THIS AVALANCHE ADVISORY EXPIRED ON November 28, 2016 @ 6:51 am
Avalanche Advisory published on November 27, 2016 @ 6:51 am
Issued by Steve Reynaud - Tahoe National Forest

Considerable avalanche danger exists today due to wind slabs and persistent slabsWind slabs will exist on NW-N-NE-E-SE-S aspects in near treeline terrain and above treeline terrain.  Persistent slabs will exist on North aspects where previous old snow existed from late October and early November.  Dangerous avalanche conditions exist.  Careful snowpack evaluation, cautious route finding, and conservative decision making is essential.

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.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Winds overnight during most of the snowfall were from the SW in the moderate to strong range with some locations gusting much higher.  Wind slabs could have developed on NW-N-NE-E-SE aspects overnight.  As winds shift towards the W and then eventually to the NW throughout the day, wind slabs will continue to grow and may develop on SE-S aspects near and above treeline as well.  Most wind slab problems today will be on slopes 35 degrees and steeper.  Slopes with previous snow with some or all anchors covered up will be the most susceptible to wind slab formation.

Look for areas of blowing snow, cornice formation, and wind pillows.  Any cracking around skis in wind loaded terrain will be an indication that wind slabs have or are developing.  Even a small avalanche has great consequences with our early season snowpack.

Avalanche Problem 2: Persistent Slab
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Snow that fell in late October and early November has become faceted and weak.  These conditions exist on North aspects along the Sierra Crest north of Tahoe City above 8300' and in the Mt. Rose area above 9000'.  Snowpack tests in the Castle Peak area and the Mt. Rose area indicate that this persistent weak layer could propagate if triggered.  With the load of additional snow last night, these persistent slabs may become easier to trigger.  This problem could exist on slopes 30 degrees and steeper.

These persistent slabs exist in exactly the same area with the most snow for recreation.  Persistent slabs can be remotely triggered, do not give reliable information with informal observations, and existing tracks do not indicate stability.  Digging in the snow may be required to see if this problem exists in your area on your specific slope.  Avoiding North aspects above 30 degrees is another strategy to deal with this persistent weak layer

advisory discussion

The most usable snowpack within the forecast area exists along the northern portion of the Sierra Crest. Areas above 7,000' and north of Tahoe City have sufficient amounts of supportable snow for quality over snow travel (2 to 4 feet). Along the Sierra Crest south of Tahoe City, snowpack depths decrease dramatically, even at the highest elevations.  The Mount Rose area in the NE portion of the forecast area has decent snowcover (~2-3 feet) in areas that have held snow/ice since mid Oct. This is generally N aspects above 9,300'. Below 9,300' on N aspects or on all other aspects in the Mount Rose area, over snow travel is possible, but impact with rocks is likely with snow depths around 1-2 feet.

Due to the wide variances in snowcover between the northern and southern portions of the forecast area, this advisory is heavily biased towards the northern areas where the snowpack is more usable for over snow travel.

The avalanche center is still working on a limited number of observations so please submit observations through the "submit observations" buttons found throughout this website.

recent observations

Yesterday's observations on Tamarack Peak indicated that faceting has continued within the old snow from late October/early November.  Snowpack tests were mixed at many locations throughout the day.  The weak faceted layer was observed at all data gathering areas on North aspects above 9300' with more advanced faceting occurring above 9500'.  There was up to 1' of light unconsolidated snow on top of the weak layer.

Active wind transport was observed throughout the day with very little to no wind slab development seen.

Weather and CURRENT CONDITIONS
weather summary

We received 8 to 16'' of new snow overnight with isolated snow showers expected throughout this morning.  Moderate to strong SW winds overnight will switch to the W and eventually to the NW today.  West winds will be 25 to 40mph and gusting up to 90mph above 8000' today before switching to NW and decreasing to 15 to 25mph with gusts to 50mph in the afternoon.  Much colder air settles throughout our forecast area throughout the week with the possibility of light snow showers.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 16 to 19 deg. F.
Max. temperature in the last 24 hours: 29 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 30 to 50 mph
Maximum wind gust in the last 24 hours: 98 mph
New snowfall in the last 24 hours: 8 to 16 inches
Total snow depth: 14 to 28 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Sunday Sunday Night Monday
Weather: Cloudy then becoming partly cloudy. Snow in the morning then isolated snow showers in the afternoon. Cloudy. Slight chance of snow in the evening. Cloudy then becoming mostly cloudy. Chance of snow in the morning then slight chance in the afternoon.
Temperatures: 25 to 30 deg. F. 22 to 27 deg. F. 30 to 35 deg. F.
Wind Direction: NW W W
Wind Speed: 15 to 25mph. Gusts up to 45 decreasing to 35 in the afternoon. 10 to 20 with gusts to 30mph. Increasing to 15 to 25 with gusts to 50mph. 20 to 30mph with gusts to 60mph, decreasing to 15 to 20 with gusts to 40mph in the afternoon.
Expected snowfall: 1 to 4 in. Up to 1 in. Up to 1 in.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Cloudy, then becoming partly cloudy. Snow in the morning then isolated snow in the afternoon. Cloudy chance of snow after midnight. Cloudy then becoming mostly cloudy. Chance of snow in the morning then slight chance of snow in the afternoon.
Temperatures: 22 to 27 deg. F. 20 to 25 deg. F. 27 to 32 deg. F.
Wind Direction: W becoming NW NW becoming W W
Wind Speed: W 25 to 40 with gusts to 90mph becoming NW 15 to 25mph with gusts to 50mph in the afternoon. NW 15 to 25mph with gusts to 50mph becoming W 30 to 40mph gusting to 90mph after midnight. 40 to 60mph with gusts to 105mph decreasing to 30 to 40mph with gusts to 75mph in the afternoon.
Expected snowfall: 1 to 4 in. Up to 1 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