THIS AVALANCHE FORECAST EXPIRED ON February 15, 2019 @ 6:59 am
Avalanche Forecast published on February 14, 2019 @ 6:59 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

HIGH avalanche danger exists at all elevations. Dangerous and complex avalanche conditions exist. Natural avalanches are likely and human-triggered avalanches are very likely. Large destructive avalanches could occur. Travel in, near or below avalanche terrain is not recommended. Rain on snow could also cause dangerous roof-avalanches under roofs that have not already unloaded.

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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New wind slabs have formed on wind-loaded slopes as a result of new snow and gale force winds. Near and above treeline NW-N-NE-E-SE aspects above 8000 ft where the most new snow has accumulated should hold the largest wind slabs. As snow levels drop today, additional snow and intense, pervasive winds will cause existing wind slabs to grow in size and new wind slabs to form at lower elevations and potentially in some below treeline areas. Large human-triggered wind slab avalanches remain very likely and natural wind slab avalanches are likely. In areas where rain falls on previously wind-loaded slopes, wind slab avalanches could involve wet snow and release more easily.

Avalanche Problem 2: Storm Slab
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Rapidly changing conditions during this storm have allowed weak layers and slab layers to form in the storm snow. Human-triggered storm slab avalanches remain very likely and natural storm slabs are likely. Storm slab avalanches could occur on any steep slopes on any aspect. Most storm slabs would involve the storm snow but some could entrain older snow especially in a few lower elevation areas on E-SE-S-SW aspects where a weak layer may exist near a thin crust. Until snow levels fall, rain falling on storm snow could weaken existing storm slabs and potentially result in larger avalanches that entrain some wet snow. As snow levels fall, new snow accumulation could cause new storm slabs to form at lower elevations.

Avalanche Problem 3: Loose Wet
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Rain falling on snow today will continue to make widespread loose wet avalanche activity very likely. Loose wet avalanches could entrain significant amounts of wet snow and become large enough to bury or injure a person. The rain will also continue to magnify and complicate the other avalanche problems. As snow levels fall today, this problem should start to diminish.

recent observations

* Yesterday several storm slab avalanches occurred on Andesite Peak. The weak layer was lower density storm snow that fell at the start of the storm and the slab was heavy wet snow above it. Skier-triggered shooting cracks, snowpit tests, and observations showed ongoing instability with this combination.

* Snow level hovered around 7000 ft until about 2 pm in the Donner Summit area yesterday. 

Weather and CURRENT CONDITIONS
weather summary

Snow levels stayed near lake level until about midday yesterday. Then they rose to between 8500 and 9000 ft by the end of the day. They remained high through the night. Overall 2.8 to 4.5 inches of water has fallen in the last 24 hours. Some sensors reported as much as 5-6 inches of water. It started as some snow then changed over to heavy rain in areas below 9000 ft. Heavy rain with snow levels between 8000 and 9000 ft should continue through the morning before cold air moves into the region. The forecast calls for snow levels to drop to below 7000 ft by late morning and down to lake level by this afternoon. Snow should continue through tomorrow with another 2 to 4+ ft accumulating by the end of the day on Friday depending on elevation. Gale force ridgetop winds with gusts in the 120 mph range should continue through tonight and mid slope winds should increase this afternoon. For more details on the current storm check in with the Reno NWS.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 32 to 38 deg. F.
Max. temperature in the last 24 hours: 33 to 38 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 60 to 70 mph
Maximum wind gust in the last 24 hours: 137 mph
New snowfall in the last 24 hours: Snow: 3 to 12 inches | Rain: 2.8 to 4.5 inches
Total snow depth: 96 to 136 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Thursday Thursday Night Friday
Weather: Cloudy. Rain through the day. Snow in the afternoon. Snow levels 8000 feet decreasing to below 7000 feet in the afternoon. Chance of precipitation is 100%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 95%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 100%.
Temperatures: 36 to 41 deg. F. 19 to 24 deg. F. 22 to 27 deg. F.
Mid Slope Winds: Southwest 25 to 35 mph with gusts to 45 mph. Southwest 30 to 40 mph with gusts to 70 mph. Southwest 25 to 35 mph decreasing to 15 to 30 mph in the afternoon. Gusts up to 45 mph.
Expected snowfall: 70% probability of 6 to 12 inches. 30% probability of 10 to 15 inches. | SWE = 1.20-1.70 inches. 80% probability of 10 to 15 inches. 20% probability of 12 to 20 inches. | SWE = 0.55-1.00 inch. 80% probability of 10 to 18 inches. 20% probability of 15 to 25 inches. | SWE = 0.60-1.10 inches.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Cloudy. Rain in the morning. Snow through the day. Snow levels 8000 feet decreasing to below 7000 feet in the afternoon. Chance of precipitation is 100%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 95%. Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 100%.
Temperatures: 33 to 39 deg. F. 17 to 22 deg. F. 18 to 23 deg. F.
Ridge Top Winds: Southwest 60 to 70 mph in the afternoon. Gusts up to 120 mph. Southwest 65 to 75 mph with gusts to 125 mph. Southwest 35 to 55 mph with gusts to 105 mph decreasing to 30 to 45 mph with gusts to 75 mph in the afternoon.
Expected snowfall: 70% probability of 12 to 18 inches. 30% probability of 15 to 30 inches. | SWE = 1.05-1.95 inches. 80% probability of 10 to 16 inches. 20% probability of 12 to 20 inches. | SWE = 0.65-1.10 inches. 80% probability of 12 to 18 inches. 20% probability of 18 to 26 inches. | SWE = 0.75-1.25 inches.
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