THIS AVALANCHE FORECAST EXPIRED ON February 21, 2017 @ 6:55 am
Avalanche Forecast published on February 20, 2017 @ 6:55 am
Issued by Steve Reynaud - Tahoe National Forest

High Avalanche Danger will exist at all elevations due to the strong atmospheric river storm impacting our area.  Wind slab, storm slab, and loose wet avalanche problems will be very likely at all elevations.  Natural and human triggered avalanches are expected.  Travel in avalanche terrain is not recommended.  An avalanche warning has been issued until 7am Tuesday morning. 

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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Gale force SW winds will impact the forecast area throughout the day with large amounts of new snow possible at higher elevations.  Wind slabs are expected to be very likely and could be natural or human triggered.  These wind slabs will form above the rain level, which could vary throughout the day, but should be near 7000-7500'.  Most wind slabs will form on NW-N-NE-E-SE aspects in near and above treeline terrain but could also form on other aspects and below treeline.  Large cornice formation is expected.  Travel in or around avalanche terrain is not recommended.  Avoid avalanche run out zones.

Avalanche Problem 2: Storm Slab
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Storm slabs will be very likely today due to heavy new snow and varying temperatures throughout the storm.  These storm slabs will exist on all aspects in near treeline and below treeline terrain.  An upside down storm snow structure will be possible as snow levels fluctuate throughout the storm.  These storm slabs could be dry or wet depending on elevation and varying snow levels.

Travel in or around avalanche terrain is not recommended.  Avoid avalanche run out zones.

Avalanche Problem 3: Loose Wet
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Loose wet avalanches are very likely on all aspects in below treeline and near treeline terrain.  Most loose wet activity will occur below or near the snow level where heavy rain is falling on new or existing snow.  Natural loose wet activity is expected and could be anything from roller balls to much larger avalanches with severe consequences.  Travel in avalanche terrain is not recommended.  Avoid avalanche terrain and avalanche run out zones. 

recent observations
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Observations were made and received from Mt. Tallac (Desolation Wilderness area), Angora and Talking Mountains (Echo Summit area), Andesite Peak (Donner Summit area), Carpenter Peak (Independence Lake area), Stevens Peak (Carson Pass area), and Shirley Canyon (Squaw Valley area).  Human triggered avalanches were reported on Angora Peak, Talking Mountain, and Stevens Peak.  Most of these avalanches were newly forming wind slabs but some were storm slabs that formed lower down in more protected terrain.  All areas had strong SW winds with blowing snow and wind slab development in near treeline and above treeline terrain.  Wet snow existed below 7500' with some minor loose wet activity observed.    

Weather and CURRENT CONDITIONS
weather summary

A strong atmospheric river storm has begun to impact our area overnight and will continue through Tuesday.  4 to 7'' of snow has fallen overnight above 7500'.  Peak wind gusts have been over 100mph early this morning.  3 to 6'' of rain is forecasted throughout the Greater Tahoe Basin with up to 2 to 5' of snow at the higher elevations by the end of Tuesday.  Snow levels are forecasted at 7000-7500', but are expected to vary throughout the storm.  Extreme winds with gusts up to 150mph are possible over Sierra passes and ridges.  Colder air should bring down snow levels during the day on Tuesday as the storm continues.  Unsettled and stormy weather continues into Wednesday with further cooling temperatures.  

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 28 to 33 deg. F.
Max. temperature: 34 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 50 to 70 mph
Maximum ridgetop wind gust: 124 mph
New snowfall: 4 to 7 inches
Total snow depth: 124 to 145 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Monday Monday Night Tuesday
Weather: Cloudy. Rain and snow. Cloudy. Rain and snow. Cloudy. Snow.
Temperatures: 37 to 42 deg. F. 28 to 33 deg. F. 30 to 35 deg. F.
Mid Slope Winds: SW SW SW
Wind Speed: 20 to 30mph with gusts to 65mph increasing to 25 to 40mph with gusts to 75mph in the afternoon. 30 to 50mph with gusts to 85mph. 25 to 40mph. Gusts to 75mph decreasing to 65mph in the afternoon.
Expected snowfall: 8 to 18 8 to 16 3 to 8
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Cloudy. Heavy snow. Cloudy. Heavy snow. Cloudy. Snow.
Temperatures: 32 to 37 deg. F. 25 to 30 deg. F. 26 to 32 deg. F.
Ridge Top Winds: SW SW SW
Wind Speed: 40 to 60mph increasing to 50 to 65mph in the afternoon. Wind gusts up to 130mph. 45 to 65mph with gusts to 155mph. 35 to 55mph. Gusts to 130mph decreasing to 115mph in the afternoon.
Expected snowfall: 12 to 24 10 to 20 4 to 9
Disclaimer

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.

For a recorded version of the Avalanche Advisory call (530) 587-3558 x258