THIS AVALANCHE ADVISORY EXPIRED ON February 19, 2017 @ 6:59 am
Avalanche Advisory published on February 18, 2017 @ 6:59 am
Issued by Andy Anderson - Tahoe National Forest

Some human-triggered wind slab avalanches may remain possible today. Near and above treeline MODERATE avalanche danger exists in wind-loaded areas. Evaluate the snowpack and terrain carefully to identify features where problematic wind slabs may exist and plan travel routes to avoid them.

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
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    Certain
    Very Likely
    Likely
    Possible
    Unlikely
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    Historic
    Very Large
    Large
    Small

Most wind slabs should remain relatively small and not extend very far away from the ridgelines, but some larger wind slabs may still exist in heavily wind-loaded areas. Human-triggerable wind slab avalanches may remain possible on wind-loaded slopes today. The snow that fell late yesterday afternoon and evening allowed the wind slabs to grow in size and distribution. While the forecast calls for the winds to remain light to moderate today in many areas, some wind transport and new loading may occur during periods of stronger winds and gusts today, especially along the Sierra Crest. Wind slabs could exist on almost any aspects in near and above treeline terrain due to the shifting wind directions over the last 36 hours. 

Identify where wind slabs may exist using clues like blowing snow, cornices, wind pillows, ripples across a slope, firm but hollow sounding snow, and other wind created textures. Use this information to plan a route that avoids the wind slabs and utilizes more sheltered terrain where better snow for recreation will exist.

recent observations

Yesterday observations on Andesite Peak, Fireplug, and the Talking Mountain ridge showed SE-E winds blowing snow and wind-loading leeward aspects. Most of the wind slabs formed by these winds remained small measuring only 3 to 6 inches in depth in the afternoon and did not extend very far downslope. On west aspects on Andesite Peak, some of these wind slabs reached 6 to 12 inches in depth in the most heavily wind-loaded areas. Ski cuts and kicks did trigger some cracking on Andesite and Fireplug. In the Talking Mountain area, snowboard cuts triggered small loose dry sluffs involving the top few inches of the new snow on steep test slopes. Snowpit data, hand pits, and other observations did not reveal significant signs of slab formation or instability in sheltered areas in all three locations. 

Weather and CURRENT CONDITIONS
weather summary

6 to 10 inches of new snow has fallen in the last 24 hours with most of the accumulation occurring yesterday afternoon and evening. Snowfall has diminished and the winds have shifted back to the southwest. Light to moderate southwest winds and scattered snow showers should continue through tomorrow without any significant accumulation. The winds should begin to increase tomorrow ahead of a large winter storm projected to impact the region Sunday night through Tuesday. Check in with the Reno NWS for more details.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 27 to 30 deg. F.
Max. temperature in the last 24 hours: 31 to 34 deg. F.
Average wind direction during the last 24 hours: E to SE shifting to SW
Average wind speed during the last 24 hours: 15 to 30 mph
Maximum wind gust in the last 24 hours: 75 mph
New snowfall in the last 24 hours: 6 to 10 inches
Total snow depth: 123 to 147 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy with a chance of snow. Scattered snow showers in the afternoon. Mostly cloudy with a chance of scattered snow showers Mostly cloudy with a chance of snow showers
Temperatures: 32 to 37 deg. F. 23 to 28 deg. F. 34 to 39 deg. F.
Wind Direction: Variable Southwest Southwest
Wind Speed: Light with gusts to 25 mph in the morning Light increasing to 10 to 15 mph with gusts to 30 mph after midnight 15 to 25 mph with gusts to 35 mph increasing to gusts to 50 mph in the afternoon.
Expected snowfall: up to 2 in. up to 1 in. up to 1 in.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy with a chance of snow. Scattered snow showers in the afternoon. Mostly cloudy with a chance of scattered snow showers Mostly cloudy with a chance of snow showers
Temperatures: 29 to 34 deg. F. 20 to 25 deg. F. 31 to 37 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 10 to 15 mph with gusts to 40 mph decreasing to gusts to 30 mph in the afternoon 15 to 20 mph with gusts to 30 mph increasing to gusts to 45 mph after midnight 20 to 35 mph with gusts to 65 mph increasing to gusts to 75 mph in the afternoon
Expected snowfall: up to 2 in. up to 1 in. up to 1 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