THIS AVALANCHE ADVISORY EXPIRED ON January 10, 2017 @ 6:55 am
Avalanche Advisory published on January 9, 2017 @ 6:55 am
Issued by Andy Anderson - Tahoe National Forest

Dangerous avalanche conditions still exist and large, deep, destructive human-triggered avalanches remain likely due to deep slabs and wind slabs. CONSIDERABLE avalanche danger exists at all elevations. This danger rating is when the most avalanche fatalities occur. Carefully evaluate the snowpack and terrain and use this information to create safe and conservative travel plans. Avoid areas where avalanche problems may exist. The avalanche danger will rise to HIGH again tonight as more snow and wind impact the forecast area.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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New snow and continued gale-force winds today will create wind slabs on top of the refreezing snowpack. These wind slabs will form in typical leeward areas in near and above treeline terrain and could extend onto open slopes in below treeline terrain as well due to the strength of the winds. Human triggered wind slab avalanches will be likely today and natural wind slab avalanches will be possible. As snowfall intensity increases tonight natural and human triggered wind slabs will become likely to very likely again. Wind slabs could exist on wind loaded NW-N-NE-E-SE aspects at all elevations and could step down to the deep slabs mentioned below. 

Use clues like blowing snow, cornices, drifts, wind-created surface textures and other evidence of wind transport to identify where wind slabs exist and avoid them. 

Avalanche Problem 2: Deep Slab
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Human triggered deep slab avalanches that fail on the facets near the 12/15 rain crust will be likely today and natural deep slabs may remain possible on W-NW-N-NE-E aspects at all elevations. This problem will linger until the snowpack has had time to refreeze and gain some strength. This refreezing process does not happen overnight and could take a few days for the cold temperatures to permeate through the snowpack. Any of these avalanches that do occur would be large, very deep, and destructive. They could also run much farther than expected and involve snow that is still wet from yesterday.

Deep slabs are unpredictable and traditional observations do not provide reliable data about them. Sometimes the first sign of instability is a deep slab avalanche even on a tree-covered slope or a slope with tracks on it. Remote triggering with large propagation into any connected terrain remains possible. Avoiding any terrain where this problem might exist represents the wisest choice for today. Deep slabs can occur on less steep slopes and any slopes steeper than 30 degrees are suspect. 

recent observations

Yesterday observations on Carson Pass revealed widespread wet deep slab avalanches, deep wet wind slab avalanches, loose wet avalanches on N-NE-E-SE aspects. Many of the slab avalanches had crowns in the 4 to 7 ft. range and looked to have failed naturally due to rain loading the snowpack and causing the facets near the 12/15 rain crust to break. Some avalanches broke higher in the snowpack. These avalanches looked to have occurred during the night on Saturday night or on Sunday morning. The avalanches occurred in below treeline, near treeline, and above treeline terrain and on small slopes tucked into tree-covered areas as well as on large open slopes. 

Weather and CURRENT CONDITIONS
weather summary

3 to 6.4 inches of rain has fallen on the forecast area up to 9000 to 9300 ft. in the last 24 hours. At the highest elevations, some heavy wet snow accumulated and some sensors in the 8000-9000 ft. range reported 4 to 6 inches of new snow with up to 12 inches in the last 24 hours. Hurricane force winds that averaged in the 65 to 85 mph range with gusts as high as 180 mph were recorded during the last 24 hours. Snow levels started to drop last night and made it to around 7000 ft. by 4 am. By 6 am snow had started falling at Lake level. Snow levels should continue to fall to around 5000 today. Snow should continue today with convective showers this morning and another strong storm moving into the area this afternoon. The forecast calls for another 5 to 10 inches of new snow today. Snowfall should start to increase this afternoon as the next storm arrives. Tonight and tomorrow could see another 12 to 24 inches of snow each period. The forecast calls for this storm to remain strong through Wed. morning. Temperatures should remain cold through tonight keeping snow levels around 5000 ft. north of Hwy 50 and 5000-6000 ft. south of Hwy 50. Tomorrow could bring some warmer temperatures pushing snow level back up into the 6000-7000 ft. range before more cold air moves into the area Tuesday night. Gale force southwest winds should continue through this storm.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 24 to 33 deg. F.
Max. temperature in the last 24 hours: 35 to 40 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 65 to 85 mph
Maximum wind gust in the last 24 hours: 180 mph
New snowfall in the last 24 hours: Snow: 4 to 12 inches | Rain 3 to 6.4 inches
Total snow depth: Along the Sierra Crest: 41 to 61 inches | In the Mt. Rose area: 93 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Monday Monday Night Tuesday
Weather: Snow Snow Snow
Temperatures: 29 to 34 deg. F. 22 to 27 deg. F. 30 to 35 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 25 to 35 mph with gusts to 50 mph 25 to 35 mph with gusts to 60 mph 25 to 40 mph with gusts to 65 mph
Expected snowfall: 5 to 10 in. 12 to 20 in. 10 to 20 in.
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Snow Snow Snow
Temperatures: 26 to 32 deg. F. 19 to 24 deg. F. 25 to 31 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 35 to 55 mph with gusts to 100 mph 35 to 55 mph with gusts to 105 mph increasing to 115 mph after midnight 40 to 60 mph with gusts to 120 mph
Expected snowfall: 5 to 10 in. 12 to 24 in. 12 to 24 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