THIS AVALANCHE ADVISORY EXPIRED ON December 16, 2015 @ 6:58 am
Avalanche Advisory published on December 15, 2015 @ 6:58 am
Issued by Steve Reynaud - Tahoe National Forest

Pockets of Moderate avalanche danger exist on all aspects above treeline and on NW-N-NE aspects near treeline and below treeline.  Low danger exists for all other areas.  Avalanche problems for today consist of wind slabs and persistent slabs.  In isolated areas, human triggered avalanches are possible today.  Evaluate snow and terrain carefully, identify features of concern.

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: Persistent Slab
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Persistent slab avalanche problems are still a lingering concern in isolated terrain for today.  The surface hoar that was buried on 12/13 and caused human and natural triggered avalanches is still being found on N-NE aspects near treeline and below treeline in wind protected but open terrain.  Yesterday the surface hoar that was found was mainly not reactive to snowpack tests and hand pits and appeared to have collapsed from the weight of the new snow above.  There have been no reports of additional avalanches associated with this weak layer since Sunday but there still could be pockets were this layer is still reactive. 

The 12/10 and 12/13 rain crust both formed early in the last 2 storm cycles as warm storms approached then quickly turned to cold snow.  Developing near crust facets on both these layers could pose a persistent weak layer for now and into the future.  These problems have been seen in the Carson Pass/Ebbetts Pass/Bear Valley area on NW-N-NE aspects 8000' to 9000'.  In the Carson Pass area yesterday, snowpack tests were showing that both these layers were reactive.  The 12/13 layer is down about 1' and the 12/10 layer is down around 2.5' from surface.  In other areas this weak layer has not been seen.

Avalanche Problem 2: Wind Slab
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Ongoing NE winds in the moderate to strong range will continue to scour the above treeline N-NE-E aspects and move snow onto the SE-S-SW-W-NW aspects today  Wind slabs will continue to develop on these aspects with pockets of wind slabs found in complex terrain on all aspects above treeline.  Recent below average cold temperatures will slow the bonding process of these wind slabs and have them linger through today.  Look for blowing snow, snow surface scouring, cornice formation, and well defined wind pillows for clues as to where wind slabs may occur.

recent observations

Recent observations throughout the forecast area have shown that the 12/13 buried surface hoar layer is limited to specific areas and limited in reactivity.  Most of this surface hoar was thought to be destroyed by wind, sun and rain before it could be buried by new snow.  At Blue Lakes (Carson Pass Area) and at Powderhouse Peak (Luther Pass Area) the buried surface hoar layer was not found.  At Hidden Peak (West Shore) it was found in protected open areas but not reactive and thought to have collapsed under the weight of the new snow.

Moderate to strong NE winds were redistributing existing snow and creating small sensitive wind slabs that were reactive to a skiers' weight on all aspects above treeline.  This was observed on Hidden Peak (West Shore) and blowing snow was seen near and above treeline in the Carson Pass and Mt. Rose areas.

Developing near crust facets have been observed at the 12/10 and 12/13 rain crusts.  These facets are becoming reactive to snowpack tests and have mostly been limited to the southern half of the forecast region (Carson Pass, Ebbetts Pass/Bear Valley 8000-9000'.)  No other signs of instability have been associated with these layers.

 

 

Weather and CURRENT CONDITIONS
weather summary

High pressure with a cold northerly flow expected to stay with us through Wednesday with well below average cold temperatures.  NE ridgetop winds in the moderate to strong range are forecasted for today and tomorrow.  Sunny skies expected throughout today with highs in the teens to low 20's above 7000'.  Valley inversions will remain strong with poor mixing through Wednesday.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 7 deg. F.
Max. temperature in the last 24 hours: 18 deg. F.
Average wind direction during the last 24 hours: NE
Average wind speed during the last 24 hours: 20 to 30 mph
Maximum wind gust in the last 24 hours: 56 mph
New snowfall in the last 24 hours: Trace inches
Total snow depth: 32 to 40 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny Clear then becoming partly cloudy. Partly cloudy.
Temperatures: 16 to 23 deg. F. 10 to 18 deg. F. 26 to 31 deg. F.
Wind Direction: NE NE N
Wind Speed: 10 to 20mph with gusts to 35mph. 10 to 15mph with gusts to 30mph 10 to 15mph
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny Clear then becoming partly cloudy. Partly cloudy.
Temperatures: 15 to 22 deg. F. 14 to 18 deg. F. 24 to 31 deg. F.
Wind Direction: NE NE NW
Wind Speed: 20 to 35mph with gusts to 55mph 20 to 30mph with gusts to 55mph 15 to 25mph with gusts to 40mph.
Expected snowfall: 0 in. 0 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.