THIS AVALANCHE ADVISORY EXPIRED ON January 26, 2018 @ 6:55 am
Avalanche Advisory published on January 25, 2018 @ 6:55 am
Issued by Steve Reynaud - Tahoe National Forest

Considerable avalanche danger will exist today due to wind slab, storm slab, and deep slab avalanche problems.  Wind slabs will be likely in near and above treeline areas.  Storm slabs and deep slabs will be likely in near and below treeline areas.  Dangerous avalanche conditions exist.  Careful snowpack evaluation, 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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Winds slabs will be likely today in near and above treeline terrain on NW-N-NE-E-SE-S aspects.  Strong to gale force SW winds yesterday and overnight have built large wind slabs.  These wind slabs will continue to grow today as winds increase in speed from the W.  Natural and human triggered wind slab avalanches are expected.

Look for signs of active wind loading; blowing snow, cornice formation, and wind pillows.  Wind slabs could continue to be reactive even if wind speeds decrease.  Snow surface clues can help determine where wind slabs may have formed last night.

Avalanche Problem 2: Storm Slab
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Storm slab avalanches are likely today in below treeline and near treeline terrain on all aspects.  Buried surface hoar has been found in several locations around the forecast area.  This surface hoar has been found in open areas in near treeline and below treeline terrain where winds have not destroyed it.  Buried surface hoar is capable of being remotely triggered and can fail on lower angle slopes.  In addition, storm slabs could also fail on weaknesses 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.  These storm slabs will be in wind protected near and below treeline terrain.  Avoid areas that show signs of unstable snow and avoid avalanche runout zones.

Avalanche Problem 3: Deep Slab
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The persistent weak layer that has affected our forecast area for many weeks is now buried 2-4'+ deep below the snow surface.  This deep persistent slab avalanche problem has been found in isolated areas on NW-N-NE aspects in near and below treeline terrain.  This weak layer continues to show unstable snowpack test results.  With the additional storm load last night, concern exists that this weak layer could fail.  A deep slab avalanche would have large consequences.   

Deep slab avalanches are unpredictable and hard to collect additional information on.  Tracks on a slope will not be an indicator of stability.  Look for collapsing, cracking, or whumpfing sounds.  Although, no signs of instability may be present.  Remote triggering is possible, along with failure mid to low slope.  A storm snow related avalanche could have the potential to step down into these weak old snow layers.  Avoid steep avalanche terrain and runout zones where this problem may exist. 

recent observations

* Wind slab avalanches reported on Wildflower Ridge (Donner Summit area) and Stevens Peak (Carson Peak area).

* Wind slab development with unstable test results on Red Lake Peak (Carson Pass area) and Rubicon Peak (West Shore area).

* Buried surface hoar has been observed on Andesite Peak and Wildflower Ridge (Donner Summit area), Silver Peak (Pole Creek area), Lincoln Ridge (Yuba Pass area), and Squaw Ridge (Carson Pass area).

* Snowpack tests targeting the deep persistent weak layer yesterday showed unstable results on Wildflower Ridge (Donner Summit area) and Stevens Peak (Carson Pass area).

Weather and CURRENT CONDITIONS
weather summary

The main cold front has left our area early this morning and has deposited 8 to 14'' of new snow throughout the forecast region.  Shower bands have set up behind the cold front.  If these bands persist in a certain area, an additional 4 to 6'' of snow could be possible in localized areas mainly east of the crest.  Another wave moves into our area this afternoon and evening.  Depending on how much lake enhancement occurs, potentially heavy additional snow is possible.  Snow showers should taper off by early Friday morning.

Drier conditions with warmer temperatures will return for the weekend.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 12 to 22 deg. F.
Max. temperature in the last 24 hours: 36 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 30 to 60 mph
Maximum wind gust in the last 24 hours: 103 mph
New snowfall in the last 24 hours: 8 to 12 inches
Total snow depth: 34 to 58 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. Scattered snow showers in the morning then widespread snow showers in the afternoon. Cloudy. Widespread showers in the evening then scattered snow showers after midnight. Mostly cloudy. Slight chance of snow showers in the morning.
Temperatures: 22 to 27 deg. F. 12 to 17 deg. F. 28 to 34 deg. F.
Wind Direction: SW SW SW
Wind Speed: 15 to 20mph with gusts to 40mph. 15 to 20mph with gusts to 35mph. 10 to 15mph in the morning becoming light. Gusts to 30mph.
Expected snowfall: Likely 1 to 5 in. | Possible 5 to 10 in. Likely 1 to 3 in. | Possible 3 to 5 in. 0 in.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy. Scattered snow showers in the morning then widespread snow showers in the afternoon. Cloudy. Widespread showers in the evening then scattered snow showers after midnight. Mostly cloudy.
Temperatures: 16 to 22 deg. F. 8 to 13 deg. F. 25 to 30 deg. F.
Wind Direction: W SW SW
Wind Speed: 20 to 35mph with gusts to 50mph. 20 to 30mph with gusts to 50mph decreasing after midnight. 15 to 25mph with gusts to 40mph.
Expected snowfall: Likely 3 to 6 in. | Possible 6 to 10 in. Likely 2 to 5 in. | Possible 5 to 8 in. 0 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