THIS AVALANCHE ADVISORY EXPIRED ON January 2, 2014 @ 7:00 am
Avalanche Advisory published on December 31, 2013 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE avalanche danger still exists near and below treeline on NW-N-NE aspects on slopes steeper than 32 degrees where consistent snow cover exists due to lingering persistent slab instability.

Human triggered avalanches remain possible.

Brandon will update the advisory again in 2014 on Jan. 2 at 7:00 am.

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

In general if a NW-N-NE aspect has enough snow to recreate on, then human triggered persistent slab avalanches remain possible. Even though these kind of avalanches have become unlikely on some slopes, most sheltered near and below treeline areas with consistent snow cover still hold a slab sitting on top of a fragile weak layer waiting for the right trigger to break it loose. Areas where a shallower snowpack exists or trigger points like shallowly buried rocks represent the most likely places to trigger an avalanche. Trying to find these trigger points on a snow covered open slope would be quite difficult without x-ray vision.

The increase in variability and uncertainty associated with the persistent slabs makes accessing snowpack stability difficult. Even though most observations may point to a stable slope, it only takes finding that one hidden trigger point to start a failure that could take down the whole slope. Using the terrain to avoid the avalanche hazard by recreating on lower angle slopes that remain disconnected from steeper and deeper terrain represents a fun and safe plan when conditions like this exist.

Between the lingering persistent slabs and the shallow snow cover over rocks, logs, and other objects, significant hazards exist in the backcountry.

recent observations

Yesterday on Mt. Judah (more info, snowpit, photo) observations did not reveal any signs of instability. The Dec. 7th facets still remain in the lower half of the snowpack, but tests indicated that a fracture traveling through this persistent weak layer has become unlikely. No human-triggered collapsing or cracking occurred in this area either. Unfortunately, significant melting had also taken place here exposing many more rocks and patches of bare ground on all aspects. Finding a place with consistent and continuous snow cover large enough to make more than 5 turns has become challenging in this area.

Yesterday's observation from Mt. Judah represents one of the few showing no signs of instability since Dec. 7th. Since that time 25 out of 30 observations have shown unstable results. Since Dec. 25, 4 out of 6 observations have shown unstable results. Data does seem to indicate that the snowpack has begun to gain some strength, but this process is very slow. Overall observations show a snowpack whose stability or instability varies greatly from slope to slope or even across an individual slope, and that stability or instability has become difficult to access.

Weather and CURRENT CONDITIONS
weather summary

High pressure remains over the west coast and will continue to keep the weather dry and warm for the foreseeable future. Some systems passing by the region to the north may send a few clouds and light to moderate winds into the area over the next few days. Other than that expect partly cloudy to mostly sunny skies with daytime highs in the mid to upper 40's above 7000 ft.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 32 to 40 deg. F.
Max. temperature in the last 24 hours: 45 to 49 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 15 to 20 mph
Maximum wind gust in the last 24 hours: 36 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 7 to 13 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy Clear with a few clouds developing overnight Partly cloudy to mostly sunny
Temperatures: 43 to 50 deg. F. 30 to 35 deg. F. 42 to 50 deg. F.
Wind Direction: Southwest Variable Variable
Wind Speed: 10 to 15 mph Light Light
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy Clear with a few clouds developing overnight Partly cloudy to mostly sunny
Temperatures: 40 to 45 deg. F. 25 to 35 deg. F. 41 to 48 deg. F.
Wind Direction: Southwest Northwest Variable
Wind Speed: 15 to 25 mph with gusts to 35 mph 10 to 15 mph with gusts to 25 mph becoming light after midnight 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.