THIS AVALANCHE ADVISORY EXPIRED ON March 15, 2015 @ 6:57 am
Avalanche Advisory published on March 14, 2015 @ 6:57 am
Issued by Brandon Schwartz - Tahoe National Forest

Avalanche danger is MODERATE for all elevations and aspects on slopes 37 degrees and steeper due to a suspected poor overnight snow surface refreeze and subsequent loose wet and wet slab avalanche concerns. Continuous snow cover on SE-S-SW-W aspects sufficient to allow for avalanche activity exists only in isolated areas.

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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Due to cloud cover and above freezing air temperatures last night, a poor to nonexistent overnight snow surface refreeze is expected. In areas where breaks in cloud cover allowed for a short window of radiational cooling, any snow surface refreeze that did form is expected to be superficial, thin, and weak. As daytime warming progresses, areas of wet surface snow will become widespread in the vast majority of areas. The lack of snow cover remaining on most SE-S-SW-W aspects will limit instability that forms today on those aspects to the isolated areas of continuous snow cover. Of the slopes with continuous snow cover, E aspects will hold the greatest amount of wet snow with carry over from yesterday that did not refreeze last night. Lesser amounts of wet snow will exist on NW-N-NE aspects. Human triggered loose wet avalanches are possible today on slopes 37 degrees and steeper. Keep in mind that secondary terrain hazards such as cliffs and terrain traps below hold the potential to greatly magnify consequences of an avalanche that would otherwise be too small to bury or injure a person.

Avalanche Problem 2: Wet Slab
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Wet slab avalanches are an unlikely but not impossible avalanche problem today above 7,000' to 7,500' on NW-N-NE aspects on slopes 37 degrees and steeper. Areas where the snowpack remains transitional with wet snow over old snow unaffected by melt freeze are the most likely locations for a wet slab avalanche to occur. Hand pits will easily identify areas where wet surface snow sits over dry old snow below. Deep ski or boot penetration in these areas is cause for concern. If this becomes the situation, avoid the hazard by changing aspects and/or moving to low angle terrain without steeper terrain above. 

recent observations

Observations made yesterday on the north side of Carson Pass revealed a well established spring type snowpack on E aspects. Snowpit data indicated a very strong and supportable rain and melt-freeze crust exists in the top 12 inches of the snowpack with well drained melt forms below. The snowpack was noted as approaching isothermal at the snowpit site (E aspect, 8,900'). Several ski cuts on steep E aspect test slopes between noon and 12:30 pm produced only minor roller balls. No significant evidence of wet snow instability was observed prior to departing this area at 1 pm. Surface snow on NE aspects adjacent to the E aspect mentioned above was more transitional and less supportive. Melt-freeze crust on the NE aspects was more superficial with softer, old snow unaffected by melt-freeze below it. Glossary of terms

Around the forecast area in general, significant melt out has occurred on most SE-S-SW-W aspects. On these aspects large areas of bare ground exist with a few sizable snow patches remaining in isolated locations. In general, continuous snow cover is limited to NW-N-NE-E aspects.

 

Weather and CURRENT CONDITIONS
weather summary

The ridge of high pressure over the forecast area is shifting just enough to allow for cloud cover and increasing southwest winds to impact the forecast area as moisture streams by to the north. Remote sensors are reporting air temperatures this morning in the 40s between 7,000' and 9,600' under mostly cloudy skies. Moderate speed southwest winds have mixed the atmosphere, keeping the overnight formation of inversion conditions to a minimum. Maximum daytime air temperatures are forecast to reach into the 50s again today for areas above 7,000'. Southwest winds will increase in speed as the day progresses, becoming strong this afternoon. For tomorrow, a slight chance of precipitation exists for the far northern portion of the forecast area. For most areas expect continued cloud cover, warm air temperatures, and strong southwest winds.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 40 to 45 deg. F.
Max. temperature in the last 24 hours: 52 to 57 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 19 mph
Maximum wind gust in the last 24 hours: 31 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 24 to 44 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy skies. Mostly cloudy skies. Mostly cloudy skies.
Temperatures: 51 to 58 deg. F. 36 to 43 deg. F. 50 to 56 deg. F.
Wind Direction: SW SW SW
Wind Speed: 15 to 20 mph with gusts to 30 mph, increasing to 30 to 35 mph with gusts to 55 mph in the afternoon. 30 to 40 mph with gusts to 60 mph. 35 to 45 mph with gusts to 65 mph.
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy skies. Mostly cloudy skies. Mostly cloudy skies.
Temperatures: 50 to 56 deg. F. 35 to 42 deg. F. 46 to 52 deg. F.
Wind Direction: SW SW SW
Wind Speed: 20 to 25 mph with gusts to 40 mph, increasing to 40 to 45 mph with gusts to 65 mph in the afternoon. 40 to 50 mph with gusts to 75 mph. 45 to 55 mph with gusts to 85 mph.
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.