THIS AVALANCHE ADVISORY EXPIRED ON March 28, 2017 @ 7:00 am
Avalanche Advisory published on March 27, 2017 @ 7:00 am
Issued by Steve Reynaud - Tahoe National Forest

Considerable avalanche danger exists due to wind slab, storm slab, and loose wet avalanche problems.  Wind slabs will be likely in near treeline and above treeline terrain.  Storm slabs will be possible in near treeline and below treeline terrain.  Loose wet avalanches will be possible at all elevations.  Natural triggered avalanches are possible and human triggered avalanches are likely.  Areas north of Tahoe City along the Sierra Crest received the most snow overnight with more avalanche concerns. 

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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Strong to gale force S winds have created wind slabs on W-NW-N-NE-E aspects in near treeline and above treeline terrain.  As winds shift towards the W today, wind slabs will also be possible on SE-S aspects in near treeline and above treeline areas.  If rapid warming occurs today due to solar radiation, these wind slabs could be further weakened and more prone to avalanching.  These wind slabs are expected to be larger along the Sierra Crest North of Tahoe City.

Look for blowing snow, cornice formation, wind pillows, and evidence of previous wind loading.  Avoid steep wind loaded slopes and area below cornices.

Avalanche Problem 2: Loose Wet
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Loose wet avalanche activity will be possible on E-SE-S-SW-W aspects at all elevations and on NW-N-NE aspects in below treeline areas.  Depending on cloud cover in your area, rapid warming could occur starting mid morning due to solar radiation.  The new storm snow now sits on a thin firm sun crust on most aspects and elevations except North.  As this new snow warms up it will have an efficient bed surface to slide on.

If the snow surface becomes wet, it is time to switch aspects to colder snow or leave the area.  Loose wet avalanches large enough to injure or bury a backcountry user are possible.  Look for evidence of roller balls or loose wet avalanches to determine what aspects and elevations are experiencing rapid warming .  Terrain traps, such as gullies, can magnify the consequences of even a small loose wet avalanche.   

Avalanche Problem 3: Storm Slab
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Storm slabs will be possible on all aspects in near treeline and below treeline terrain.  These storm slabs will be limited to areas N of Tahoe City along the Sierra Crest where the most snow fell overnight.  Rapid warming from solar radiation could make these storm slabs more prone to failure.  Look for cracking around skis or any signs of cohesion within the new storm snow.  Avoid slopes that show signs of unstable snow.

recent observations

Observations were made and received from Elephants Hump (Carson Pass area) and Negro Canyon (Donner Summit area).  Strong SW winds were moving light amounts of snow at both locations.  Wind slabs were small and not found to be reactive at either area.  Very light snow showers were on and off on Carson Pass with long periods of partly sunny conditions.  A variety of sun crusts and melt freeze crusts exist out there with different levels of supportability.  At lower elevations on Donner Summit, supportable sun crusts provided good travel conditions on E-S aspects.   

Weather and CURRENT CONDITIONS
weather summary

The current storm will continue to bring precipitation to our area through this morning.  As of 6am, 2 to 10'' of new snow has fallen above 7000' with areas along the Sierra Crest North of Tahoe City receiving the most snow.  A Northwest flow will develop by midday as the cold front passes with cold and dry air.  A warming trend will start on Tuesday with a NE flow.  By Wednesday, temperatures could be pushing into the 50's at lake level with light winds.  Then another storm is possible on Thursday.  After Thursday, the weather models struggle to find a solution but it appears that unsettled weather continues.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 20 to 27 deg. F.
Max. temperature in the last 24 hours: 39 deg. F.
Average wind direction during the last 24 hours: S
Average wind speed during the last 24 hours: 30 to 50 mph
Maximum wind gust in the last 24 hours: 77 mph
New snowfall in the last 24 hours: 2 to 10 inches
Total snow depth: 117 to 178 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Monday Monday Night Tuesday
Weather: Mostly cloudy. Chance of snow showers in the morning. Partly cloudy then becoming clear. Sunny
Temperatures: 34 to 39 deg. F. 21 to 27 deg. F. 44 to 49 deg. F.
Wind Direction: W N
Wind Speed: 10 to 15mph. Gusts to 35mph decreasing to 25mph in the afternoon. 10 to 15mph with gusts to 35mph. Light winds.
Expected snowfall: Up to 1 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Mostly cloudy then becoming partly cloudy. Slight chance of snow showers. Partly cloudy then becoming clear. Sunny
Temperatures: 29 to 35 deg. F. 20 to 25 deg. F. 40 to 46 deg. F.
Wind Direction: W N NE
Wind Speed: 15 to 25mph. Gusts to 65mph decreasing to 40mph in the afternoon. 15 to 25mph. Gusts to 45 increasing to 60mph after midnight. 20 to 30mph. Gusts to 70 decreasing to 55mph in the afternoon.
Expected snowfall: Up to 1 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