THIS AVALANCHE ADVISORY EXPIRED ON January 5, 2014 @ 6:53 am
Avalanche Advisory published on January 4, 2014 @ 6:53 am
Issued by Brandon Schwartz - Tahoe National Forest

Pockets of MODERATE avalanche danger remain near treeline and below treeline on NW-N-NE aspects on slopes steeper than 32 degrees with consistent snow cover. This is due to lingering persistent slabs. In these areas, the possibility of human triggered avalanches remains ongoing. For all other areas avalanche danger is either LOW or non-existent due to the lack of snow cover.

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

Variability in avalanche danger exists around the forecast area. Persistent slabs linger in some areas near treeline and below treeline on NW-N-NE aspects where the faceted Dec 7 persistent weak layer remains unstable. Field observations from the past 3+ weeks have shown the greatest amount of ongoing instability with little to no week to week improvement in the Carson Pass and Pole Creek/Deep Creek areas. Observations from the Yuba Pass, Mount Rose, Donner Summit, West Shore Tahoe, and Echo Summit areas have shown significantly less ongoing instability and in some cases stable conditions near treeline and below treeline on NW-N-NE aspects.

Triggering and going for a short ride in even a small avalanche at this time will almost certainly have significantly elevated consequences due to the almost guaranteed impact with rocks, logs, or trees due to the shallow snowpack. Becoming caught in the same size avalanche above a more typical deep Sierra snowpack could very well have minimal consequences.

recent observations

Spatial variability exists around the forecast area and there are significant snowpack stability differences on near treeline and below treeline NW-N-NE aspects from one area to another. The persistent weak instability on the Dec 7 facet layer has improved greatly in some areas and remains quite unstable in other areas. Recent observations from around the forecast area have shown this spacial variability. In the Carson Pass area on Dec 31, travel on near treeline and below treeline N-NE aspects in the area south of Red Lake produced cracking and collapsing of the snowpack. Some of the collapses occurred on the same slopes and areas previously collapsed by the same forecaster traveling through the area on Dec 12. Click here and watch the video showing very impressive collapse and propagation of the faceted Dec 7 persistent weak layer along a 2 meter (6.6ft) wide extended column test in this area. It is an excellent illustrator of the ongoing snowpack instability that has persisted for nearly a month in the Carson Pass, Pole Creek, and Deep Creek areas. Other recent observations from the Yuba Pass, Donner Summit, West Shore Tahoe, and Mount Rose areas have shown better overall snowpack stability with little current weakness and propagation along the Dec 7 facet layer.

Avalanche danger on SE-S-SW-W aspects has been almost entirely eliminated due to melt. Some snow cover exists on E aspects, but the Dec 7 facet layer has not been observed at any elevation on E aspects. The Dec 7 facet layer is also absent above treeline on NW-N-NE aspects. This is allowing for LOW avalanche danger in these areas. Near treeline and below treeline on NW-N-NE aspects, continued snowpack settlement has reduced the overall snowpack height and allowed rocks, logs, and stumps to show through the snowpack in places that were previously covered.

Weather and CURRENT CONDITIONS
weather summary

A dry cold front is passing through the region this morning. Maximum daytime air temperatures are forecast to drop 5 to 15 degrees today compared to yesterday. The most significant cooling is expected to occur north of Hwy 50. Ridgetop winds are shifting from west to northwest with the cold front passage this morning. Wind speeds will briefly go light as winds shift to the east behind the front and then increase to moderate in speed this afternoon. Sunny skies are expected through the weekend with light winds on Sunday.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 28 to 38 deg. F.
Max. temperature in the last 24 hours: 47 to 52 deg. F.
Average wind direction during the last 24 hours: West
Average wind speed during the last 24 hours: 20 mph
Maximum wind gust in the last 24 hours: 33 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: Sunny skies. Clear skies. Sunny skies.
Temperatures: 40 to 47 deg. F. 25 to 35 deg. F. 40 to 47 deg. F.
Wind Direction: North shifting to East in the afternoon. East Variable
Wind Speed: 5 to 15 mph. 5 to 15 mph. Light winds
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Sunny skies. Clear skies. Sunny skies.
Temperatures: 35 to 45 deg. F. 26 to 36 deg. F. 40 to 47 deg. F.
Wind Direction: Northwest shifting to East in the afternoon. East Variable
Wind Speed: 10 to 20 mph. Gusts up to 35 mph. 10 to 15 mph. Gusts up to 25 mph. Light winds
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.