THIS AVALANCHE ADVISORY EXPIRED ON January 2, 2018 @ 6:52 am
Avalanche Advisory published on December 31, 2017 @ 6:52 am
Issued by Steve Reynaud - Tahoe National Forest

Moderate avalanche danger continues at all elevations due to a persistent slab avalanche problem as our existing snowpack continues to weaken over time.  Human triggered avalanches are possible throughout the forecast region in isolated areas.  Identify and avoid areas of concern.  This avalanche advisory will be updated by 7am on Tuesday, January 2.

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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    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Persistent slab avalanches are possible on NW-N-NE aspects at all elevations.  The current dry spell through much of December has allowed our existing snowpack to facet and lose strength over time creating a layer of loose sugary snow.  This layer of weak faceted snow has recently become reactive to the weight of a person, causing cracking, whumpfing, and unstable snowpack tests results.  While faceted snow is widespread on many NW-N-NE aspects, having a slab on top is not.  In isolated areas near and above treeline, hard wind slabs are on top of this faceted weak layer.  In isolated areas below treeline, soft slabs are on top of this faceted weak layer.  This will be an ongoing problem as this weak layer continues to facet and lose strength. 

Look for cracking around skis, whumpfing sounds, and any signs that a slab may exist above weak faceted snow.  Hand pits may help to see if there is a cohesive surface slab on top of loose faceted snow.  Use safe travel protocols when traveling in and around avalanche terrain.  The consequences of being caught in an avalanche are elevated, even a small one, with our low snowpack conditions.

recent observations

* Signs of persistent slab instability on NW-N-NE aspects including snow surface cracking, whumpfing, and/or unstable snowpit test results have occurred during the past several days in the Carson Pass, Desolation Wilderness, West Shore Tahoe,  Deep Creek, Pole Creek, and Donner Summit areas. In all cases, failure occurred on faceted snow beneath either a hard or soft slab.

* Near surface facets without an overlying slab are fairly widespread on northerly aspects in wind protected, below treeline areas.

* Snow surface conditions range from wind scoured snow and firm ice near and above treeline to lingering areas of soft unconsolidated snow on sheltered northerly aspects below treeline.

* Northerly aspects above 8000 ft 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, but decent coverage exists above 8,500 ft. on northerly aspects in the Carson Pass area.  Coverage becomes patchy on other aspects with large areas of bare ground on many southerly aspects at all elevations.

Weather and CURRENT CONDITIONS
weather summary

Continued high pressure with light winds and dry conditions will wrap up 2017.  Mid to high level clouds will continue with above average temperatures into Tuesday.  Unsettled weather could bring rain and high elevation snow to the forecast area by midweek.

 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 34 to 41 deg. F.
Max. temperature in the last 24 hours: 48 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 15 to 25 mph
Maximum wind gust in the last 24 hours: 39 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 16 to 32 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy. Mostly cloudy. Mostly cloudy then becoming partly cloudy.
Temperatures: 47 to 52 deg. F. 30 to 36 deg. F. 48 to 53 deg. F.
Wind Direction: SW SW
Wind Speed: Up to 10mph. Up to 10mph. Light winds
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy. Mostly cloudy. Mostly cloudy then becoming partly cloudy.
Temperatures: 42 to 48 deg. F. 31 to 37 deg. F. 44 to 50 deg. F.
Wind Direction: SW SW SW
Wind Speed: 10 to 20mph with gusts to 30mph. 10 to 15mph with gusts to 30mph. 10 to 15mph in the morning becoming light.
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.

For a recorded version of the Avalanche Advisory call (530) 587-3558 x258