THIS AVALANCHE ADVISORY EXPIRED ON February 2, 2016 @ 6:58 am
Avalanche Advisory published on February 1, 2016 @ 6:58 am
Issued by Brandon Schwartz - Tahoe National Forest

MODERATE avalanche danger exists for all elevations and all aspects on slopes 35 degrees and steeper. New wind slabs formed near treeline and above treeline last night under gale force NE wind conditions. In wind protected areas below treeline, loose dry avalanche activity remains likely and small storm slabs remain possible. Don't let an absence of obvious clues of instability lull your party into a sense of security today.

 

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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A 4 to 6 hour period of gale force NE winds occurred last night and winds remain moderate in speed out of the NE this morning. This wind redistributed snow on the ground from yesterday. Areas of significant wind scouring and wind loading are expected today in near and above treeline areas. The majority of new wind slab formation is expected on SE-S-SW-W-NW aspects. In complex terrain a mix of scoured snow surfaces and pockets of wind slab will likely coexist on N-NE-E aspects. Areas of wind scouring, cornice formation, wind pillows, and snow surface texture will provide clues for identifying suspect slopes in near and above treeline terrain.

Areas of exposed rain crust on the snow surface are likely on windward aspects above treeline. The potential exists for long sliding falls with very difficult self arrest conditions.

Avalanche Problem 2: Loose Dry
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In wind protected areas below treeline loose dry avalanches will be likely in steep terrain. If choosing to venture onto slopes steeper than 35 degrees, evaluate the terrain for secondary hazards such as terrain traps, rocks, trees, and cliffs below that could greatly magnify the consequences of being pushed off line by a loose dry avalanche.

Avalanche Problem 3: Storm Slab
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New snow yesterday evening and last night produced one more opportunity for potential storm slabs to form in wind protected areas below treeline. Any subtle weak layers that exist within the upper portion of the recent new snow are likely to present as human triggered cracking in lower angle terrain. The depth of any storm slabs that might exist is expected to be less than 6 inches. Human triggered storm slab avalanche activity is unlikely to be large enough to bury a person unless occurring above a terrain trap such as a cliff or creek bed. This is where deeper burials can occur from small avalanches.

recent observations

A report was received yesterday of a skier triggered wind slab avalanche that occurred near the summit of Jakes Peak (West Shore Tahoe area). Details are few, but the avalanche was reported to have occurred on an E to NE aspect around 9,100' in near treeline terrain. The size of the avalanche was estimated at 100 feet wide with a 100 foot down slope run. No one was caught in the avalanche. Crown height was not reported.

Observations received yesterday from the north side of Carson Pass in above treeline terrain on an ENE aspect around 8,800' indicated that just over a foot of new snow had accumulated in the area late yesterday afternoon under calm wind conditions. This far exceeded the forecast expectations of 3 to 5 inches. Unstable snowpit test results with propagating characteristics were noted 2.5 to 3 feet below the snow surface within the recent storm snow.

Observations made yesterday on Castle Peak and Andesite Ridge (Donner Summit area) as well as on Tamarack Peak (Mount Rose area) saw little evidence of snowpack instability. Numerous ski cuts and intentional cornice collapses in these locations produced loose dry results on the slopes below with no signs of unstable wind slabs. On Tamarack Peak shallow storm slab instabilities were noted, but did not present a significant hazard to backcountry travelers during the mid day hours.

Weather and CURRENT CONDITIONS
weather summary

The storm system that brought heavy snowfall to portions of the forecast area yesterday is exiting the region. Last night, skies began to clear and a gale force wind event occurred. Average wind speeds of 30 to 60 mph with maximum gusts to 97 mph were recorded during the overnight hours. Air temperatures this morning are in the upper single digits to low teens for most locations above 7,000'. Maximum daytime air temperatures are forecast to reach the mid teens to mid 20s today for areas above 7,000'. A weak weather system will bring a chance of light snow showers to the forecast area tomorrow with no significant accumulation expected. As this weather system moves through the region, moderate speed ridgetop winds are expected to shift back to the west.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 8 to 11 deg. F.
Max. temperature in the last 24 hours: 21 to 27 deg. F.
Average wind direction during the last 24 hours: ENE
Average wind speed during the last 24 hours: 31 mph
Maximum wind gust in the last 24 hours: 97 mph
New snowfall in the last 24 hours: 4 to 10 inches
Total snow depth: 73 to 85 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy skies. A slight chance of snow early in the morning. Partly cloudy skies, becoming mostly cloudy. Mostly cloudy skies. A slight chance of snow showers.
Temperatures: 16 to 23 deg. F. 5 to 15 deg. F. 20 to 27 deg. F.
Wind Direction: NE N W
Wind Speed: 15 to 25 mph with gusts to 40 mph. Gusts decreasing to 30 mph in the afternoon. 15 to 25 mph with gusts to 35 mph. 15 to 20 mph with gusts to 30 mph.
Expected snowfall: 0 to trace in. 0 in. 0 to trace in.
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy skies. A slight chance of snow early in the morning. Partly cloudy skies, becoming mostly cloudy. Mostly cloudy skies. A slight chance of snow showers.
Temperatures: 13 to 20 deg. F. 4 to 11 deg. F. 16 to 23 deg. F.
Wind Direction: NE N W
Wind Speed: 25 to 35 mph with gusts to 55 mph. 25 to 35 mph with gusts to 55 mph. 20 to 30 mph with gusts to 45 mph.
Expected snowfall: 0 to trace 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.