THIS AVALANCHE ADVISORY EXPIRED ON January 12, 2014 @ 7:05 am
Avalanche Advisory published on January 11, 2014 @ 7:05 am
Issued by Andy Anderson - Tahoe National Forest

This morning the avalanche danger remains LOW for areas with consistent snow cover. As snow and wind impact the region some pockets of MODERATE avalanche danger may form on near and above treeline NW-N-NE-E-SE aspects steeper than 32 degrees. The most likley places where human triggered avalanches could become possible are the near treeline NW-N-NE aspects where the wind slabs could sit on top of persistent weak layers.

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.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

As new snow and wind impact the region today, wind slabs should start to form on wind-loaded and cross-loaded aspects. Due to the strength of the winds, these winds slabs could work their way into more sheltered areas like tree covered slopes or slopes farther downhill from the ridgelines. In these areas a weak snowpack with buried persistent weak layers already exists and adding even a small wind slab on top of it could be enough to make human triggered avalanches possible. The near treeline NW-N-NE aspects represent the best places where the most serious human triggered avalanches could become possible today. Other aspects and areas where presistent weak layers do not exist will only hold small wind slabs. If the snowfall amounts remain near the low end of the forecasted accumulation, the avalanches issues should remain small and isolated. If snowfall amounts reach the high end of the forecasted accumulation, the avalanche issues would be larger and more widespread. Either way, diligent observations to determine where wind slabs have formed and what kind of snowpack they formed above will help determine where fragile avalanche conditions may exist. Since the forecast calls for most of the snowfall to remain near the Sierra Crest, near the Sierra Crest is also where the most fragile avalanche conditions should form.

recent observations

Observations from Lincoln Ridge near Yuba Pass, Anderson Peak, and Scout Peak near Echo Summit all showed a snowpack with the Dec. 7th facet layer buried in the snowpack. On Lincoln Ridge and Anderson Peak a more consolidated layer of snow resided above this persistent weak layer with more soft unconsolidated weak snow at the surface. On Scout Peak the entire snowpack was weak and unconsolidated. In all three areas general observations and snowpit tests did not reveal signs of continued instability. These and other recent observations from around the forecast area indicate that in some areas the Dec. 7th facets have gained enough strength to support the small slabs above them. In other areas the small slab that used to exist above the persistent weak layer has simply lost its slab characteristics and become weak snow sitting on top of weak snow.

Weather and CURRENT CONDITIONS
weather summary

The SW winds started increasing last night due to a small fast moving low pressure system approaching the area. The forecast calls for this system to arrive today bringing even stronger SW winds, increased cloud cover, and some snow. Snowfall should begin sometime around mid-morning and continue into the afternoon. Most of the snow should fall along the Sierra Crest where the forecast calls for up to 5 inches. Areas east of the Crest and south of Carson Pass should receive much less snow. The storm should move east of the region overnight allowing the high pressure ridge to return tomorrow. For tomorrow expect clearing skies and strong NE winds as the high pressure re-establishes itself.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 30 to 38 deg. F.
Max. temperature in the last 24 hours: 40 to 49 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: Before midnight:5 to 10 mph | Since midnight: 30 to 40 mph
Maximum wind gust in the last 24 hours: 75 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.
Saturday Saturday Night Sunday
Weather: Mostly couldy with isolated snow showers in the morning. Snow becoming more widespread this afternoon. Mostly cloudy with some scattered snow showers in the evening. Snow tapering off overnight. Partly cloudy in the morning becoming sunny by the afternoon
Temperatures: 37 to 42 deg. F. 20 to 25 deg. F. 35 to 40 deg. F.
Wind Direction: Southwest Southwest Northwest shifing to the Northeast in the afternoon
Wind Speed: 30 to 45 mph with gusts to 75 mph 30 to 40 mph with gusts to 70 mph decreasing to 15 to 25 mph with gusts to 45 mph after midnight 10 to 15 mph increasing to 10 to 20 mph with gusts to 30 mph in the afternoon
Expected snowfall: 1 to 3 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Mostly couldy with isolated snow showers in the morning. Snow becoming more widespread this afternoon. Mostly cloudy with some scattered snow showers in the evening. Snow tapering off overnight. Partly cloudy in the morning becoming sunny by the afternoon
Temperatures: 31 to 38 deg. F. 20 to 25 deg. F. 28 to 33 deg. F.
Wind Direction: Southwest West shifting to the Northwest after midnight Northwest shifing to the North in the afternoon
Wind Speed: 45 to 60 mph with gusts to 90 mph increasing to 55 to 70 mph with gusts to 105 mph in the afternoon 50 to 60 mph with gusts to 95 mph decreasing to 30 to 45 mph with gusts to 80 mph after midnight 25 to 40 mph with gusts to 65 mph deceasing to 20 to 30 mph with gusts to 45 mph in the afternoon
Expected snowfall: 3 to 5 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.