THIS AVALANCHE ADVISORY EXPIRED ON February 11, 2017 @ 6:59 am
Avalanche Advisory published on February 10, 2017 @ 6:59 am
Issued by Andy Anderson - Tahoe National Forest

Large human-triggered wind slab avalanches remain likely today due to gale force winds and heavy snow across the forecast area. Today the avalanche danger is CONSIDERABLE in near and above treeline terrain and MODERATE in below treeline. Dangerous avalanche conditions exist. Carefully evaluate the terrain and snowpack before committing to any slope and use this information plan conservative travel routes that avoid the avalanche problems. 

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Strong winds and 12 to 20 inches of new snow in the last 24 hours have formed large wind slabs on wind-loaded aspects. The largest and most fragile wind slabs will exist on wind-loaded N-NE-E aspects and cross-loaded SE and NW aspects above 7500 ft. where the most snow has accumulated. Due to the strength of the wind and the changing wind direction between SW-S-SE, some wind slabs could exist in below treeline terrain as well as near and above treeline terrain on almost any aspect. More snow and wind across the forecast area today and lowering snow levels mean that wind slabs will continue to grow and become more widespread today. While the best window for natural wind slab avalanches likely occurred during the night, human triggered wind slab avalanches will remain likely on any wind-loaded slopes today.

Looks for signs of recent wind loading such as cornices, blowing snow, wind drifts, wind pillows, ripples on the snow surface, and other wind created textures to help identify where wind slabs may exist and use this information to avoid these problematic wind slabs.

recent observations

Yesterday observations on Tamarack Peak before the onset of heavy precipitation found evidence of widespread rain up to at least 9500 ft. and likely a bit higher. Refreezing rain crusts existed on all aspects and elevations. Some areas had small amounts of new snow on top of the crusts and the strong winds had already started to form small wind slabs by 11:00 am yesterday even though less than an inch of new snow had fallen by that time. Intense precipitation became widespread across the forecast area by 12:30 pm. yesterday. 

Weather and CURRENT CONDITIONS
weather summary

2.5 to 4.5 inches of precipitation has fallen across the forecast area since yesterday morning. Below 7500 ft. most of this precip fell as rain with a few lower elevation sensors reporting up to 12 inches of new snow in areas where snow levels fell a little sooner. Above 7500 ft. 12 to 20 inches of heavy snow has accumulated. Snow levels remained between 7500 and 8000 ft for much of the night before dropping to around 7000 ft. early this morning. Snow levels should continue to hover between 6000 and 7000 ft. today. Gale force southwest winds accompanied this storm. These winds should decrease some today and continue to decrease tonight, but they will still remain strong enough to transport snow. The main part of the storm should move south of the forecast area today. While the precipitation should start to decrease today, the forecast still calls for continued snow today with another 3 to 10 inches of accumulation predicted for areas above 7000 ft. Snow should taper off tonight as the remnants of the storm depart. By tomorrow, high pressure should begin to build over the region causing the winds to shift to the east and northeast. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 26 to 32 deg. F.
Max. temperature in the last 24 hours: 37 to 42 deg. F.
Average wind direction during the last 24 hours: Southwest to southeast
Average wind speed during the last 24 hours: 55 to 65 mph
Maximum wind gust in the last 24 hours: 145 mph
New snowfall in the last 24 hours: 12 to 20 inches
Total snow depth: 122 to 167 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 snow and rain. Snow level lowering to Lake level or below today. Cloudy with snow showers in the evening. Snow showers decreasing after midnight Partly cloudy with a slight chance of snow
Temperatures: 35 to 41 deg. F. 19 to 24 deg. F. 28 to 33 deg. F.
Wind Direction: Southwest West East
Wind Speed: 15 to 25 mph with gusts to 45 mph 15 to 20 mph with gusts to 40 mph decreasing to 30 mph after midnight 10 to 15 mph with gusts to 35 mph in the afternoon
Expected snowfall: 3 to 10 in. 2 to 4 in. up to 1 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Snow Cloudy with snow showers in the evening. Snow showers decreasing after midnight Partly cloudy with a slight chance of snow
Temperatures: 30 to 36 deg. F. 16 to 21 deg. F. 23 to 28 deg. F.
Wind Direction: Southwest Southwest shifting to the west after midnight Northeast
Wind Speed: 25 to 35 mph with gusts to 85 mph 25 to 35 mph with gusts to 75 mph decreasing to 15 to 25 mph with gusts to 55 mph after midnight 10 to 15 mph with gusts to 25 mph increasing to 20 to 30 mph with gusts to 55 mph in the afternoon
Expected snowfall: 3 to 10 in. 2 to 4 in. up to 1 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