THIS AVALANCHE ADVISORY EXPIRED ON January 7, 2018 @ 6:59 am
Avalanche Advisory published on January 6, 2018 @ 6:59 am
Issued by Brandon Schwartz - Tahoe National Forest

CONSIDERABLE avalanche danger exists at all elevations due to a combination of loose wet, wind slab, and persistent slab avalanche problems. Intentionally choose terrain, evaluate slope aspect(s) for the presence or absence of avalanche problems, identify likely areas of triggering, and evaluate avalanche consequences in terms of potential size and down slope hazards. Determine how much you really know based on actual data vs what is a guess or pre-bias. If in doubt, make a more conservative choice.

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: Loose Wet
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Loose wet avalanche activity was occurred the past two days. Rain and wet snow will keep this avalanche problem ongoing today. In some areas below 8,500' the upper snowpack may be soaked. Snow covered NW-N-NE aspects at any elevation are the likely location for this avalanche problem to occur. Loose wet avalanches are possible in isolated areas on all other aspects as well. Avalanche size up to D2 is possible.

Avoid steep terrain in areas where natural or human triggered roller ball activity is occurring. Even small loose wet avalanches can have significant consequences if a person is pushed into a rock or tree, over a cliff, or into a terrain trap.

Avalanche Problem 2: Wind Slab
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New wind slabs will have formed overnight above 8,500' in near treeline and above treeline terrain on NW-N-NE-E aspects. Isolated wind slabs may exist on cross loaded SE aspects as well. Avalanche size could reach D2. Look for and avoid areas of recently drifted snow, especially along ridgelines were signs of recent cornice and wind pillow formations exist.

Avalanche Problem 3: Persistent Slab
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Significant rain and wet snow have added more load to areas of slab over weak faceted snow on NW-N-NE aspects both above and below treeline. Field observations from Dec 25th through yesterday have regularly indicated isolated areas of persistent slab instability. Increasing moisture in the upper snowpack from rain and wet snow have improved the strength of the facet layer in some areas. In areas where overlying slab is thicker as well as in upper elevation areas, the facets have remained drier, looser (more sugary), and weaker. Avalanches failing within the old snow up to size D2 are possible.

Near and below treeline, quick hand pits remain effective for identifying slab over weak, loose grain (sugary) faceted snow but you may need to dig fairly deep above 8,500'. Keep in mind that this problem exists in isolated areas so investigate the snowpack structure frequently as you cover terrain. This problem may exist only in the mid to lower portion of avalanche start zones, not at the very top where past NE wind scouring occurred. Dig in the right places.

Avoid steeper slopes in areas where snow surface cracking, whumpfing, and/or unstable snowpit test results are occurring. Keep this avalanche problem at the forefront of decision making even though it is third on the list.

recent observations

* More loose wet avalanche activity was observed yesterday. This time it was on N to NE aspects of Red Lake Peak above Crater Lake in the 8,800' to 9,300' elevation range.

* The recent rain, wet snow, and high humidity has added significant moisture to areas that held faceted snow on the surface with no overlying slab.

* Where faceted snow exists under a slab, the facets remained dry and reactive in snowpit tests as of Friday afternoon.

* NW-N-NE aspects above 8,000' in the Mt. Rose area and along the Sierra Crest north of Emerald Bay hold the best snow coverage at 2 to 3+ feet. Overall less snow cover exists south of Emerald Bay. Areas of decent coverage exists above 8,500' on NW-N-NE aspects in the Carson Pass area.  Coverage decreases on all other aspects. Large areas of bare ground exist on the vast majority of southerly aspects at all elevations.

Weather and CURRENT CONDITIONS
weather summary

The storm system currently moving through the forecast area has deposited 1.4 to 1.9 inches of rain over the northern half of the forecast area and 0.5 to 1.0 inch of rain over the southern half of the forecast area. Snow level has held around 8,000' to 8,500' overnight. New snow amounts between 8,500' and 8,800' range from 3 to 9 inches. Greater amounts may have accumulated over the highest elevations. Precipitation is expected to taper off mid to late morning with the possibility of lingering showers this afternoon. Snow level is expected to fall to around 7,000' later this morning. Strong SW ridgetop winds will gradually decrease to moderate speed later today and tonight. A short period of high pressure will build in Sunday before a powerful storm affects the forecast area Monday/Tuesday.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 31 to 41 deg. F.
Max. temperature in the last 24 hours: 33 to 41 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 39 mph
Maximum wind gust in the last 24 hours: 77 mph
New snowfall in the last 24 hours: 3 to 9 inches
Total snow depth: 19 to 34 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy skies with rain and snow in the morning. A chance of rain and snow in the afternoon. Snow level 8,000' lowering to 7,000'. Partly cloudy skies. Sunny skies.
Temperatures: 39 to 44 deg. F. 28 to 33 deg. F. 46 to 51 deg. F.
Wind Direction: SW SW SW
Wind Speed: 15 to 25 mph. Gusts up to 50 mph decreasing to 40 mph in the afternoon. 10 to 15 mph with gusts to 25 mph in the evening, becoming light. Light winds
Expected snowfall: Likely up to 1 in. | Small chance 2 to 3 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy skies with rain and snow in the morning. A chance of snow in the afternoon. Snow level 8,000'. Partly cloudy skies. Sunny skies.
Temperatures: 35 to 40 deg. F. 28 to 33 deg. F. 42 to 47 deg. F.
Wind Direction: SW SW SW
Wind Speed: 30 to 45 mph with gusts to 85 mph, decreasing to 25 to 35 mph with gusts to 65 mph in the afternoon. 20 to 30 mph. Gusts to 65 mph decreasing to 45 mph after midnight. 10 to 15 mph. Gusts up to 30 mph increasing to 40 mph in the afternoon.
Expected snowfall: Likely 1 to 3 in. | Small chance 4 to 6 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