THIS AVALANCHE FORECAST EXPIRED ON February 13, 2019 @ 6:59 am
Avalanche Forecast published on February 12, 2019 @ 6:59 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

MODERATE avalanche danger exists in near and above treeline terrain due to wind slab avalanche problems. Human-triggered avalanches will remain possible today. Expect avalanche conditions to become more complex and dangerous as a winter storm arrives tomorrow.  

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.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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    Certain
    Very Likely
    Likely
    Possible
    Unlikely
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    Historic
    Very Large
    Large
    Small

Wind slabs and cornices will grow in size and extent on near and above treeline NW-N-NE-E-SE aspects as the intense SW winds continue. New, firm, dense wind slabs now exist on top of older wind slabs. Some wind slabs may be stubborn (difficult to trigger) and some may be more sensitive. Human-triggered wind slab avalanche activity will remain possible today. Some of the wind slabs could break above the person on the slope. Areas with trigger points, where the wind slabs are thinner, and unsupported slopes represent terrain where triggering a wind slab could be easier.

Identify where wind slabs may exist by using clues like blowing snow, cornices above a slope, firm hollow-sounding snow, and wind features on the snow surface. Use this information to manage your group and implement appropriate safety margins. Traveling in terrain sheltered from the winds could lead to softer more consistent snow conditions with less potential for wind slab problems.

recent observations

* Yesterday observations from Tallac and Tamarack found windy conditions in exposed areas with intense blowing snow and dense wind slab formation near ridges. On Tamarack ski kicks on wind-loaded test slopes revealed stubborn firm wind slabs that would only crack if the slope was undercut. Cornices remained fragile and sensitive to skier triggering.

* In more sheltered areas on Tallac and Tamarack, observers did not report any signs of instability. Soft snow did exist in the sheltered areas. Snowpit data on different aspects of Tamarack showed a strengthening snowpack.

Weather and CURRENT CONDITIONS
weather summary

Southwest winds increased overnight and should continue to increase as the next winter storm approaches the region. Cloud cover should also start building today. Precipitation could commence as early as this afternoon but is more likely to begin this evening with a small amount of new snow overnight. By tomorrow heavy snow and rain should impact the forecast area and continue through Thursday with 5-7 inches of water expected to accumulate along the Sierra Crest in some form by the end of Thursday. The forecast calls for snow levels to start around 4000 ft this afternoon and then increase to somewhere between 6500 ft and 8000 ft by tomorrow afternoon. Significant uncertainty exists concerning the timing and exact elevation of snow levels. Check in with the Reno NWS for more details about this complex storm.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 14 to 24 deg. F.
Max. temperature in the last 24 hours: 17 to 24 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 30 to 35 mph
Maximum wind gust in the last 24 hours: 79 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 99 to 124 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Partly cloudy then becoming mostly cloudy. Slight chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 15%. Cloudy. Chance of snow in the evening, then snow after midnight. Snow levels below 7000 feet. Chance of precipitation is 70%. Cloudy. Rain and snow. Snow levels below 7000 feet increasing to 8000 feet in the afternoon. Chance of precipitation is 100%.
Temperatures: 29 to 34 deg. F. 22 to 27 deg. F. 34 to 39 deg. F.
Mid Slope Winds: Southwest 15 to 20 mph with gusts to 40 mph increasing to 15 to 30 mph with gusts to 60 mph in the afternoon. Southwest 25 to 40 mph with gusts to 85 mph. South 25 to 35 mph with gusts to 75 mph.
Expected snowfall: No accumulation. | SWE = trace amounts. 60% probability of 2 to 4 inches. 40% probability up to 2 inches. | SWE = 0.15-0.25 inch. 90% probability of 6 to 12 inches. 10% probability of 10 to 15 inches. | SWE = 0.95-1.40 inches.
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Partly cloudy then becoming mostly cloudy. Slight chance of snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 15%. Cloudy. Chance of snow in the evening, then snow after midnight. Snow levels below 7000 feet. Chance of precipitation is 75%. Cloudy. Snow through the day. Rain in the afternoon. Snow levels below 7000 feet increasing to 8000 feet in the afternoon. Chance of precipitation is 100%.
Temperatures: 25 to 31 deg. F. 20 to 25 deg. F. 31 to 37 deg. F.
Ridge Top Winds: Southwest 25 to 35 mph with gusts to 80 mph increasing to 30 to 50 mph with gusts to 100 mph in the afternoon. Southwest 35 to 55 mph with gusts to 100 mph. Southwest 40 to 60 mph. Gusts up to 110 mph increasing to 130 mph in the afternoon.
Expected snowfall: No accumulation. | SWE = trace amounts. 60% probability of 2 to 5 inches. 40% probability up to 2 inches. | SWE = up to 0.30 inch. 90% probability of 8 to 14 inches. 10% probability of 12 to 18 inches. | SWE = 1.00-1.50 inches.
Disclaimer

This avalanche forecast is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This forecast 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 forecast applies only to backcountry areas outside established ski area boundaries. This forecast describes general avalanche conditions and local variations always occur. This forecast expires 24 hours after the posted time unless otherwise noted. The information in this forecast is provided by the USDA Forest Service who is solely responsible for its content.

For a recorded version of the avalanche forecast call (530) 587-3558 x258