THIS AVALANCHE FORECAST EXPIRED ON December 31, 2020 @ 6:59 am
Avalanche Forecast published on December 30, 2020 @ 6:59 am
Issued by Steve Reynaud - Tahoe National Forest

Persistent slab and wind slab avalanche problems continue for our area.  It remains possible to trigger a large avalanche in our forecast region due to our poor snowpack structure.  MODERATE avalanche danger exists at all elevations.  Conservative terrain choices are recommended when traveling in the backcountry.

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: Persistent Slab
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The Dec. 11 persistent weak layer remains buried in our snowpack and is widespread in near and below treeline areas and more isolated in above treeline areas.  The lower part of our snowpack structure remains weak with this faceted layer buried around 1.5 to 2.5 feet deep below the snow surface.  The likelihood of triggering an avalanche has decreased and we have had no known avalanches occur in the last 2 days.  With that said, triggering a large avalanche remains possible as this weak layer could take a long time to gain strength.  Unfortunately, the weak layer will gain strength at different rates at different locations- with whumpfing, cracking, and unstable snowpack test results reported in some areas with few or no signs of instabilities reported from other areas.  The Dec 11 PWL has already caused large avalanches, with wide propagation, and remote triggering-and that will continue to remain possible.

Conservative terrain choices remain the best way for managing a persistent slab avalanche problem.  Conditions are very good on low angle sub 30 degree terrain and remain a great way to avoid this avalanche problem.  Be aware of connected terrain above, below, or to the side of you or your group that could be remotely triggered.  Persistent slabs are notorious for behaving in unpredictable ways.  Wide propagation, large avalanches, mid slope avalanches, and avalanches on slopes that already have tracks could occur.              

Avalanche Problem 2: Wind Slab
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NE winds on Monday night transported snow onto SE-S-SW-W-NW aspects in near and above treeline areas.  Winds will shift to the SW/W and increase in speed throughout the day and into tonight ahead of a fast moving small storm.  Up to 6'' of new snow is possible late tonight into Thursday morning.  Snow transport along with new small wind slabs are expected to build throughout the day today on NW-N-NE-E-SE aspects in near and above treeline areas.

recent observations
Submit Observations

* Whumpfing, cracking, and some unstable snowpack test results continued on Elephants Hump (Carson Pass area) yesterday.  

* Slightly buried surface hoar, 1-2'' below the surface, continues to be reported in new areas of the forecast region along with widespread newly developed surface hoar.

* A wide propagating avalanche was reported yesterday from Webber Peak (Little Truckee Summit area).  Trigger is unknown as well as when it occurred.  Some evidence points to the Sat/Sun timeframe post Dec 25 storm.

  

Weather and CURRENT CONDITIONS
weather summary

NE winds will shift to the SW/W this morning and increase in speed ahead of a fast moving storm tonight into Thursday morning that is forecasted to bring 3 to 6'' of snow to the Sierra Crest.  SW winds this afternoon and evening could gust upwards of 100mph over the higher peaks.  After the storm exits our area on Thursday afternoon, gusty NE winds will develop into Friday.  The forecast still looks favorable for a string of pacific storms to enter our area the first week of 2021.  The first storm is expected on Saturday evening with a storm possible every 1-2 days through the first week of January.  

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 22 to 30 deg. F.
Max. temperature: 26 to 30 deg. F.
Average ridgetop wind direction: NE shifting to W
Average ridgetop wind speed: 20 to 30 mph
Maximum ridgetop wind gust: 55 mph
New snowfall: 0 inches
Total snow depth: 30 to 34 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Mostly cloudy. Chance of snow in the evening, then snow after midnight. Snow levels below 7000 feet. Chance of precipitation is 100%. Mostly cloudy then becoming partly cloudy. Chance of snow in the morning. Snow levels below 7000 feet. Chance of precipitation is 25%.
Temperatures: 35 to 40. deg. F. 19 to 25. deg. F. 28 to 33. deg. F.
Mid Slope Winds: Light winds. Southwest 15 to 20 mph with gusts to 40 mph. Northwest around 15 mph with gusts to 30 mph in the morning becoming light.
Expected snowfall: No accumulation. | SWE = none. 80% probability of 2 to 4 inches. 20% probability of 3 to 6 inches. | SWE = 0.15-0.25 inch. Up to 1 inch. | SWE = less than 0.10 inch.
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Mostly cloudy. Slight chance of snow in the evening, then snow after midnight. Snow levels below 7000 feet. Chance of precipitation is 100%. Mostly cloudy then becoming partly cloudy. Chance of snow in the morning. Snow levels below 7000 feet. Chance of precipitation is 25%.
Temperatures: 31 to 36. deg. F. 17 to 22. deg. F. 24 to 29. deg. F.
Ridge Top Winds: West 15 to 30 mph. Gusts up to 50 mph Southwest 30 to 50 mph with gusts to 90 mph. Northwest 25 to 35 mph with gusts to 75 mph shifting to the northeast 15 to 30 mph with gusts to 55 mph in the afternoon.
Expected snowfall: No accumulation. | SWE = none. 70% probability of 2 to 5 inches. 30% probability of 3 to 6 inches. | SWE = up to 0.30 inch. Up to 1 inch. | SWE = less than 0.10 inch.
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