THIS AVALANCHE FORECAST EXPIRED ON April 8, 2017 @ 7:01 am
Avalanche Forecast published on April 7, 2017 @ 7:01 am
Issued by Andy Anderson - Tahoe National Forest

HIGH avalanche danger exists in near and above treeline terrain with CONSIDERABLE danger in below treeline areas due to wind slabs and storm slabs. Natural and human triggered avalanches are very likely today. Dangerous avalanche conditions exist in the backcountry today. Travel in avalanche terrain is not recommended.

4. High

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Above Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

4. High

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Near Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
Avalanche Problem 1: Wind Slab
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New snow and gale force southwest winds during the storm have created problematic wind slabs on wind-loaded slopes. As more snow and wind impact the forecast area today, these wind slabs will become larger and more widespread. Human triggered and natural wind slab avalanches will be likely today. Some of these wind slabs will be deep, large, and would have very serious consequences. The largest and most fragile wind slabs will exist on the wind loaded N-NE-E aspects and on cross-loaded NW and SE aspects in near and above treeline terrain, but wind slabs could also exist in some below treeline areas due to the strength of the winds. 

Identify where wind slabs might exist by using clues like blowing snow, wind drifts, cornices above slopes, wind-created ripples, and other wind created features. Use this information to avoid the wind slabs.

Avalanche Problem 2: Storm Slab
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Changing snow levels and accumulation rates will create weak layers and slab layers within the storm snow. Human triggered storm slab avalanches will be likely today and some natural storm slab avalanches may be possible. Storm slabs could exist on steep slopes in non-wind-affected terrain and could involve enough snow to bury or injure a person. The areas that receive the most new snow and highest snowfall rates will represent the best places to find storm slabs. Storm slabs and/or loose wet snow instabilities will also be likely in any areas where rain falls on new snow.

Recent avalanche activity, shooting cracks, snowpits, and probing can all help identify where storm slabs may exist. Use this information to avoid steep slopes where storm slabs may exist. 

Forecast discussion

Due to uncertainty concerning snowfall amounts the avalanche hazards could vary greatly from place to place. In areas that receive the high end of forecasted snow amounts, more avalanche danger and larger avalanche problems will exist. In areas where snow totals only reach the low end of the forecasted accumulation, the avalanche problems could be smaller and less widespread.

recent observations

Observations on Elephant's Hump at Carson Pass yesterday found wet snow with minor amounts of new snow on the surface. Strong winds and blowing snow had already formed small wind slabs (up to 6 inches deep) on some wind-loaded slopes. Ski cuts on wind-loaded test slopes did not trigger shooting cracks or slab failures but did result in some loose wet snow instabilities. Overall the snowpack appeared to be ready to handle the new snow load.

Weather and CURRENT CONDITIONS
weather summary

Rain and snow started to impact the forecast area yesterday as the storm arrived. The heavy precipitation started in the evening and continued through the night. So far 1.5 to 2.5 inches of water equivalent has fallen on the forecast area. Snow levels bounced between 6000 and 8500 ft. until around midnight when they dropped to between 6000 and 6500 ft. Above 8000 ft. 10 to 15 inches of new snow has accumulated with 6 to 8 inches in areas between 6500 and 8000 ft. Snow levels should continue to hover between 6000 and 7000 ft. today and could jump into the 7500 ft. range at times. As more cold air moves into the area tonight and tomorrow, they should fall to below 6000 ft. Hurricane force southwest winds have pummelled the mountains since the start of the storm. Snow and hurricane force southwest winds should continue today with heavy precipitation across the region this morning. The storm may decrease in intensity some this afternoon before another round of increased winds and intense precipitation impacts the forecast area this evening and through the night. The storm should start to decrease in intensity during the day tomorrow. The forecast calls for  10 to 28 inches of new snow accumulation by tomorrow afternoon above 7000 ft. with a slight chance of significantly higher snow totals (up to 3-4 ft). For more details and the most up to date information on this storm check in with the Reno NWS.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 25 to 32 deg. F.
Max. temperature in the last 24 hours: 33 to 40 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 60 to 70 mph
Maximum wind gust in the last 24 hours: 134 mph
New snowfall in the last 24 hours: 10 to 15 inches
Total snow depth: 124 to 182 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Cloudy with a mix of snow and rain. Snow levels between 6000 and 7500 ft. Cloudy with rain in the evening and snow during the night. Snow levels starting between 6000 and 7500 ft and dropping to below 6000 ft. during the night Cloudy with snow in the morning. Snow decreasing and becoming snow showers in the afternoon
Temperatures: 35 to 40 deg. F. 21 to 26 deg. F. 25 to 30 deg. F.
Winds: Southwest Southwest Southwest
Expected snowfall: Depending on snow levels: 2 to 12 in. Depending on snow levels:4 to 14 in. 3 to 6 in. with a chance of 6 to 10 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Snow Snow Cloudy with snow in the morning. Snow decreasing and becoming snow showers in the afternoon
Temperatures: 31 to 37 deg. F. 16 to 22 deg. F. 21 to 27 deg. F.
Winds: Southwest Southwest Southwest
Expected snowfall: 6 to 12 in. with a slight chance of 10 to 18 in. 4 to 10 in. with a chance of 10 to 16 in. 3 to 8 in. with a slight chance of 8 to 12 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