THIS AVALANCHE ADVISORY EXPIRED ON January 19, 2018 @ 6:55 am
Avalanche Advisory published on January 18, 2018 @ 6:55 am
Issued by Steve Reynaud - Tahoe National Forest

Low avalanche danger will continue to exist throughout most of the day.  As the approaching winter storm impacts our region late this afternoon/evening, avalanche danger will begin to increase.  By this evening, considerable avalanche danger will exist.  Wind slab, storm slab, and persistent slab avalanche problems will become likely during the evening and overnight hours.  Natural avalanche activity is likely and dangerous avalanche conditions will exist.

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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Strong to gale force SW winds along with rapid loading of new snow will quickly start building wind slabs late this afternoon.  Wind slabs will continue to build throughout the evening and overnight with natural wind slab avalanches likely.  These wind slabs are expected to be on NW-N-NE-E aspects in near and above treeline terrain.

Look for blowing snow, new cornice formation, and wind pillows as clues to where wind slabs are forming.  Avoid steep wind loaded terrain.

Avalanche Problem 2: Storm Slab
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Storm slabs will be likely on all aspects in near and below treeline terrain.  These storm slabs could have weakness within the new storm snow or at the old snow/new snow interface. 

Look for cracking around skis, shooting cracks, or any signs of cohesion within the new storm snow.  Avoid areas that show signs of unstable snow.

Avalanche Problem 3: Persistent Slab
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Persistent slabs will become possible on NW-N-NE aspects in isolated areas in near treeline and below treeline terrain.  This weak layer remains active in isolated areas throughout the forecast region.  Concern exists that this layer could fail with a large load of new snow.  Any avalanche due to this persistent slab avalanche problem would have elevated consequences due to increased slab size involved. 

Look for collapsing, cracking, and whumpfing sounds.  Remote triggering is possible, along with failure mid to low slope.  Avoid steep avalanche terrain and runout zones where this problem may exist. 

recent observations

* Unstable test results reported in near and below treeline terrain on the buried facet layer over the last week.  Other locations are showing this layer and the overall snowpack gaining strength including Slab Cliffs (Mt. Rose area) and Waterhouse Peak (Luthur Pass area) yesterday.

* 1 natural triggered persistent slab avalanche on Jan. 11 reported.  No human triggered avalanches reported on this weak layer.

* NW-N-NE aspects above 8,000' in the Mt. Rose area and along the Sierra Crest north of Emerald Bay hold the best coverage at 2 to 4+ feet. Overall less snow cover exists south of Emerald Bay. Areas of decent coverage exist above 8,300' on NW-N-NE aspects in the Carson Pass area.  Coverage decreases dramatically on all other aspects.

Weather and CURRENT CONDITIONS
weather summary

A fast moving winter storm is set to impact our region from late this afternoon into Friday morning.  Wind gusts are forecasted to be over 100mph over the Sierra ridges and peaks.  Up to 10'' of snow is possible along the Sierra Crest with 4 to 7'' expected at lake level.  Localized amounts could reach up to 18'' in some areas.  Snowfall rates are forecasted to be up to 2''/hour for the bulk of the storm during the evening through early morning hours.  Additional snowfall is possible through Friday.  Another storm is expected Sunday into Monday.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 32 to 40 deg. F.
Max. temperature in the last 24 hours: 49 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: 85 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 21 to 38 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy. Chance of rain and snow in the afternoon. Cloudy. Rain in the evening and snow through the night. Cloudy. Snow showers likely.
Temperatures: 43 to 49 deg. F. 23 to 28 deg. F. 25 to 30 deg. F.
Wind Direction: SW SW SW
Wind Speed: South winds 25 to 35mph shifting to the SW 30 to 45mph in the afternoon. Gusts up to 70mph. 25 to 40mph. Gusts to 70mph decreasing to 55mph after midnight. 15 to 25mph. Gusts up to 50mph decreasing to 30mph in the afternoon.
Expected snowfall: Up to 2 in. 6 to 12 in. 1 to 4 in.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy. Chance of rain and snow in the afternoon. Cloudy. Snow. Cloudy. Snow showers likely.
Temperatures: 38 to 44 deg. F. 20 to 25 deg. F. 22 to 27 deg. F.
Wind Direction: SW SW SW
Wind Speed: 45 to 65mph with gusts to 105mph. 40 to 60mph. Gusts to 110mph decreasing to 95mph after midnight. 20 to 35mph with gusts to 65mph decreasing to 15 to 25mph with gusts to 45mph in the afternoon.
Expected snowfall: Up to 2 in. 7 to 12 in. 1 to 4 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