THIS AVALANCHE ADVISORY EXPIRED ON April 13, 2013 @ 6:32 am
Avalanche Advisory published on April 12, 2013 @ 6:32 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 near or below freezing air temperatures and radiational cooling of the upper snowpack under clear skies. As daytime warming progresses, surface wet snow instability will develop. 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. 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 Tamarack Peak (Mount Rose area) revealed that snow level Wednesday night had been around 8,300' in that area. Minimal new snow amounts of a trace to nearly 1 inch of new snow had accumulated. By mid day, this new snow was quickly assimilating with the melt-freeze snow below on all but true north aspects above 9,500'. At 1 pm, a very small and very minor intentionally skier triggered loose wet avalanche occurred on the E aspect Proletariat Face at 9,700' in a pocket of 40 degree slope angle near treeline terrain (photos, more info). The avalanche involved only the top 1 inch of the snowpack, but indicated that a few more inches of wet surface snow could become involved in human triggered loose wet avalanches later in the afternoon and evening hours.

Weather and CURRENT CONDITIONS
weather summary

High pressure is in place over the forecast area. Sunny skies this morning will give way to party cloudy skies this afternoon. Ridgetop winds are decreasing in speed this morning and are expected to shift from E to S today. Winds are forecast to shift to the SW by this evening, increasing in speed overnight into tomorrow. Remote sensors are reporting air temperatures above 8,000' in the upper 20s to mid 30s this morning. Maximum daytime air temperatures for areas above 7,000' are forecast to reach the upper 40s to upper 50s today, about 5 degrees warmer than yesterday.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 30 to 34 deg. F.
Max. temperature in the last 24 hours: 44 to 51 deg. F.
Average wind direction during the last 24 hours: E
Average wind speed during the last 24 hours: 18 mph
Maximum wind gust in the last 24 hours: 32 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 42 to 82 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Sunny skies, becoming partly cloudy. Partly cloudy skies. Partly cloudy skies.
Temperatures: 50 to 57 deg. F. 29 to 36 deg. F. 51 to 57 deg. F.
Wind Direction: E SW SW
Wind Speed: Light winds increasing to 10 to 15 mph in the afternoon. 10 to 15 mph. 20 to 30 mph with gusts to 35 mph. Gusts increasing to 45 mph in the afternoon.
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Sunny skies, becoming partly cloudy. Partly cloudy skies. Partly cloudy skies.
Temperatures: 48 to 54 deg. F. 30 to 37 deg. F. 45 to 53 deg. F.
Wind Direction: E shifting to S SW SW
Wind Speed: Light winds shifting and increasing to 10 to 15 mph in the afternoon. 15 to 20 mph with gusts to 30 mph. 30 to 35 mph with gusts to 50 mph, increasing to 40 to 45 mph with gusts to 65 mph in the afternoon.
Expected snowfall: 0 in. 0 in. 0 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.