THIS AVALANCHE ADVISORY EXPIRED ON February 3, 2014 @ 6:59 am
Avalanche Advisory published on February 2, 2014 @ 6:59 am
Issued by Brandon Schwartz - Tahoe National Forest

Avalanche danger is LOW for all elevations and aspects. Keep in mind that the definition of LOW danger states that human triggered avalanches are unlikely on a regional scale but could still occur in isolated areas or extreme terrain.

1. Low

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Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Near Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Wind Slab
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Winds have shifted from east to southwest over the past 24 hours. Areas of blowing snow were visible above treeline yesterday despite the forecast for light winds. Recently formed wind slabs could exist on a variety of aspects above treeline and along sparsely treed ridgelines.

Avalanche Problem 2: Persistent Slab
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In areas above 9,500' to 9,800', rain did not percolate full depth through the faceted old snow layers on near treeline and below treeline NW-N-NE aspects. In these upper elevation areas, problematic facet layers were not destroyed by the rain that fell in areas of lower elevation. Human triggered persistent slab avalanches are not impossible on slopes that represent the highest elevation near treeline and below treeline terrain within the forecast area. In these areas, weak layers of well developed facets and depth hoar exist below the overlying slab of recent new snow.

recent observations

Observations made yesterday near Red Lake and Elephant's Back (Carson Pass area) and near Grouse Rocks (Ward Canyon area) gave continued indications that the snowpack is continuing to gain strength. In these areas, bonding of recent new snow to the rain crust at the top of the old snow layers remained strong. This is despite a very strong temperature gradient within the snowpack that indicates the potential for a new near crust facet layer to form on top of the rain crust. Surface hoar crystals up to 1 cm in size were widespread in these areas as well.

Things to keep an eye on: 1) Formation of a new layer of near crust facets in between the rain crust and the overlying slab of recent new snow. 2) Burial and preservation of large areas of surface hoar by snow showers this week.

If the near crust facet layer forms, this metamorphosis of snow crystals on the ground could create a new weak layer within the snowpack. If this were to occur, snowpack stability could begin to increase rather than continue to decrease. Slopes that were stable yesterday could become unstable over the next several days. With a forecast for below average air temperatures, surface hoar might persist. If sizable areas of surface hoar are buried a problematic weak layer could be in place for later snow storms, potentially at the end of this week.

Weather and CURRENT CONDITIONS
weather summary

An offshore weather system moving down the coast of California will bring cloud cover and isolated snow showers to the forecast area today. Any areas of intense snow showers will likely hold off until the evening hours with a trace to 2 inches of accumulation possible. Areas south of Lake Tahoe have the best chance of receiving the upper end of forecast snowfall amounts. Otherwise, the trend of below average air temperatures will continue this week. Maximum daytime air temperatures are forecast to reach the upper teens to upper 20s today for areas above 7,000'. Moderate speed southwest winds filled in yesterday afternoon and are forecast to continue today and tomorrow. Another chance of snow showers is in the forecast for tomorrow afternoon.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 11 to 21 deg. F.
Max. temperature in the last 24 hours: 25 to 33 deg. F.
Average wind direction during the last 24 hours: East shifting to Southwest
Average wind speed during the last 24 hours: 23 mph
Maximum wind gust in the last 24 hours: 37 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 15 to 33 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy skies, becoming cloudy. Isloated snow showers in the afternoon. Mostly cloudy skies. Isolated snow showers in the evening. Partly cloudy skies, becoming mostly cloudy. A slight chance of snow showers in the afternoon.
Temperatures: 24 to 30 deg. F. 15 to 21 deg. F. 25 to 31 deg. F.
Wind Direction: Southwest Southwest West
Wind Speed: Light winds Light winds Light winds increasing to 10 to 15 mph in the afternoon.
Expected snowfall: 0 to trace in. Trace to 2 in. 0 to trace in.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy skies, becoming cloudy. Isloated snow showers in the afternoon. Mostly cloudy skies. Isolated snow showers in the evening. Partly cloudy skies, becoming mostly cloudy. A slight chance of snow showers in the afternoon.
Temperatures: 18 to 25 deg. F. 10 to 16 deg. F. 19 to 26 deg. F.
Wind Direction: Southwest South to southwest West
Wind Speed: 10 to 15 mph with gusts to 25 mph in the morning, becoming light. Light winds increasing to 10 to 15 mph with gusts to 25 mph after midnight. 10 to 15 mph with gusts to 25 mph, increasing to 20 to 25 mph with gusts to 35 mph in the afternoon.
Expected snowfall: 0 to trace in. Trace to 2 in. 0 to trace 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.