THIS AVALANCHE ADVISORY EXPIRED ON February 25, 2017 @ 6:59 am
Avalanche Advisory published on February 24, 2017 @ 6:59 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE avalanche danger exists in near and above treeline terrain today with LOW danger in below treeline areas. Human triggered wind slab avalanches and loose snow sluffs will remain possible today. Carefully evaluate snowpack and terrain before committing to any slopes and use this information to avoid slopes where avalanche problems may exist.

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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While most wind slabs may have become more difficult to trigger, some human-triggerable wind slab avalanches may remain possible in near and above treeline terrain today. These could include larger wind slabs left over from the storm that linger on NW-N-NE-E-SE-S aspects as well as newer wind slabs formed by NW and NE winds in the last 36 hours. These newer wind slabs should remain smaller and exist near ridgelines on E-SE-S-SW-W aspects. The most fragile wind slabs will exist in the places most exposed to wind-loading and in terrain like gullies, couloirs, unsupported slopes above cliffs, and other steep, complex, and wind-loaded terrain.

Use clues such as blowing snow, cornice formations, and wind pillows to help identify recently wind-loaded slopes where unstable wind slabs may exist. Then use this information to plan a backcountry travel route that avoids the potentially unstable wind slabs and utilizes more sheltered terrain where better snow for recreation will exist.

Avalanche Problem 2: Loose Dry
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A cold, partly clear night means that the surface snow may have become less cohesive. Some loose snow sluffs could still remain possible on steep sheltered slopes. Most of these would occur where the coldest and least cohesive snow exists on NW-N-NE aspects

recent observations

Yesterday a small human-triggered wind slab avalanche occurred on a SE aspect on Angora Peak. Several small loose snow sluffs occurred on steep slopes in the Job/Freel area, on Tallac, in the Cinder Cone area (east of highway 89), and on Angora Peak as well. In these areas as well as on Tamarack Peak and on Donner Summit, a "right-side-up" snowpack that went from soft snow at the top to more dense consolidated snow below existed in sheltered locations. In wind exposed areas in these places, large cornices existed above slopes and some wind slabs did remain. Tests and observations targeting these wind slabs in the Job/Freel area, on Tamarack, and on Tallac did not find lingering wind slab instability on wind-loaded test slopes. Snow surfaces ranged from wind-scoured to firm wind-packed snow to soft wind affected snow in exposed areas and soft unconsolidated snow in sheltered areas. 

Weather and CURRENT CONDITIONS
weather summary

The forecast calls for partly sunny skies this morning with a layer of high clouds developing by this afternoon as a small low pressure approaches the region. Temperatures should remain cold with daytime highs in the 20's above 7000 ft. today and tomorrow. The southwest winds have returned and should continue to increase through tomorrow morning in response to the low pressure. Snow showers could arrive over the region late tonight or early tomorrow morning and continue through the day tomorrow. Snow accumulation should remain limited with only up to 2 inches expected tomorrow. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: -1 to 6 deg. F.
Max. temperature in the last 24 hours: 20 to 28 deg. F.
Average wind direction during the last 24 hours: NE to NW to SW
Average wind speed during the last 24 hours: 10 to 20 mph
Maximum wind gust in the last 24 hours: 35 mph
New snowfall in the last 24 hours: 0 to 1 inches
Total snow depth: 140 to 190 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 becoming mostly cloudy Partly cloudy becoming mostly cloudy with a 10% chance of isolated snow showers after midnight Mostly cloudy with a 45% chance of snow
Temperatures: 24 to 29 deg. F. 12 to 18 deg. F. 22 to 27 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: Light in the morning then increasing to 10 to 15 mph in the afternoon 10 to 15 mph with gusts to 35 mph 10 to 15 mph with gusts to 30 mph in the morning decreasing in the afternoon
Expected snowfall: 0 in. trace to 0 in. up to 2 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Partly cloudy becoming mostly cloudy Partly cloudy becoming mostly cloudy with a 10% chance of isolated snow showers after midnight Mostly cloudy with a 45% chance of snow
Temperatures: 20 to 26 deg. F. 11 to 16 deg. F. 17 to 22 deg. F.
Wind Direction: Southwest Southwest Southwest shifting to northwest in the afternoon
Wind Speed: 15 to 20 mph with gusts to 25 mph increasing to 40 mph in the afternoon 20 to 30 mph with gusts to 55 mph increasing to gusts to 65 mph after midnight 15 to 25 mph with gusts to 60 mph decreasing to 10 to 15 mph with gusts to 30 mph in the afternoon
Expected snowfall: 0 in. trace to 0 in. up to 2 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