THIS AVALANCHE FORECAST EXPIRED ON January 7, 2019 @ 7:01 am
Avalanche Forecast published on January 6, 2019 @ 7:01 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

CONSIDERABLE avalanche danger will exist at all elevations this morning due to wind slab and storm slab avalanche problems. The avalanche danger will increase to HIGH around midday as a second storm impacts the forecast area bringing blizzard conditions. HIGH danger will last through the night. Travel in avalanche terrain is not recommended.

4. High

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Above Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

4. High

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Near Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

4. High

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Below Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
    Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
Avalanche Problem 1: Wind Slab
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Strong winds and more than a foot of new snow have already formed fragile wind slabs on many leeward slopes. These wind slabs will become much larger and more widespread in the next 24 hours with more gale force winds and another few feet of snow forecasted to start later this morning. Near and above treeline NW-N-NE-E-SE aspects will hold the largest wind slabs, but wind slabs could also exist in wind-loaded areas below treeline. In many areas especially along the Sierra Crest, these wind slabs rest on top of weak old snow layers. Failure of these layers could allow remote triggering and/or wider propagation with avalanches possibly wrapping around corners and across adjacent avalanche paths.    

Triggering a wind slab avalanche will be likely this morning and become very likely this afternoon and during the night. Some large natural wind slab avalanches could become likely as well. Large destructive avalanches could occur. Travel in avalanche terrain is not recommended.

Avalanche Problem 2: Storm Slab
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Rapid accumulation and changing conditions during the storm last night may have left sensitive storm slabs on steep sheltered slopes. More snow starting later this morning and continuing through the night will exacerbate the storm slab problem. In cases where these storm slabs form above old weak snow, they could exhibit some persistent slab characteristics and be easier to trigger and propagate across larger areas when they fail.  

Storm slab avalanches could become very likely in the next 24 hours especially during times when snowfall rates reach or exceed 2 inches per hour. Travel in avalanche terrain is not recommended.

 

recent observations

* Observations along the Sierra Crest this week have shown weak layers (weak facets and thin crusts) in the upper snowpack that may not handle new snow loading well. Yesterday afternoon on Becker Ridge, some ski-triggered cracking started to occur as soon as new snow started to accumulate on these weak layers.

* The snowpack in the Mt. Rose area (Carson Range) lacks these crusts and appears in decent condition to handle new snow loading. Shallower, weaker snow has been noted further south along the Carson Range closer to Freel and Jobs Peaks.

Weather and CURRENT CONDITIONS
weather summary

Since midday yesterday, most remote sensors along the Sierra Crest have received 10 to 15 inches of new snow with Donner Summit and Ebbetts Pass gaining 16 to 17 inches. On the east side of Lake Tahoe, sensors reported 8 to 10 inches of new snow. Snow showers should diminish some this morning as the first of the series of storms departs the area. A second storm should arrive over the region by late morning bringing an end to the brief weather respite. Intense snowfall and gale force southwest winds will return to the region and should last through the night. The forecast calls for snowfall rates of more than 2 inches per hour at times and total new snow accumulations of ~1.5 to 3 ft. above 7000 ft by tomorrow. For more details check in with the Reno NWS.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 16 to 22 deg. F.
Max. temperature in the last 24 hours: 28 to 34 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 45 to 55 mph
Maximum wind gust in the last 24 hours: 99 mph
New snowfall in the last 24 hours: 10 to 17 inches
Total snow depth: 39 to 47 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 90%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 95%. Mostly cloudy. Snow showers likely. Snow levels below 7000 feet. Chance of precipitation is 70%.
Temperatures: 27 to 32 deg. F. 26 to 31 deg. F. 35 to 40 deg. F.
Mid Slope Winds: Southwest 15 to 30 mph. Gusts up to 50 mph increasing to 70 mph in the afternoon. South 25 to 35 mph with gusts to 80 mph shifting to the southwest 30 to 45 mph with gusts to 90 mph after midnight. Southwest 20 to 35 mph. Gusts up to 90 mph decreasing to 65 mph in the afternoon.
Expected snowfall: 70% probability of 6 to 10 inches. 30% probability of 10 to 14 inches. | SWE = 0.30-0.55 inch. 80% probability of 10 to 18 inches. 20% probability of 18 to 24 inches. | SWE = 0.75-1.25 inches. 80% probability of 2 to 4 inches. 20% probability of 4 to 6 inches. | SWE = up to 0.30 inch.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 90%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 95%. Mostly cloudy. Snow showers likely. Snow levels below 7000 feet. Chance of precipitation is 70%.
Temperatures: 24 to 29 deg. F. 22 to 27 deg. F. 32 to 37 deg. F.
Ridge Top Winds: Southwest 30 to 50 mph with gusts to 95 mph. South 50 to 70 mph shifting to the southwest 60 to 75 mph after midnight. Gusts up to 120 mph. Southwest 35 to 55 mph. Gusts up to 95 mph decreasing to 70 mph in the afternoon.
Expected snowfall: 70% probability of 6 to 10 inches. 30% probability of 10 to 16 inches. | SWE = 0.30-0.55 inch. 80% probability of 10 to 18 inches. 20% probability of 18 to 24 inches. | SWE = up to 1.45 inches. 80% probability of 2 to 4 inches. 20% probability of 4 to 6 inches. | SWE = up to 0.40 inch.
Disclaimer

This avalanche forecast is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This forecast 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 forecast applies only to backcountry areas outside established ski area boundaries. This forecast describes general avalanche conditions and local variations always occur. This forecast expires 24 hours after the posted time unless otherwise noted. The information in this forecast is provided by the USDA Forest Service who is solely responsible for its content.

For a recorded version of the avalanche forecast call (530) 587-3558 x258