THIS AVALANCHE ADVISORY EXPIRED ON January 13, 2018 @ 6:57 am
Avalanche Advisory published on January 12, 2018 @ 6:57 am
Issued by Brandon Schwartz - Tahoe National Forest

Avalanche danger is LOW for all elevations. On a regional scale, triggering an avalanche has become unlikely. Localized, isolated areas of instability may still exist where a human triggered persistent slab or wind slab avalanche could occur. Identify the specific avalanche problem that may exist in the desired area of travel and take appropriate steps to manage it.

1. Low

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

1. Low

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

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Persistent Slab
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Below treeline and near treeline terrain that is above 8,200' on NW-N-NE-E aspects is where any lingering persistent slab instability is most likely to exist. Faceted snow that is generally found 6 inches to 2 feet below the snow surface has become wet in some areas but remains dry to moist in other areas, especially around 9,000' and above. Open areas below treeline and near treeline with good protection from NE winds is where the facets had become weakest prior to the last round of storms. These same areas are the focus of lingering concern for this avalanche problem.

Keep in mind that triggering of a persistent slab avalanche could very well occur on the mid or lower portion of the slope, rather than near the top like a wind slab avalanche.

 

Avalanche Problem 2: Wind Slab
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Ridgetop winds out of the SW were strong in speed yesterday afternoon and last night. Small wind slabs may exist near and above treeline today on NW-N-NE-E-SE aspects. As winds shift to the NE tonight, redistribution of snow on the ground could create more small wind slab formation on SE-S-SW-W-NW aspects.

Look for clues such as recent cornice formation, wind pillows, and snow surface sculpting that identify areas of recently drifted snow and the potential location of this avalanche problem. Take appropriate steps to manage any areas of suspected wind slab.

recent observations

* Observations made yesterday specifically targeting faceted snow layers of the persistent slab avalanche problem on Red lake Peak (Carson Pass area) and on Rubicon Peak and Peak 9,269' (West Shore Tahoe area) indicated improving strength of the snowpack in the areas traveled.

*  Consistent unstable snowpit test results were observed Wednesday on Tamarack Peak (Mt. Rose area) on a buried layer of facets.  These observations were made on NW-N aspects in near treeline and below treeline terrain.

*  On Tuesday, a naturally triggered persistent slab avalanche occurred on Elephants Hump in the Carson Pass area.  Widespread signs of instability with collapsing, cracking, and whumpfing of the snowpack were also observed near and below treeline on N-NE-E aspects on Elephants Hump that day.

* NW-N-NE aspects above 8,000' in the Mt. Rose area and along the Sierra Crest north of Emerald Bay hold the best coverage at 2 to 4+ feet. Overall less snow cover exists south of Emerald Bay. Areas of decent coverage exist above 8,300' on NW-N-NE aspects in the Carson Pass area.  Coverage decreases dramatically on all other aspects.

Weather and CURRENT CONDITIONS
weather summary

High pressure currently building over the forecast area is expected to last through the weekend. As a result, expect decreasing cloud cover and warming air temperatures. A moderate speed NE wind event is forecast to occur tonight in response to the building high pressure. Air temperature inversion conditions are expected to form in the coming days. This will allow for the coldest overnight air temperatures this weekend to occur on the mountain valley floors while warmer air remains up on the peaks. The next series of storm systems are expected to impact the forecast area Tues through Fri.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 28 to 35 deg. F.
Max. temperature in the last 24 hours: 31 to 38 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 43 mph
Maximum wind gust in the last 24 hours: 75 mph
New snowfall in the last 24 hours: 0 to trace inches
Total snow depth: 22 to 38 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Partly cloudy skies, becoming sunny. Clear skies. Partly cloudy skies, becoming sunny.
Temperatures: 44 to 49 deg. F. 28 to 33 deg. F. 46 to 51 deg. F.
Wind Direction: W NE E
Wind Speed: Generally light winds with gusts to 40 mph decreasing to 25 mph in the afternoon. Generally light winds with gusts to 30 mph after midnight. Generally light winds with gusts to 30 mph in the morning.
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Partly cloudy skies, becoming sunny. Clear skies. Partly cloudy skies, becoming sunny.
Temperatures: 40 to 46 deg. F. 30 to 35 deg. F. 44 to 49 deg. F.
Wind Direction: W NE E
Wind Speed: 20 to 35 mph with gusts to 75 mph, decreasing to 15 to 25 mph with gusts to 50 mph in the afternoon. 10 to 15 mph with gusts to 35 mph. 10 to 15 mph with gusts to 35 mph 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