THIS AVALANCHE ADVISORY EXPIRED ON February 28, 2014 @ 6:43 am
Avalanche Advisory published on February 27, 2014 @ 6:43 am
Issued by Brandon Schwartz - Tahoe National Forest

Near and above treeline, avalanche danger is MODERATE with pockets of CONSIDERABLE danger on NW-N-NE-E-SE aspects on slopes 35 degrees and steeper. Below treeline, avalanche danger is MODERATE on all aspects that held previous snow cover on slopes 35 degrees and steeper.

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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Wind slabs are expected as the most widespread avalanche problem today. Wind loaded areas near treeline and above treeline on NW-N-NE-E-SE aspects will hold the largest slabs which may be up to 2 to 3 feet thick. Snowpack failure is expected to occur at or above the old/new snow interface. Natural avalanche activity may have occured last night. Isolated natural avalanches remain possible this morning. Human triggered avalanches will remain possible to likely throughout the day today.

Avalanche Problem 2: Storm Slab
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Unstable storm slabs may exist near treeline and below treeline on all aspects that held snow cover prior to last night's snowfall. N aspects below treeline that have dry near surface facets at or within an inch or so of the old/new snow interface will have a higher likelihood of instability. Snowpack failure is expected to occur just below, at, or above the old/new snow interface with slab thickness expected at around 10 to 18 inches. Human triggered avalanches will remain possible below treeline throughout the day today. 

recent observations

In the vast majority of locations a strong and stable snowpack capped by melt-freeze crust existed prior to last night's snowfall. In most areas, crust will exist today at the old/new snow interface. A few exceptions have been noted on north aspects where weaker faceted snow exists at the old/new snow interface.

Observations made yesterday near Grouse Rocks (Ward Canyon area) revealed foggy conditions and above freezing air temperatures that allowed for moisture to wet near surface facets that existed below treeline on N aspects in this area. At 8,300', only the top 0.5 inch of near surface facets were wet with an additional 2 to 3 inches of dry weak faceted snow below. At 7,500' more wet snow existed with wet near surface facets up to 2 inches deep on N aspects.

Other recent observations on Round Top Peak (Carson Pass area) and on Powderhouse Peak (Luther Pass area) noted that northerly aspect bed surfaces from slab avalanche activity Feb 8-9 hold several layers of weak faceted snow. These areas are higher in elevation than the observed areas yesterday in Ward Canyon. These areas may have escaped snow surface wetting, allowing for a more significant weak layer to have been buried at the old/new snow interface.

Weather and CURRENT CONDITIONS
weather summary

The period of highest intensity snowfall associated with the current weather system has past with snowfall activity tapering down to snow showers this morning. New snow amounts of 9 to 14 inches have accumulated above 7,500' across the forecast area. Spillover to the eastern portion of the forecast area was better than expected. Ridgetop winds shifted from south to southwest yesterday afternoon and are strong in speed this morning. Moderate to strong southwest winds are forecast to continue today, tonight, and tomorrow. Additional snowfall amounts of 2 to 5 inches are expected to accumulate today. Maximum daytime air temperatures are forecast to reach the upper 20s to mid 30s today for areas above 7,000'. A second storm system will pass through the region tomorrow bringing another round of significant snowfall.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 22 to 29 deg. F.
Max. temperature in the last 24 hours: 34 to 42 deg. F.
Average wind direction during the last 24 hours: South Southwest
Average wind speed during the last 24 hours: 32 mph
Maximum wind gust in the last 24 hours: 86 mph
New snowfall in the last 24 hours: 11 to 14 inches
Total snow depth: 45 to 54 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Thursday Thursday Night Friday
Weather: Cloudy skies, becoming mostly cloudy. Snow in the morning, snow showers in the afternoon. Partly cloudy skies becoming mostly cloudy. Isolated snow showers in the evening. Scattered snow showers after midnight. Cloudy skies with snow.
Temperatures: 28 to 35 deg. F. 21 to 28 deg. F. 31 to 38 deg. F.
Wind Direction: Southwest South Southeast
Wind Speed: 15 to 25 mph with gusts to 35 mph. 15 to 20 mph with gusts to 35 mph. 15 to 25 mph with gusts to 35 mph.
Expected snowfall: 2 to 5 in. Trace in. 6 to 9 in.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Cloudy skies, becoming mostly cloudy. Snow in the morning, snow showers in the afternoon. Partly cloudy skies becoming mostly cloudy. Isolated snow showers in the evening. Scattered snow showers after midnight. Cloudy skies with snow.
Temperatures: 29 to 35 deg. F. 20 to 27 deg. F. 28 to 35 deg. F.
Wind Direction: Southwest Southwest shifting to south after midnight. South
Wind Speed: 50 to 55 mph decreasing to 40 to 45 mph in the afternoon. Gusts up to 80 mph. 35 to 40 mph with gusts to 70 mph, shifting and decreasing to 25 to 30 mph with gusts to 45 mph after midnight. 25 to 35 mph with gusts to 55 mph.
Expected snowfall: 3 to 5 in. Trace in. 6 to 10 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.