THIS AVALANCHE ADVISORY EXPIRED ON March 19, 2016 @ 7:00 am
Avalanche Advisory published on March 18, 2016 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE avalanche danger will form on sun exposed E-SE-S-SW-W aspects steeper than 35 degrees at all elevations as daytime warming creates wet snow on these aspects. Loose wet snow avalanches including roller balls, pinwheels, and point releases will be possible today. While cornice failure has become unlikely, it is not impossible and today's warming could also weaken some of the large overhanging cornices that exist on the NW-N-NE-E-SE aspects along exposed ridgelines on isolated terrain features as well. 

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 remained above freezing in some areas last night, the clear skies allowed the snowpack to radiate heat out into the night sky and refreeze. This refreeze will quickly melt away as the strong March sun and warm daytime temperatures heat up the snowpack. The snowpack has not been through enough melt freeze cycles to form good drainage channels to deal with the free water that forms due to the warming or to transition to corn snow conditions. Once the refreeze melts, loose wet snow avalanches in the form of roller balls, pinwheels, and point releases will become possible again today. The sun exposed E-SE-S-SW-W aspects hold the best potential for loose wet avalanches. Most of the loose wet snow instabilities should remain small, but some of them could entrain enough snow to cause problems for backcountry travelers. 

Use clues like sinking into boot-top deep wet snow and smaller surface wet snow instabilities like roller balls and pinwheels to indicate that enough wet snow exists for problematic loose wet avalanches. These signs indicate that the time has come to move to more frozen slopes, move to less steep slopes, and/or switch activities for the afternoon. 

Avalanche Problem 2: Cornice
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Many of the the large cornices that formed during the recent storm failed during or just after the storm and some have broken under the weight of a person or snowmobile since the storm. However, many large overhanging cornices still remain perched above wind loaded slopes along exposed ridgelines. While these cornices have become more difficult to break, today's warming will weaken these cornices, and the potential exists for some of them to break on isolated terrain features where they are most overhung and least supported. A great deal of uncertainty exists concerning the strength of these cornices and how far back they may break.

Identify where cornices exist and stay well back from their edges. Often determining how much a cornice overhangs a slope is difficult, and even when the overhang is visible, they can break behind that point. Giving these large cornices more space than seems necessary represents a wise choice.

recent observations

Yesterday observations from Donner Peak, Mt. Judah (Donner Summit area), Jakes Peak, and Stevens Peak (Carson Pass area) all showed wet snow forming on the sun exposed aspects by mid morning. Human triggered roller balls and pinwheels occurred on Jakes Peak, Mt. Judah, and on Stevens Peak. On Donner Peak observers noted a glide crack had formed as the snow slowly slid down one of wet granite slabs. Also some natural loose wet activity started to occur on low elevation east facing slopes by 10 am. The north facing aspects also held wet snow and breakable crusts below 7800 ft. on Mt. Judah and below 8500 ft. on Stevens Peak. Above these elevations the north facing aspects held a mix of firm wind packed surfaces on exposed slopes and shallow cold soft snow on sheltered slopes. Large cornices still loomed over many slopes in the Mt. Judah area, along the Sierra Crest south of Mt. Judah, and in the Desolation Wilderness around Jakes Peak. 

Weather and CURRENT CONDITIONS
weather summary

High pressure over the region will keep the weather warm and dry and sunny through tomorrow. Daytime highs should climb into the low to mid 50's above 7000 ft. today with overnight lows in the 30's tonight. The calm winds and clear skies should give way to increased southwest winds and some partly cloudy skies tomorrow afternoon as the ridge pushes eastward and another storm begins to approach the area. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 36 to 42 deg. F.
Max. temperature in the last 24 hours: 48 to 54 deg. F.
Average wind direction during the last 24 hours: Southwest and northeast
Average wind speed during the last 24 hours: 5 to 10 mph
Maximum wind gust in the last 24 hours: 22 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 80 to 117 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Sunny Clear Sunny becoming partly cloudy
Temperatures: 49 to 56 deg. F. 32 to 37 deg. F. 48 to 55 deg. F.
Wind Direction: Variable Variable becoming southwest after midnight Southwest
Wind Speed: Light 10 mph 10 to 15 mph with gusts to 25 mph increasing to 35 mph in the afternoon
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Sunny Clear Sunny becoming partly cloudy
Temperatures: 43 to 53 deg. F. 30 to 36 deg. F. 40 to 48 deg. F.
Wind Direction: West Southwest Southwest
Wind Speed: 5 to 15 mph 15 to 20 mph with gusts to 30 mph 15 to 25 mph with gusts to 35 mph increasing to 45 mph in the afternoon
Expected snowfall: 0 in. 0 in. 0 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