THIS AVALANCHE ADVISORY EXPIRED ON December 28, 2013 @ 6:41 am
Avalanche Advisory published on December 27, 2013 @ 6:41 am
Issued by Brandon Schwartz - Tahoe National Forest

Near treeline and below treeline avalanche danger remains MODERATE on NW-N-NE aspects on slopes steeper than 32 degrees due to lingering persistent slab instability.

Human triggered avalanches remain possible. 

1. Low

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Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

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
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Persistent slab instability remains ongoing near treeline and below treeline on NW-N-NE aspects. The faceted Dec 7 persistent weak layer is slowly gaining strength, but not enough to make much difference in terms of reducing avalanche danger. Between the lingering persistent slabs and the shallow snow cover over rocks, logs, and other objects, significant hazard exists in the backcountry.

recent observations

Observations made yesterday on Red Lake Peak (Carson Pass area) matched well with other recent observations from around the forecast area. Persistent slab instability lingers near treeline and below treeline on NW-N-NE aspects. The Dec 7 facet layer is buried under a fairly well consolidated slab and remains reactive in snowpit tests. Once this weak layer collapses, it has the necessary characteristics to allow a fracture to propagate through the snowpack.

Spacial variability is increasing around the forecast area in regards to stability improvements of the Dec 7 faceted weak layer. The amount of force required to trigger weak layer collapse and the ability for the weak layer to propagate are becoming more variable from one location to another. In some spots, strength increases in the Dec 7 persistent weak layer are highly evident while in other areas the strength gains have been much more modest. Either way, the data still indicates that human triggered avalanches are possible in many locations around the forecast area.

Weather and CURRENT CONDITIONS
weather summary

High pressure continues to dominate the weather forecast. A weak frontal system will pass through the forecast area this weekend. This system will bring some increasing cloud cover this afternoon as well as an increase in southwest winds. No precipitation is expected. Maximum daytime air temperatures are expected to reach well into the 40s today for areas above 7,000'. Around 5 degreees of cooling is expected for tomorrow.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 30 to 42 deg. F.
Max. temperature in the last 24 hours: 46 to 53 deg. F.
Average wind direction during the last 24 hours: E shifting to SW
Average wind speed during the last 24 hours: 20 mph
Maximum wind gust in the last 24 hours: 35 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 8 to 16 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Sunny skies, becoming partly cloudy. Mostly cloudy skies, becoming partly cloudy. Sunny skies.
Temperatures: 44 to 51 deg. F. 30 to 40 deg. F. 38 to 42 deg. F.
Wind Direction: SW SW W
Wind Speed: 15 to 20 mph with gusts to 30 mph. 15 to 20 mph with gusts to 30 mph. 10 to 15 mph with gusts to 25 mph.
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Sunny skies, becoming partly cloudy. Mostly cloudy skies, becoming partly cloudy. Sunny skies.
Temperatures: 40 to 50 deg. F. 27 to 37 deg. F. 35 to 45 deg. F.
Wind Direction: SW SW W
Wind Speed: 15 to 20 mph with gusts to 30 mph, increasing to 25 to 30 mph with gusts to 40 mph in the afternoon. 20 to 30 mph. Gusts to 45 mph, decreasing to 35 mph after midnight. 15 to 25 mph with gusts to 40 mph.
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.