THIS AVALANCHE FORECAST EXPIRED ON December 11, 2019 @ 7:00 am
Avalanche Forecast published on December 10, 2019 @ 7:00 am
Issued by Steve Reynaud - Tahoe National Forest

MODERATE avalanche danger will exist due to a combination of wind slab and storm slab avalanche problems.  Unusual storm slab conditions continue with buried surface hoar beneath the recent storm snow.  Human triggered avalanches are possible in specific areas today.

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: Wind Slab
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Increasing winds today will mean blowing snow and new wind slab formation.  Unstable wind slabs continued to exist in some areas yesterday and new ones will form on top of them today.  Plenty of soft snow remains on most ridgetop areas to be transported by the forecasted strong SW winds today.  Light snow flurries will add to the snow available for transport into tonight.

Look for active wind loading in the form of blowing snow and cornice formation.  Problematic wind slabs are expected in near and above treeline areas where winds can transport snow effectively. 

Avalanche Problem 2: Storm Slab
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Unusual storm slab conditions exist in our area.  The recent storm snow from Dec. 6-8 sits on top of a layer of buried surface hoar that has been found in many locations throughout the forecast region.  This weak layer is remaining reactive much longer than our typical storm slabs.  A boarder triggered avalanche yesterday resulted in a full burial that failed on this buried surface hoar layer.  Problematic storm slabs are 1-2’ deep, located on NW-N-NE-E aspects above 8000’, in open below treeline terrain, where this buried surface hoar layer exists.

While general snowpack stability may seem good in many areas, storm slab avalanches could still be human triggered.  Avalanches could have wide propagation, be remotely triggered, fail mid slope, and potentially show no other signs of instability in the area.  Look out for common trigger points, especially convex roll overs.  Avoid being connected to larger exposed avalanche slopes or complex terrain. 

recent observations
Submit Observations

* A boarder triggered avalanche resulted in a full burial in the Castle Peak area yesterday.  The avalanche occurred mid slope at 8300', was remotely triggered, and had wide propagation.  The weak layer was identified as buried surface hoar beneath Dec. 6-8 storm slab.

* A recent natural wind slab avalanche was seen on Red Lake Peak (Carson Pass area) yesterday.  Many signs of recent wind transport were observed with easy cracking and failing of wind features in wind loaded terrain.

* Previous natural avalanche activity was reported from the Castle Peak/Basin Peak area that had the characteristics of avalanches with a buried surface hoar weak layer.

Weather and CURRENT CONDITIONS
weather summary

High pressure will slowly exit our area today as a weak storm brings high clouds, increased winds, and the chance of a dusting of snow.  SW ridgetop winds could be gusting to 40-50mph by this afternoon and 50-60mph tonight.  Around 1'' of new snow is expected during the overnight hours.  SW winds continue into Wednesday with mostly unsettled weather and mild temperatures.

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 38 deg. F.
Max. temperature: 40 deg. F.
Average ridgetop wind direction: NE shifting to SW
Average ridgetop wind speed: 10 to 15 mph
Maximum ridgetop wind gust: 27 mph
New snowfall: 0 inches
Total snow depth: 45 to 55 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Cloudy. Slight chance of snow after midnight. Snow levels below 7000 feet. Chance of precipitation is 25%. Mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 10%.
Temperatures: 38 to 43. deg. F. 22 to 28. deg. F. 36 to 41. deg. F.
Mid Slope Winds: Light winds becoming southwest around 15 mph with gusts to 25 mph in the afternoon. Southwest 15 to 20 mph with gusts to 35 mph. Southwest around 15 mph. Gusts up to 25 mph increasing to 35 mph in the afternoon.
Expected snowfall: No accumulation. | SWE = none. 70% probability less than 1 inch. 30% probability of 1 to 2 inches. | SWE = less than 0.10 inch. No accumulation. | SWE = none.
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Mostly cloudy. Slight chance of snow after midnight. Snow levels below 7000 feet. Chance of precipitation is 25%. Mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 10%.
Temperatures: 35 to 40. deg. F. 20 to 26. deg. F. 34 to 39. deg. F.
Ridge Top Winds: Southwest around 15 mph increasing to 20 to 30 mph with gusts to 40 mph in the afternoon. Southwest 20 to 35 mph with gusts to 50 mph. Southwest 15 to 30 mph with gusts to 60 mph.
Expected snowfall: No accumulation. | SWE = none. 70% probability less than 1 inch. 30% probability of 1 to 2 inches. | SWE = less than 0.10 inch. 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