THIS AVALANCHE ADVISORY EXPIRED ON January 8, 2018 @ 6:58 am
Avalanche Advisory published on January 7, 2018 @ 6:58 am
Issued by Steve Reynaud - Tahoe National Forest

Moderate avalanche danger will exist today with wind slab and persistent slab avalanche problems.  Human triggered wind slab avalanches will be possible in near and above treeline terrain.  Persistent slab avalanches will continue to be possible at all elevations.  Areas of concern exist on specific terrain features, evaluate snow and terrain carefully.  Avalanche danger is expected to rise with the approaching storm on Monday.

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.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    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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Newly formed wind slabs yesterday could remain sensitive today on NW-N-NE-E-SE aspects in near and above treeline terrain above 8500'.  Increasing SW winds this afternoon could form new wind slabs and add weight to existing wind slabs.  In isolated areas, wind slabs may be on top of old near surface facets on NW-N-NE aspects.  Look for cornice formation, blowing snow, and signs of previous blowing snow, especially along ridgelines and wind exposed areas.

Avalanche Problem 2: Persistent Slab
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Yesterdays storm added significant rain and heavy snow to the layer of weak faceted snow that exists below the snow surface.  In some areas, these facets have gained strength from being wetted from the recent rain and heavy snow.  In high elevation areas and places that the facets are protected by an overlying slab, these facets remain dry and loose in many locations.  This faceted layer is still producing unstable snowpack test results along with cracking in isolated areas.  

Avoid steeper slopes in areas where snow surface cracking, whumpfing, and/or unstable snowpit test results are occurring.  Quick hand pits remain an effective tool for seeing if a slab over weak faceted snow exists.

advisory discussion

Up to 2'' of rain has fallen throughout the forecast area below 8500'.  The snow surface in these areas are expected to refreeze overnight and into this morning creating firm rain crusts on all aspects below 8500'.  Some softening is expected throughout the day as temperatures warm.  Roller balls could occur on E-SE-S-SW aspects depending on the amount of sun we receive today.  Larger loose wet avalanches are not expected today.  

recent observations

* Natural wind slab avalanche reported off of Elephants Back (Carson Pass area) yesterday.

* Natural D2 loose wet avalanche reported off of Twin Peaks (Ward Canyon area).

* Reports of wind slabs failing on old near surface facets in the Carson Pass area and Mt. Rose area.

* Where faceted snow exists under a slab, the facets continue to remain dry and reactive in snowpit tests.

* NW-N-NE aspects above 8,000' in the Mt. Rose area and along the Sierra Crest north of Emerald Bay hold the best snow coverage at 2 to 3+ feet. Overall less snow cover exists south of Emerald Bay. Areas of decent coverage exists above 8,500' on NW-N-NE aspects in the Carson Pass area.  Coverage decreases on all other aspects. Large areas of bare ground exist on the vast majority of southerly aspects at all elevations.

Weather and CURRENT CONDITIONS
weather summary

SW winds and cloud cover will increase today ahead of a significant winter storm expected for Monday through Tuesday.  High elevation snow and heavy rain is forecasted to start early Monday with high fluctuating snow levels before lowering into Tuesday.  A winter storm watch is in effect from Monday afternoon through Tuesday.  Dry and mild weather is expected late in the week and through the weekend.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 22 to 35 deg. F.
Max. temperature in the last 24 hours: 39 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 15 to 40 mph
Maximum wind gust in the last 24 hours: 73 mph
New snowfall in the last 24 hours: Trace inches
Total snow depth: 20 to 35 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy then becoming mostly cloudy. Mostly cloudy. Slight chance of rain and snow after midnight. Cloudy. Chance of rain and snow.
Temperatures: 43 to 48 deg. F. 32 to 37 deg. F. 41 to 46 deg. F.
Wind Direction: SW SW S
Wind Speed: Light winds. Gusts to 25mph in the afternoon. Light winds. Gusts up to 30 increasing to 40mph after midnight. 10 to 15mph. Gusts up to 35mph increasing to 50mph in the afternoon.
Expected snowfall: 0 in. 0 in. Likely 0 | Possible 1 to 2 in.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy. Mostly cloudy. Slight chance of snow after midnight. Cloudy. Chance of snow and rain.
Temperatures: 40 to 45 deg. F. 31 to 36 deg. F. 38 to 43 deg. F.
Wind Direction: SW SW S
Wind Speed: 15 to 20mph. Gusts to 30mph increasing to 40mph in the afternoon. 20 to 30mph. Gusts to 40mph increasing to 50mph after midnight. 20 to 30mph with gusts to 60mph increasing to 30 to 45mph with gusts to 80mph in the afternoon.
Expected snowfall: 0 in. 0 in. Likely 1 to 4 in. | Possible 4 to 7 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