THIS AVALANCHE ADVISORY EXPIRED ON January 27, 2018 @ 6:45 am
Avalanche Advisory published on January 26, 2018 @ 6:45 am
Issued by Brandon Schwartz - Tahoe National Forest

MODERATE avalanche danger exists above and below treeline due to a combination of wind slab and persistent slab avalanche problems. Significant uncertainly exists regarding the persistent slabs due to a change in weak layer of concern, isolated distribution, and a lack of data. Do not let an absence of signs of instability below treeline create a sense of security that discounts the possibility of an isolated avalanche problem.

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.

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: Wind Slab
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Wind slabs remain a concern, especially with a second round of snowfall and SW wind yesterday afternoon through last night. Near and above treeline areas on NW-N-NE-E-SE aspects is the most likely terrain for wind slabs to exist. With the lull in snowfall yesterday morning, new wind slabs may have built on top of existing wind slabs. Avalanche size to D2 is possible (large enough to bury or injure a person).

Look for clues such as cornice formations, wind pillows, and stiff surface snow to help identify and avoid areas of potentially unstable wind slab.

Avalanche Problem 2: Persistent Slab
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Don't get fatigued on messaging with persistent slabs. The nature of this avalanche problem has changed. The deeply buried facet layer that has been the focus of this avalanche problem for the past several weeks is not the main focus today. Different weak layers buried less than one foot below the old snow/storm snow interface are now the focus of the problem. Isolated areas of near crust facets, especially in the Carson Pass area and buried surface hoar that had been observed in several locations around the forecast area pre storm are now the weak layers of concern. Data is lacking creating increased uncertainly.

The location of this problem is near treeline and below treeline terrain on NW-N-NE aspects. Many of the below treeline open areas for this problem do not look like avalanche paths so remain focused on slope angle. The weak layer distribution is isolated so it will be easy to go all day seeing no signs of instability below treeline. Avalanche size D2 is expected with the isolated possibility to size D3.

Keep a vigilant watch for snow surface cracking and/or snowpack collapse with a possible whumpfing sound in wind protected areas. These are signs of an unstable snowpack related to this avalanche problem.

recent observations

* Natural wind slab avalanches were reported yesterday from The Far East Ridge of Tamarack Peak (Mount Rose area) and from the south end of Andesite Ridge (Donner Summit area). In both cases, cornice fall may have been the trigger. Debris were covered with new snow indicating that the avalanches had occurred either Wednesday night or very early Thursday morning.

* Additional signs of instability were difficult to find yesterday while traveling on Tamarack Peak and on Andesite Ridge.

* No areas of buried surface hoar were examined yesterday so avalanche activity is unknown. Significant uncertainty remains regarding stability in any areas were buried surface hoar exists.

Weather and CURRENT CONDITIONS
weather summary

Snowfall has mostly come to an end over the region with a few lingering snow showers possible this morning over the northern portion of the forecast area. The second wave of snowfall yesterday afternoon and last night deposited an additional 2 to 9 inches around the forecast area. This brought storm totals to 14 to 24 inches above 7,000'. Ridgetop winds remain out of the SW this morning and are decreasing in speed. Some lingering cloud cover is expected today. A weather system will pass by to the north of the forecast area on Saturday, keeping wind direction from the SW. High pressure will begin to build over the region on Sunday.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 14 to 19 deg. F.
Max. temperature in the last 24 hours: 15 to 25 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 32 mph
Maximum wind gust in the last 24 hours: 56 mph
New snowfall in the last 24 hours: 4 to 9 inches
Total snow depth: 33 to 63 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 to mostly cloudy skies. Isolated snow showers possible in the morning. Mostly cloudy skies. Mostly cloudy skies with a slight chance of snow showers in the morning.
Temperatures: 28 to 34 deg. F. 21 to 26 deg. F. 40 to 45 deg. F.
Wind Direction: SW SW SW
Wind Speed: Light winds. Gusts up to 25 mph in the morning. Light winds becoming 10 to 15 mph with gusts to 30 mph after midnight. 10 to 15 mph with gusts to 35 mph in the morning, becoming light.
Expected snowfall: 0 in. 0 in. 0 to trace in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Partly to mostly cloudy skies. Isolated snow showers possible in the morning. Mostly cloudy skies. Mostly cloudy skies with a slight chance of snow showers in the morning.
Temperatures: 25 to 30 deg. F. 20 to 25 deg. F. 36 to 41 deg. F.
Wind Direction: SW SW W
Wind Speed: 10 to 15 mph with gusts to 35 mph. 15 to 25 mph. Gusts to 35 mph increasing to 50 mph after midnight. 20 to 30 mph. Gusts to 55 mph decreasing to 45 mph in the afternoon.
Expected snowfall: 0 in. 0 in. 0 to trace 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