THIS AVALANCHE ADVISORY EXPIRED ON February 8, 2015 @ 6:49 am
Avalanche Advisory published on February 7, 2015 @ 6:49 am
Issued by Brandon Schwartz - Tahoe National Forest

Avalanche danger has risen to CONSIDERABLE for areas above 8,000' near and above treeline on NW-N-NE-E-SE aspects on slopes 35 degrees and steeper. For all other areas, avalanche danger is MODERATE on slopes 35 degrees and steeper. Human triggered avalanches are expected today. Don't let the desire for powder negatively affect sound decision making. Specifically choosing slopes based on slope angle will be the difference between "getting lucky" and "getting it done" in the backcountry today.

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.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Above 8,000', newly formed wind slabs exist on NW-N-NE-E-SE aspects and potentially in isolated areas on other aspects as well. Gale force winds throughout the period of snowfall will have created wind slabs in just about any lee areas both above and below treeline. Rising snow levels during the event will have deposited increasingly high density snow on top of (relatively) lower density snow creating an opportunity for slab over non-persistent weak layer formation. Slab depths of 2 to 4+ feet are possible today in heavily wind loaded areas. Ongoing human triggering of these wind slabs is expected today with avalanche size easily large enough to bury and/or injure a person.

Avalanche Problem 2: Storm Slab
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In areas of protection from ongoing SW winds, storm slabs are possible above 8,000' on all aspects where new snow was deposited on top of an old snow bed surface. Rising snow levels will again have created the potential for slab over non-persistent weak layer formation. Human triggered avalanches will remain possible today in wind protected areas both near and below treeline with slabs depths of 6 inches to 1.5 feet. Some of these storm slabs may present with wet slab characteristics.

recent observations

Recent observations from around the forecast area including those made yesterday on Tamarack Peak (Mount Rose area) indicated that the existing snowpack was in good condition to handle the new loading from rain and snow received over the past 18 hours. Rain and melt freeze crusts that exist at or just below the old snow surface are strong and supportable. Softer layers of rounding facets and rounded snow grains below these crusts have given no indication of holding the proper characteristics to support propagation upon collapse. Avalanche activity from last night and ongoing instability today are expected to occur at or above the old/new snow interface.

Weather and CURRENT CONDITIONS
weather summary

The atmospheric river that brought high intensity rain and snow to the region yesterday afternoon and last night has moved off to the south of the forecast area this morning. Snow levels started as low as 5,500' before rising to around 8,500' for much of the precipitation event. New snow amounts between 8,000' and 9,000' range from 6 to 14 inches in most areas with up to 20 inches above 9,000' in isolated areas. Ridgetop winds remain gale force this morning out of the southwest with a maximum gust of 142 mph recorded over Ward Peak last night. Ridgetop winds are forecast to decrease from gale force to strong in speed with ridgetop gusts to 75 mph continuing today. Air temperatures at 8,000' to 9,000' are in the low to mid 30s this morning. Maximum daytime air temperatures are expected to reach the low 30s to low 40s today for areas above 7,000'. Cloudy skies with light rain and snow are expected to continue into this afternoon with additional new snow amounts of up to 3 inches above 7,000'. A second storm system will impact the forecast area tomorrow with snow levels expected to start out around 8,000' with around 4 inches of new snow possible tomorrow over the upper elevations.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 32 to 36 deg. F.
Max. temperature in the last 24 hours: 39 to 43 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 66 mph
Maximum wind gust in the last 24 hours: 142 mph
New snowfall in the last 24 hours: 6 to 14 inches
Total snow depth: 28 to 45 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 skies with snow and rain showers. Cloudy skies with rain and snow likely. Cloudy skies with rain likely.
Temperatures: 35 to 42 deg. F. 29 to 36 deg. F. 39 to 46 deg. F.
Wind Direction: SW SW SW
Wind Speed: 25 to 30 mph with gusts to 50 mph, decreasing to 15 to 20 mph with gusts to 35 mph in the afternoon. 20 to 25 mph with gusts to 35 mph. 25 to 30 mph with gusts to 45 mph.
Expected snowfall: Up to 2 in. Up to 1 in. 0 in.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy skies with snow showers. Cloudy skies with snow and rain likely. Cloudy skies with snow and rain likely.
Temperatures: 31 to 38 deg. F. 28 to 35 deg. F. 35 to 42 deg. F.
Wind Direction: SW SW SW to S
Wind Speed: 55 to 60 mph with gusts to 90 mph, decreasing to 45 to 50 mph with gusts to 75 mph in the afternoon. 45 to 50 mph with gusts to 75 mph, decreasing to 30 to 35 mph with gusts to 55 mph ater midnight. 50 to 55 mph with gusts to 80 mph, decreasing to 35 to 40 mph with gusts to 60 mph in the afternoon.
Expected snowfall: 1 to 3 in. Up to 1 in. 1 to 4 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.