THIS AVALANCHE ADVISORY EXPIRED ON April 9, 2016 @ 7:00 am
Avalanche Advisory published on April 8, 2016 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE danger already exists on slopes steeper than 35 degrees on all aspects and elevations due to the presence of unfrozen loose wet snow. MODERATE danger will persist throughout the day as more loose wet snow forms resulting from daytime warming and rain impacting the area. Loose wet avalanches large enough to threaten backcountry travelers will be possible again today. Evaluate snow and terrain carefully. Identify and avoid the areas where wet snow deep enough for loose wet avalanches exists. 

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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  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Some cloud cover last night and overnight lows well above freezing should have prevented much of a refreeze from occurring. If any of yesterday's wet snow did refreeze, it will not stay frozen long. Today's warm temperatures, some morning sunshine, and some afternoon rain will allow wet snow to form on all aspects. Once the snowpack becomes wet, it becomes weak since the ice bonds that give the snowpack strength will have melted away leaving deep, loose, wet snow sitting on the slopes. Loose wet avalanches will be possible on slopes steeper than 35 degrees wherever loose wet snow exists. Loose wet activity will become possible on the E-SE-S-SW-W aspects at all elevations first and then progress to the NW-N-NE aspects as they warm up a little later. Once it starts raining, loose wet avalanches will be possible on any slopes where the rain falls. Most of the wet snow instabilities should manifest as loose wet avalanches but other forms of wet snow instabilities like glide cracks or wet slabs are not impossible. 

Due to a lack of overnight refreeze, expect the snowpack to become unsupportable earlier today than on previous days. In some areas it may already be unsupportable since it never refroze. As soon as an unsupportable snowpack exists, it is time to move to more frozen aspects if they are available, onto lower angle slopes away from anything steep, or to head for an activity that does not involve snow.

Stepping off your equipment and sinking into wet snow above your boot tops and small surface instabilities like roller balls, pinwheels, or point releases can provide clues that enough wet snow has formed for larger loose wet avalanches to become an issue. Terrain traps like gullies, creeks, and cliffs can greatly increase the risk of any size loose wet avalanches.

recent observations

Yesterday observations on Castle Peak found that after a very short window of supportable corn conditions before 10:30 am, the snowpack started becoming unsupportable on the sun-exposed E-SE-S aspects as early as 10:30 am. Ski kicks on test slopes triggered loose wet avalanches that entrained 6 to 8 inches of wet snow on E aspects at 8100 ft. by 11:00 am. Shortly after this time, SW-W aspects that had held supportable melt freeze conditions also started to become unsupportable. By noon boot top deep wet snow also existed on these aspects, and ski cuts triggered similar loose wet avalanches. These deep wet snow conditions existed up to at least 8600 ft. by midday. Northerly aspects held supportable melt freeze conditions with 1-3 inches of wet snow resting on top of frozen crusts and transitional snow at noon. One large cornice collapse had occurred on a wind loaded NE aspect within the last 2 days, and craks had formed on the ridgelines behind the remaining cornices. 

Weather and CURRENT CONDITIONS
weather summary

A low pressure system near southern CA should push more cloud cover and moisture into the forecast area today. Chances of some light precipitation will increase throughout the day. The forecast calls for a chance of rain this afternoon and evening with the rain showers becoming more widespread late tonight and into tomorrow. Areas south of Hwy 50 hold the best chances for precipitation today. The precipitation should spread farther north across the whole forecast area tonight and tomorrow. Snow level should remain above 9000 ft. today and tonight before dropping toward 8000 ft. late Saturday. Overall .3 to .8 inches of precipitation could fall by tomorrow afternoon mostly in the form of rain. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 37 to 43 deg. F.
Max. temperature in the last 24 hours: 49 to 56 deg. F.
Average wind direction during the last 24 hours: East to southwest
Average wind speed during the last 24 hours: 15 to 20 mph
Maximum wind gust in the last 24 hours: 37 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 64 to 108 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Partly cloudy becoming cloudy with a chance of rain showers especially in the afternoon and a slight chance of thunderstorms. Snow level 9500 ft. to 10000 ft. Cloudy with a slight chance of thunderstorms in the evening and widespread rain showers through the night. Snow level above 9000 ft. Cloudy with showers likely in the morning and a slight chance of thunderstorms in the afternoon. Snow level dropping to around 8000 ft. by the afternoon.
Temperatures: 50 to 57 deg. F. 28 to 35 deg. F. 39 to 46 deg. F.
Wind Direction: East South Southwest
Wind Speed: Light Light Light
Expected snowfall: Rain: 0 to .1 in. Rain: .1 to .3 in. Rain: .2 to .4 inches | Above snow level, snow: up to 2 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Partly cloudy becoming cloudy with a chance of rain showers especially in the afternoon and a slight chance of thunderstorms. Snow level 9500 ft. to 10000 ft. Cloudy with a slight chance of thunderstorms in the evening and widespread rain showers through the night. Snow level above 9000 ft. Cloudy with showers likely in the morning and a slight chance of thunderstorms in the afternoon. Snow level dropping to around 8000 ft. by the afternoon.
Temperatures: 49 to 55 deg. F. 26 to 33 deg. F. 35 to 42 deg. F.
Wind Direction: East South Southwest
Wind Speed: 15 to 25 mph with gusts to 40 mph decreasing to 30 mph in the afternoon 15 to 20 mph with gusts to 30 mph 10 to 15 mph
Expected snowfall: Rain: 0 to .1 inches | Above snow level, snow: up to 1 in. Rain: .1 to .3 inches | Above snow level, snow: up to 3 in. Rain: .2 to .4 inches | Above snow level, snow: up to 4 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.

For a recorded version of the Avalanche Advisory call (530) 587-3558 x258