THIS AVALANCHE ADVISORY EXPIRED ON March 6, 2016 @ 7:00 am
Avalanche Advisory published on March 5, 2016 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE avalanche danger exists on all aspects and elevations today due to newly formed wind slabs on wind loaded slopes above 8000 ft. and rain on snow creating loose wet snow instabilities on slopes below 8000 ft. Human triggered avalanches will be possible today.

Expect the avalanche danger to rise quickly as the next storm impacts the region tonight. Periods of HIGH avalanche danger may occur tonight as natural wind slab avalanches and storm slab avalanches become likely after midnight. 

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: Wind Slab
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New snow and wind during the night allowed new wind slabs to form on wind-loaded and cross-loaded slopes that received snow instead of rain. These wind slabs will continue to grow as more snow and wind impact the forecast area today. While many of these wind slabs may remain relatively small, some of these slabs could measure 18 to 36 inches in depth in heavily wind loaded areas. These wind slabs may have a layer of lighter, colder, weaker snow that fell during the night at their base. Human triggered wind slabs will be possible today on wind loaded N-NE-E aspects and cross-loaded NW and SE aspects above 8000 ft. in near and above treeline terrain where more of the precipitation has fallen as snow. 

As the second storm impacts the region tonight, wind slabs will quickly become large, and natural avalanche activity involving these large new wind slabs will be likely after midnight tonight.  Storm slab avalanches may also occur in non wind-loaded areas tonight due to the intense snowfall rates and changing conditions during the storm. 

Avalanche Problem 2: Loose Wet
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Rain on snow may trigger more loose wet avalanche activity below 8000 ft. today. The NW-N-NE aspects will represent the best places to find loose wet snow avalanches since the snow on these aspects has not transitioned to corn snow, and it has not developed good drainage channels. Small loose wet snow instabilities like roller balls, pinwheels, and point releases should represent the majority of the loose wet snow problems today, but some larger loose wet snow avalanches may occur on those northerly aspects. Smaller more isolated loose wet snow instabilities may still form on isolated terrain features on the E-SE-S-SW-W aspects below 8000 ft. 

recent observations

Yesterday observations from Donner Ridge (Donner Summit area) and Incline Lake Peak (Mt. Rose backcountry) showed a snowpack that should handle new snow loading well. Below the surface snowpit tests did not find any signs of instability. On the snow surface, observations showed warm wet snow on all aspects up to about 9000 ft. on Incline Lake Peak and up to the summit of Donner Ridge. Some small human triggered pinwheels did occur on NE-ENE aspects below 9000 ft. on Incline Lake Peak. 

Weather and CURRENT CONDITIONS
weather summary

Last night's storm provided 1 to 2 inches of water to the region. Below 8000 ft most of this fell as rain with 1 to 2 inches of heavy snow mixed in during the night. Above 8000 ft. 4 to 8 inches of heavy snow accumulated. This snow was mixed with some rain at times up to 8700 ft. Snow levels have been bouncing between ~8700 ft. at the highest and ~7100 ft. during the heaviest precipitation. Snow levels should remain ~8000 ft. today and into this evening. By tomorrow morning snow levels should have fallen below 5000 ft. The forecast calls for light precipitation to continue for most of today with up to 5 more inches of snow at the upper elevations and mostly rain below 8000 ft. By this afternoon the southwest winds should increase as a stronger winter storm approaches the area. The bulk of the storm should arrive over the region tonight and will bring heavy precipitation and gale force southwest winds. Since snow level will start at or above 8000 ft. some of this precipitation could fall as rain. A cold front accompanying this storm will push snow levels down quickly and snow totals could reach 9 to 15 inches between 7000 and 8000 ft and 13 to 25 inches above 8000 ft. by tomorrow morning. Snowfall and strong southwest winds should continue through the day tomorrow with another 4 to 6 inches of snow expected tomorrow. Another storm in this series should arrive Sunday night. Check in with the Reno NWS for more details.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 31 to 34 deg. F.
Max. temperature in the last 24 hours: 38 to 43 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 35 mph
Maximum wind gust in the last 24 hours: 59 mph
New snowfall in the last 24 hours: 4 to 8 inches
Total snow depth: 61 to 87 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy with rain and snow in the morning and mostly rain in the afternoon. Snow level around 8000 ft. Cloudy with rain in the evening and snow after midnight. Snow level starting at 8000 ft. and falling below 5000 ft. by Sunday morning. Snow
Temperatures: 40 to 47 deg. F. 18 to 25 deg. F. 27 to 34 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 35 to 40 mph with gusts to 55 mph increasing to 45 to 50 mph with gusts to 65 mph in the afternoon 45 to 55 mph with gusts to 75 mph 25 to 35 mph with gusts to 55 mph
Expected snowfall: Rain: .5-.6 in. | Snow: up to 3 in. 6 to 12 in. 4 to 6 in.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy with snow in the morning and a mix of rain and snow in the afternoon. Snow levels around 8000 ft. Cloudy with a mix of rain and snow in the evening changing to snow after 10 pm. Snow level starting at 8000 ft. and falling below 5000 ft. by Sunday morning. Snow
Temperatures: 36 to 43 deg. F. 16 to 23 deg. F. 23 to 30 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 50 to 55 mph with gusts to 85 mph increasing to 70 to 75 mph with gusts to 115 mph in the afternoon 65 to 75 mph with gusts to 115 mph 40 to 50 mph with gusts to 80 mph
Expected snowfall: up to 5 in. 10 to 22 in. 4 to 6 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.