THIS AVALANCHE ADVISORY EXPIRED ON February 6, 2017 @ 6:40 am
Avalanche Advisory published on February 5, 2017 @ 6:40 am
Issued by Steve Reynaud - Tahoe National Forest

Moderate avalanche danger exists in near treeline and above treeline terrain due to a continuing wind slab avalanche problem.  Low avalanche danger exists in below treeline terrain.  Human triggered wind slab avalanches remain possible for today.  Avalanche danger will rise tonight and through Monday as the first in a series of storms impact our region this week.

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Wind slabs will continue to be a problem on NW-N-NE-E-SE aspects in near treeline and above treeline terrain.  Wind slabs will continue to grow as SW winds increase to strong to gale force this afternoon.  Human triggered wind slab avalanches remain possible today.  Existing wind slabs have grown throughout this storm cycle and could be well over 3 to 4' deep.  Avalanches associated with these deeper wind slabs would have large consequences.

Look for blowing snow, cornice formation, wind pillows, and snow surface scouring as clues to where wind slab development is occurring or has occurred.  Avoid steep wind loaded terrain.  

recent observations

Observations were received from Silver Peak (Pole Creek area), Andesite Peak (Donner Summit area), and Round Valley (Donner Summit area).  All areas showed continued settlement of the recent storm snow with around 2 feet of new settled snow since the storm began on Wednesday.  Rain levels were reported up to 7000' in the morning hours with generally heavy and dense surface snow.  On Silver Peak and in Round Valley,  ECT's were propagating on wind slab failures up to 1' deep in the snowpack.  Active wind loading was occurring at all locations throughout the day.

Weather and CURRENT CONDITIONS
weather summary

An active and wet week is in store for the area with strong winds, heavy mountain snow, and heavy rainfall.  A break in storm activity is expected today.  SW winds will increase to gale force this afternoon as the first storm for the week approaches our region tonight.  Late Sunday night through Monday night could bring multiple feet of snow above 7000'.  Uncertainty still exists with this storm on exact snow levels and how much snow will be expected for Lake level.  On Tuesday, warm subtropical moisture moves into the area with rising snow levels and heavy rainfall which could continue through Friday.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 27 to 32 deg. F.
Max. temperature in the last 24 hours: 32 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: No data available. mph
Maximum wind gust in the last 24 hours: No data available. mph
New snowfall in the last 24 hours: Trace to 2 inches
Total snow depth: 107 to 141 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. Cloudy. Snow. Cloudy. Snow.
Temperatures: 38 to 43 deg. F. 26 to 31 deg. F. 28 to 32 deg. F.
Wind Direction: SW SW SW
Wind Speed: 15 to 25mph. Gusts up to 50mph increasing to 60mph in the afternoon. 20 to 35mph with gusts to 70. 30 to 45mph with gusts to 70mph.
Expected snowfall: 0 in. 4 to 8 in. 6 to 10 in.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy. Mostly cloudy. Snow likely in the evening then snow after midnight. Cloudy. Snow.
Temperatures: 33 to 39 deg. F. 24 to 27 deg. F. 26 to 30 deg. F.
Wind Direction: SW SW shifting to S SW
Wind Speed: 30 to 45mph with gust to 70mph increasing to 35 to 55mph with gusts to 90mph in the afternoon. 45 to 60mph with gusts to 105mph becoming south and increasing to 60 to 75 with gusts to 130mph. 60 to 80mph. Gusts up to 140mph decreasing to 130mph in the afternoon.
Expected snowfall: 0 in. 4 to 10 in. 8 to 12 in.
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