THIS AVALANCHE FORECAST EXPIRED ON April 18, 2018 @ 7:00 am
Avalanche Forecast published on April 17, 2018 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE avalanche danger exists at all elevations today due to rapid warming allowing loose wet avalanches to become possible and lingering wind slabs on wind-loaded slopes. The April sun will help destabilize the snowpack and conditions could change in a matter of minutes once the sun hits the new snow. Once any signs of warming snow or wet snow exist it is time to move to colder aspects, lower angle slopes, or switch an activity that does not involve snow.

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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Even though temperatures should remain slightly below normal today, intense April sunshine on the new snow will cause enough warming for wet snow instabilities to form. Human-triggered roller balls, pinwheels, and loose wet avalanches are possible on steep slopes today. Some natural loose wet instabilities may occur on the most sun-exposed slopes near rocks or trees as well. These loose wet instabilities could entrain most of the new snow and could injure a person. They may even involve enough snow to bury a person if they occur in an area with terrain traps or where the most new snow exists. Due to the high sun angles and intense sunshine, loose wet instabilities could occur on any aspect today.

As soon as the sun hits the new snow today wet snow will start to form on the surface. Conditions will change quickly from cold soft snow to sunny warm unstable snow. Once the snow starts to feel wet and sticky or small signs of loose wet instabilities like small roller balls or pinwheels start to occur, it is time relocate to a colder aspect or abandon the snow for a different afternoon activity.

Avalanche Problem 2: Wind Slab
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Human-triggered wind slab avalanches will remain possible today on wind-loaded N-NE-E aspects and cross-loaded NW, SE, and S aspects in near and above treeline terrain. Some of these could entrain enough snow to bury or injure a person. As the intense April sun warms up the new snow, it will also make wind slabs easier to trigger especially on sun-exposed E-SE-S facing slopes. 

Clues like cornices above a slope, drifted snow, ripples in the snow surface, and other wind created features can help identify where these wind slabs may exist. Use this information to avoid the wind slabs and seek out more sheltered slopes.

recent observations

* Yesterday observations found fragile cornices above wind loaded slopes on Andesite Ridge (Donner Summit area) and along ridgelines near Heavenly. Ski and snowboard cuts on wind loaded test slopes triggered small wind slabs and some shooting cracks on Andesite Peak and in the Carson Pass area.

* Even though the sun only came out for short periods of time yesterday, warm wet snow formed on the surface on E aspects of Andesite Peak as soon as the sun hit the slopes. Ski kicks triggered a shallow surface slab on an E aspect that had just experienced sunshine on Andesite and some roller balls were reported on E aspects near Heavenly in the afternoon. 

* On steep more northerly slopes on Carson Pass, some loose snow sluffing occurred during the day.

* The new snow rested on top of a mix of firm crusts on Carson Pass and moist crusts on Donner Summit. 

Weather and CURRENT CONDITIONS
weather summary

Showers throughout the day yesterday deposited another 2 to 6 inches of snow across the forecast area. These showers came to an end and skies cleared overnight. Sunny weather returns today and temperatures should warm about 5 to 10 degrees above yesterday but still remain somewhat cool for this time of year. Cloud cover and SW winds should begin to increase tonight ahead of another system approaching the area Wednesday afternoon and overnight on Wednesday. This main impacts of this storm should stay south of the region but some light snow showers could start to occur tomorrow afternoon.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 12 to 19 deg. F.
Max. temperature in the last 24 hours: 25 to 30 deg. F.
Average wind direction during the last 24 hours: SW shifting to NE after midnight
Average wind speed during the last 24 hours: 10 to 20 mph
Maximum wind gust in the last 24 hours: 58 mph
New snowfall in the last 24 hours: 2 to 6 inches
Total snow depth: 56 to 99 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny Partly cloudy becoming mostly cloudy Mostly cloudy with a slight chance of snow showers in the afternoon
Temperatures: 36 to 42 deg. F. 19 to 24 deg. F. 36 to 42 deg. F.
Mid Slope Winds: Variable Variable Southwest
Wind Speed: Light Light with gusts to 25 mph after midnight Light in the morning increasing to 10 to 15 mph with gusts to 35 mph in the afternoon
Expected snowfall: 0 0 trace
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny Partly cloudy becoming mostly cloudy Mostly cloudy with a slight chance of snow showers in the afternoon
Temperatures: 30 to 36 deg. F. 17 to 22 deg. F. 28 to 36 deg. F.
Ridge Top Winds: Variable South Southwest
Wind Speed: Light Light increasing to 10 to 15 mph with gusts to to 40 mph after midnight 20 to 30 mph with gusts to 60 mph
Expected snowfall: 0 0 trace
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

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