THIS AVALANCHE ADVISORY EXPIRED ON April 15, 2013 @ 6:39 am
Avalanche Advisory published on April 14, 2013 @ 6:39 am
Issued by Brandon Schwartz - Tahoe National Forest

Early this morning, avalanche danger is LOW for all elevations and aspects. As the day progresses, areas of MODERATE danger will form on all aspects at all elevations on slopes 37 degrees and steeper in response to daytime warming. Small human triggered loose wet avalanches will become possible.

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.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Loose Wet
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    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

A decent snow surface refreeze is expected to have occurred last night due to air temperatures near or below freezing and radiational cooling of the upper snowpack mostly uninhibited by cloud cover. As daytime warming progresses, the snow surface will transition from frozen and supportable to melt phase with developing wet snow instability. Human triggered loose wet avalanches will become possible from late morning onward, especially during the afternoon and evening hours. Most areas of instability will exist on E-SE-S-SW-W aspects, spreading to include areas on NW-N-NE aspects later in the day. Above treeline areas with exposure to wind will experience convective cooling of the snow surface and slower melt rates than wind sheltered areas near treeline and below treeline. With many previous melt-freeze cycles and previous rain events having already occurred this winter and spring, free water drainage from the snowpack is well established. This is expected to keep loose wet avalanche activity limited to human triggered avalanches that are relatively small in size.

recent observations

Observations made yesterday on Castle Peak (Donner Summit area) indicated that a decent snow surface refreeze occurred in this area Friday night. In above treeline areas, moderate to strong southwest winds provided convective cooling of the snow surface which greatly slowed the rate of snow surface melt. In wind protected areas near treeline and below treeline, snow surface melt occurred rapidly. At 12:30 pm, ankle deep boot penetration was noted in above treeline terrain at 8,500' on a wind exposed SW aspect. Much deeper boot penetration could easily be found in wind sheltered areas at that same time. At 12:45 pm, unsupportable snow surface conditions were observed on wind protected S aspects at treeline at 8,000'. Overall, the rate of snow surface melt and development of surface wet snow instability was greatly influenced by exposure to wind in any given location (photo, more info).

Weather and CURRENT CONDITIONS
weather summary

One more day of sun, wind, and well above freezing air temperatures is forecast for today ahead of an approaching cold front. A significant cool down and a period of light snowfall is expected for Monday. This morning, remote sensors above 8,000' are reporting air temperatures in the upper 20s to mid 30s. This is about 5 degrees colder than 24 hours ago. Maximum daytime air temperatures will be about 5 degrees colder today than yesterday. Areas above 7,000' are forecast to reach the upper 30s to upper 40s today. Ridgetop winds remain out of the southwest to west this morning and are moderate in speed. Moderate to strong southwest to west winds are forecast to continue through tomorrow.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 29 to 36 deg. F.
Max. temperature in the last 24 hours: 41 to 50 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 41 mph
Maximum wind gust in the last 24 hours: 62 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 38 to 80 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy skies. Partly cloudy skies becoming mostly cloudy. Isolated snow showers in the evening. Scattered snow showers after midnight. Mostly cloudy skies with a chance of snow showers in the morning. Snow showers likely in the afternoon.
Temperatures: 44 to 50 deg. F. 21 to 28 deg. F. 31 to 39 deg. F.
Wind Direction: SW SW W
Wind Speed: 20 to 25 mph with gusts to 40 mph. 20 to 30 mph with gusts to 40 mph. 15 to 25 mph with gusts to 35 mph.
Expected snowfall: 0 in. 0 to trace in. Up to 2 in.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy skies. Partly cloudy skies becoming mostly cloudy. Isolated snow showers in the evening. Scattered snow showers after midnight. Mostly cloudy skies with a chance of snow showers in the morning. Snow showers likely in the afternoon.
Temperatures: 37 to 45 deg. F. 16 to 23 deg. F. 26 to 32 deg. F.
Wind Direction: W W W
Wind Speed: 35 to 40 mph with gusts to 65 mph. 35 to 45 mph with gusts to 65 mph. 30 to 40 mph with gusts to 55 mph.
Expected snowfall: 0 in. 0 to trace 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.