THIS AVALANCHE FORECAST EXPIRED ON December 21, 2020 @ 6:55 am
Avalanche Forecast published on December 20, 2020 @ 6:55 am
Issued by Brandon Schwartz - Tahoe National Forest

Unstable conditions are persisting, longer than what often occurs in this region. Trigging a large avalanche remains possible, especially near treeline and below treeline. Additionally, small unstable slabs of wind drifted snow may exist above treeline and near treeline. MODERATE avalanche danger exists at all elevations. This is not the time to try and outsmart the snowpack. Stick with mellow terrain for now, waiting patiently for the right set of conditions to move into bigger, steeper terrain at another time.

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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Instability associated with a persistent slab avalanche problem is just that - persistent. While snowpack data suggests that instability associated with this problem is decreasing, instability is still very much present and widespread. Continue to exercise caution. Conservative, lower angle terrain choices remain the way to go. Shaded sub 30 degree angle slopes still hold plenty of fun snow for recreation. Don't get frustrated with the conditions and push the limits. Act like a pro and work within the appropriate confines of the day. This is not the time to go big or to try and outsmart the snowpack.

This avalanche problem is widespread near treeline and below treeline and in isolated areas above treeline on W-NW-N-NE-E aspects. A slab of around 1 foot+ of recent new snow sits on top of a weak layer of sugary, faceted snow (Dec 11 PWL). Cracking, whumpfing (audible snowpack collapse), or snowpit tests can provide clues to the presence of instability. Sometimes triggering a large avalanche is the first and only clue to instability you get. This is not an easy avalanche problem to manage in avalanche terrain. Conversely, by limiting exposure to avalanche terrain by using only sub 30 degree angle slopes without steeper connected slopes above or to the side this becomes an easy avalanche problem to manage. The choice is yours.

Avalanche Problem 2: Wind Slab
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Recent SW to W ridgetop wind has drifted small amounts of snow above treeline and near treeline. Small unstable wind slabs could be encountered in these areas on NW-N-NE-E-SE aspects. Slopes below or adjacent to cornice features and/or pillows of wind drifted snow are the most suspect. Move around these areas with caution.

recent observations
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* Two potential persistent slab avalanches have been reported since Dec 14, but the weak layer in both instances is unverified. One avalanche occurred Dec 14 on the N side of Castle Peak on a NE aspect at 8,200-8,400' at size D2. The other avalanche was reported yesterday south of Carson Pass (exact occurrence day/time unknown) in small terrain somewhere between The Nipple and Blue Lakes Rd on an N to NE aspect at around 8,200'.

* Unstable snowpit test results and audible snowpack collapse (whumpfing) continue to occur daily on the Dec 11 persistent weak layer of faceted snow. Snowpit tests are showing increasing amounts of mixed clearly unstable vs non-propagating failure results. Collapses are reduced in frequency and do not propagate as far as compared to the start of this week.

* Small wind slabs were observed yesterday at and above treeline.

 Reported yesterday from south of Carson Pass. Unverified weak layer but this has the signature of a persistent slab avalanche. Shallow wind slab crown on looker's right half likely stepped down to deeper faceted snow on the left side. Long fractures in the snow on the far right side likely go down to faceted snow (Dec 11 PWL).

Weather and CURRENT CONDITIONS
weather summary

Air temperature inversion conditions are in place with above freezing air temperatures overnight on the peaks and well below freezing air temperatures on the mountain valley floors. These conditions are expected again tonight before increased winds on Monday night mix the atmosphere. Mostly sunny conditions are forecast for today and tomorrow. Light to moderate ridgetop wind speeds out of the West are expected for today. There is a slight chance of light snowfall over the far northern portion of the forecast area Monday night.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 36 to 40 deg. F.
Max. temperature: 40 to 44 deg. F.
Average ridgetop wind direction: W
Average ridgetop wind speed: 18 mph
Maximum ridgetop wind gust: 35 mph
New snowfall: 0 inches
Total snow depth: 24 to 31 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Sunday Sunday Night Monday
Weather: Sunny. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 0%. Clear. Snow levels 7000 feet decreasing to below 7000 feet after midnight. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 0%.
Temperatures: 44 to 49. deg. F. 25 to 33. deg. F. 42 to 47. deg. F.
Mid Slope Winds: Light winds. Light winds. Light winds.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. No accumulation. | SWE = none.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Sunny. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 0%. Clear. Snow levels 7000 feet. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 0%.
Temperatures: 41 to 47. deg. F. 25 to 31. deg. F. 39 to 44. deg. F.
Ridge Top Winds: West around 15 mph with gusts to 25 mph in the morning becoming light. Light winds becoming southwest around 15 mph after midnight. West 15 to 20 mph. Gusts up to 25 mph increasing to 45 mph in the afternoon.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. No accumulation. | SWE = none.
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