melt-freeze crust to form on the surface on many slopes below 8200 ft. in this area yesterday. Softer snow existed below this crust in sheltered areas, and the crust did not exist in areas where the thin wind slabs had formed.

Avalanche Problem #1: Wind Slabs

Human-triggered avalanches involving newly formed wind slabs will be likely today and natural avalanches will be possible. These wind slabs started forming on the wind loaded aspects last night due to the new snow and strong consistent southwest winds. As the storm continues today, these slabs will become larger and more widespread. These slabs sit on a mix of old snow surfaces ranging from soft unconsolidated snow to thin crusts to thin wind slabs. The new slabs have not had time to form strong bonds with these old snow surfaces. Wind loaded N-NE-E aspects and cross loaded NW and SE aspects in near and above treeline areas will hold the largest and most fragile wind slabs. Some smaller wind slabs may also exist on those aspects in below treeline areas due to the strength of the winds. Most avalanches involving these winds slabs should only involve the new snow; however, some of them may entrain the top few inches of the older snow.

Avalanche Problem #2: Storm Slabs

In non-wind affected areas, changing storm conditions and rapid accumulation may have created both soft storm slabs and some storm snow weaknesses. These storm slabs will also rest on similar old snow surfaces as the wind slabs mentioned above. Human-triggered avalanches involving these storm slabs will be possible today and could be likely in a few areas that receive the most snow. These storm slabs could exist on any sheltered slopes. 

Avalanche Problem #3: Loose Snow Avalanches

Cold new snow accumulating above a thin melt freeze crust and on storm snow weaknesses within the new snow will allow human-triggered loose dry snow avalanches to occur today on steep slopes. Some of these sluffs could entrain enough snow to knock a person off his/her feet or push a person into a terrain trap.

 

The bottom line:

Near and above treeline the avalanche danger is CONSIDERABLE on NW-N-NE-E-SE aspects on slopes steeper than 35 degrees due to new snow and wind forming unstable wind slabs. Below treeline pockets of CONSIDERABLE danger exist on those same aspects due to fragile soft storm slabs and some wind slabs. Human-triggered avalanches are likely today and natural avalanches are possible.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	20-26 deg. F.
Max. temperature in the last 24 hours:	33-40 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	35-45 mph
Maximum wind gust in the last 24 hours:	102 mph
New snowfall in the last 24 hours:	4-6 inches
Total snow depth:	57-87 inches

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

For 7000-8000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Cloudy with snow showers	Cloudy with numerous snow showers in the evening. Snow showers becoming scattered after midnight.	Cloudy with a chance of snow showers
Temperatures:	25-30 deg. F.	10-15 deg. F.	21-27 deg. F.
Wind direction:	Southwest	Southwest	Southeast
Wind speed:	20-35 mph with gusts to 60 mph	15-25 mph with gusts to 40 mph decreasing to 10-20 mph with gusts to 30 mph after midnight	10-15 mph in the morning decreasing in the afternoon
Expected snowfall:	3-6 in.	up to 2 in.	up to 2 in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Cloudy with snow showers	Cloudy with numerous snow showers in the evening. Snow showers becoming scattered after midnight.	Cloudy with a chance of snow showers
Temperatures:	21-27 deg. F.	8-13 deg. F.	19-24 deg. F.
Wind direction:	Southwest	Southwest shifting to the south after midnight	Southeast
Wind speed:	50-60 mph with gusts to 95 mph decreasing to 85 mph in the afternoon	35-40 mph with gusts to 60 mph decreasing to 25-30 mph with gusts to 45 mph after midnight	15-20 mph with gusts to 30 mph decreasing in the afternoon
Expected snowfall:	3-6 in.	up to 2 in.	up to 2 in.