THIS AVALANCHE FORECAST EXPIRED ON January 8, 2019 @ 6:58 am
Avalanche Forecast published on January 7, 2019 @ 6:58 am
Issued by Steve Reynaud - Tahoe National Forest

CONSIDERABLE avalanche danger exists at all elevations throughout the forecast region due to wind slab and storm slab avalanche problems.  Dangerous avalanche conditions exist with the potential for large destructive avalanches today. 

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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Gale force S/SW winds throughout the last 2 days of this storm cycle have created large fragile wind slabs on NW-N-NE-E-SE aspects in near treeline and above treeline areas.  Some of these wind slabs sit on top of old weak snow layers that could allow remote triggering with wide propagation.  A warming trend overnight has created an "upside down" snowpack in some areas with heavier snow on top of less dense snow.  These wind slabs could involve multiple feet of snow and have severe consequences.

Cautious route finding, decision making, and terrain management are critical today.  Large destructive avalanches are likely.  Look for blowing snow, cornice formation, and wind pillows to help identify where wind slabs exist. 

 

Avalanche Problem 2: Storm Slab
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Storm slab avalanches will be likely today on all aspects in near and below treeline terrain.  2 to 4'+ of new snow has fallen in the last 2 days.  In many areas of the forecast region, this new snow sits on top of old weak faceted snow layers.  A warming trend overnight has made the recent storm snow "upside down" with heavier denser snow on top of less dense snow.  Large destructive avalanches that behave like persistent slab avalanches could occur today with remote triggering and wide propagation possible.  

Look for cracking around skis or whumpfing sounds to indicate storm slab instabilities.  If these signs exist, move to different aspects and/or low angle terrain well below 30 degrees with no overhead hazard.

  

Forecast discussion

Most avalanche fatalities and accidents occur under the Considerable avalanche danger rating.  We have just received up to 4' of new snow with over 100mph winds within the last 48 hours.  Winds and snow are expected to wind down this morning.  Do not be surprised to see large natural avalanches out in the backcountry today that occurred during this storm.  On top of the wind slab and storm slab avalanche problems, uncertainty exist as to the strength and reactivity of the old weak faceted snow now buried under this storm snow.  Conservative decision making today is warranted.   

recent observations
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*  Observations from Andesite Peak (Donner Summit area) showed increasing instabilities throughout the day.  Several small skier triggered wind slab avalanches were observed along with storm slab instabilities that increased with the additional new snow.  Snowpack tests targeting the old weak faceted snow showed easy failure along with several whumpfing sounds throughout the day.

*  Tamarack Peak (Mt. Rose area) showed wind slabs failing easily and building throughout the day.  Storm slab instability was also observed at the new snow old snow interface.

*  Observation from Poison Peak (Bear Valley area) also showed weak faceted old snow layers below the new storm snow.

Weather and CURRENT CONDITIONS
weather summary

Wind and snow showers will diminish this morning as this storm system moves east.  Impressive snow totals are in the 2 to 4' range over the Sierra Crest, with up to 2' of that in the last 24 hours.  SW gale force winds were blowing in the 50 to 90mph range with gusts just shy of 150mph overnight.  Temperatures have warmed overnight with rain up to potentially 7000' in some locations.  We get a short break this afternoon and Tuesday before another storm impacts our area on Tuesday night into Wednesday.  This storm will not be as impressive as what we just seen, but still could put down 1' along the Sierra Crest.  The weather pattern continues to look active through the weekend.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 25 to 30 deg. F.
Max. temperature: 30 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 50 to 85 mph
Maximum ridgetop wind gust: 148 mph
New snowfall: 12 to 21 inches
Total snow depth: 51 to 56 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. Snow levels below 7000 feet. Chance of precipitation is 55%. Cloudy. Slight chance of showers in the evening. Slight chance of snow showers after midnight. Snow levels 7000 feet. Chance of precipitation is 10%. Cloudy. Slight chance of showers through the day. Snow levels 7500 feet. Chance of precipitation is 25%.
Temperatures: 32 to 37. deg. F. 26 to 32. deg. F. 36 to 41. deg. F.
Mid Slope Winds: Southwest 20 to 35 mph. Gusts up to 65 mph. South 10 to 15 mph with gusts to 35 mph. South 15 to 20 mph. Gusts up to 25 mph increasing to 40 mph in the afternoon.
Expected snowfall: 80% probability of 1 to 2 inches. 20% probability of 2 to 4 inches. | SWE = up to 0.20 inch. No accumulation. | SWE = less than 0.10 inch. No accumulation. | SWE = trace amounts.
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Mostly cloudy. Chance of snow showers. Snow levels below 7000 feet. Chance of precipitation is 55%. Cloudy. Slight chance of snow showers in the evening. Snow levels 7000 feet. Chance of precipitation is 15%. Mostly cloudy. Slight chance of snow showers in the afternoon. Snow levels 7500 feet. Chance of precipitation is 25%.
Temperatures: 28 to 33. deg. F. 24 to 29. deg. F. 33 to 38. deg. F.
Ridge Top Winds: Southwest 35 to 55 mph. Gusts up to 95 mph decreasing to 70 mph in the afternoon. Southwest 25 to 35 mph with gusts to 70 mph shifting to the south 15 to 30 mph with gusts to 50 mph after midnight. South 15 to 30 mph with gusts to 60 mph increasing to 30 to 45 mph with gusts to 75 mph in the afternoon.
Expected snowfall: 80% probability of 1 to 2 inches. 20% probability of 2 to 4 inches. | SWE = up to 0.20 inch. No accumulation. | SWE = less than 0.10 inch. No accumulation. | SWE = trace amounts.
Disclaimer

This avalanche forecast is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This forecast 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 forecast applies only to backcountry areas outside established ski area boundaries. This forecast describes general avalanche conditions and local variations always occur. This forecast expires 24 hours after the posted time unless otherwise noted. The information in this forecast is provided by the USDA Forest Service who is solely responsible for its content.

For a recorded version of the avalanche forecast call (530) 587-3558 x258