THIS AVALANCHE ADVISORY EXPIRED ON January 20, 2017 @ 6:50 am
Avalanche Advisory published on January 19, 2017 @ 6:50 am
Issued by Steve Reynaud - Tahoe National Forest

Considerable avalanche danger exists at all elevations due to wind slab and storm slab avalanche problems.  Dangerous avalanche conditions exist.  Natural triggered avalanches are possible and human triggered avalanches are likely.  Cautious route finding and conservative decision making are essential today.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Wind slabs started to develop quickly yesterday by mid day as new snow and gale force SW winds moved into the forecast area.  These wind slabs have grown in size overnight and will continue to increase in size through the morning.  Winds slabs are expected on NW-N-NE-E-SE aspects in near treeline and above treeline terrain.

Look for blowing snow, cornice formation, wind pillows, and snow surface clues as to where wind slabs exist.  Avoid recently wind loaded terrain.

Avalanche Problem 2: Storm Slab
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Storm slabs will be possible on all aspects in near treeline and below treeline terrain today.  Many areas throughout the forecast area have received 12'' of new snow with more snow forecasted this morning.  A rise in temperature during the storm last night before cooling back off may have contributed to an upside down storm snow structure.  In some areas, this new storm snow may have fallen on existing near surface facets or surface hoar.

Signs of storm snow instabilities could be snow surface cracking, snow collapsing, and whumpfing.  Avoid slopes steeper than 30 degrees in areas where signs of unstable storm slabs are present.

recent observations

Observations were made and received yesterday from Castle Peak (Donner Summit area) and Elephants Hump (Carson Pass area).  Wind slabs were forming and reactive by late morning on Castle Peak.  Strong to gale force winds were moving snow along exposed areas as the storm came in earlier than forecasted.  On Elephants Hump, the old snow surface consisted of a variety of crusts and wet snow.  Both areas showed relatively good bonding with the new snow to the existing snow surface.

Weather and CURRENT CONDITIONS
weather summary

A winter weather advisory is in effect through 10am this morning.  We have received 8 to 15'' of new snow throughout the forecast area with gale force winds overnight.  Winds have decreased this morning but are still in the strong to gale force range over the Sierra Crest and will continue throughout the morning.  We will have a brief break this afternoon before the next storm approaches late tonight into early Friday morning.  Another winter weather advisory begins at 4am Friday morning and continues until 10am Saturday.  A larger storm is expected for Sunday and Monday. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 19 to 25 deg. F.
Max. temperature in the last 24 hours: 37 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 40 to 60 mph
Maximum wind gust in the last 24 hours: 112 mph
New snowfall in the last 24 hours: 10 to 15 inches
Total snow depth: 86 to 118 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. Snow in the morning then chance of snow showers in the afternoon. Cloudy. Chance of snow showers in the evening then snow showers likely after midnight. Cloudy. Snow.
Temperatures: 25 to 30 deg. F. 17 to 22 deg. F. 26 to 31 deg. F.
Wind Direction: SW SW S
Wind Speed: 15 to 25mph. Gusts up to 60mph decreasing to 35mph in the afternoon. 15 to 20mph. Gusts up to 30mph increasing to 40mph after midnight. 15 to 25mph with gusts to 55mph.
Expected snowfall: Up to 2 in. Up to 2 in. 4 to 8 in.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Cloudy. Snow in the morning then snow showers likely in the afternoon. Cloudy. Chance of snow showers in the evening then snow showers likely after midnight. Cloudy. Snow.
Temperatures: 22 to 28 deg. F. 15 to 20 deg. F. 23 to 29 deg. F.
Wind Direction: SW SW SW
Wind Speed: 30 to 40 with gusts to 85mph decreasing to 15 to 25mph with gust to 50mph in the afternoon. 20 to 30mph. Gusts up to 50mph increasing to 65mph after midnight. 30 to 45mph. Gusts up to 85mph increasing to 100mph in the afternoon.
Expected snowfall: 1 to 2 in. 1 to 2 in. 4 to 8 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