THIS AVALANCHE FORECAST EXPIRED ON January 16, 2020 @ 7:00 am
Avalanche Forecast published on January 15, 2020 @ 7:00 am
Issued by Steve Reynaud - Tahoe National Forest

Human triggered wind slab avalanches will be possible today.  MODERATE avalanche danger will exist in near and above treeline areas due to wind slabs with LOW avalanche danger in below treeline terrain.  Avalanche danger is expected to increase dramatically tomorrow.

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.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    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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    Certain
    Very Likely
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    Very Large
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Gale force SW winds yesterday transported large amounts of new and existing snow.  Winds have decreased somewhat, but are still in the moderate to strong range and capable of moving additional snow.  Winds will pick back up to gale force this afternoon and through the night ahead of our next storm.  Lingering wind slabs will be possible today in near and above treeline areas.  Wind slab avalanches that are multiple feet deep could be human triggered today.  

Look for active wind loading or signs of previous wind loading.  Wind scoured terrain down to firm crusts exist on most all exposed ridges and high points.  Recently deposited wind pillows are below ridgelines and extend far downslope.  Manage terrain and avoid exposure below large cornices and steep wind loaded areas.   

Forecast discussion

A large winter storm is forecasted to hit the forecast area Thursday morning.  We have been monitoring the Jan 4 rain crust and weak faceted snow that has formed above and below this crust.  It has been found on NW-N-NE-E aspects in below treeline and near treeline areas throughout the forecast region.  Some signs are showing that these layers could fail under additional load tomorrow as a large storm impacts our area.  Failure of this layer could make for larger and wider storm slab avalanches.  These storm slab avalanches could be remotely triggered, occur mid slope or in below treeline terrain, and potentially be much larger than anticipated.  These avalanches could exist outside of our standard start zones that are not associated with our "normal" avalanche terrain. 

recent observations
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Observations were received yesterday from Silver Peak (Pole Creek area), Rubicon Peak (West Shore area), and Tamarack Peak (Mt Rose area).  Strong to gale force SW winds with intense active wind loading was experienced at all locations.  Small cracking in wind loaded terrain occurred at all locations, but limited other signs of instabilities existed.  Snowpack tests along with informal observations showed some of these newly forming wind slabs to be stubborn or unreactive to triggering.

The Jan 4 rain crust with weak faceted snow was found on Rubicon Peak and Silver Peak.  On Silver, localized cracking occurred down to the Jan 4 rain crust with the addition of 3'' of new storm snow.  This was thought to be an indication of the weakness of this faceted snow/rain crust.  With a larger load forecasted for Thursday, there is potential that this weak layer could fail.

 

Photo: Cracking through recent storm snow down to the Jan 4 rain crust in wind protected below treeline areas.  Silver Peak.

Weather and CURRENT CONDITIONS
weather summary

There will be a break today in the weather with this morning being mostly clear.  Increasing winds and clouds will ramp up this afternoon in front of our next storm system forecasted for Thursday morning.  Increasing SW winds will reach strong to gale force later today and through the night.  The Thursday storm is still on schedule with 1 to 2' of new snow forecasted along the Sierra Crest with gale force winds.  The weather will clear out on Friday with cold temperatures.  The weekend looks mostly clear with a slight chance of snow on Saturday.  After a quiet weather weekend, active weather could return early next week.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 10 to 22 deg. F.
Max. temperature: 18 to 26 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 25 to 35 mph
Maximum ridgetop wind gust: 115 mph
New snowfall: 1 to 2 inches
Total snow depth: 41 to 48 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Wednesday Wednesday Night Thursday
Weather: Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%. Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 10%. Cloudy. Snow likely in the morning, then snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 100%.
Temperatures: 34 to 40. deg. F. 22 to 27. deg. F. 28 to 33. deg. F.
Mid Slope Winds: Southwest around 15 mph. Gusts up to 35 mph in the afternoon. Southwest 15 to 30 mph. Gusts up to 50 mph increasing to 70 mph after midnight. South 20 to 35 mph with gusts to 75 mph.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. 80% probability of 7 to 12 inches. 20% probability of 12 to 15. | SWE = up to 0.85 inch.
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%. Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%. Cloudy. Chance of snow in the morning, then snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 100%.
Temperatures: 30 to 36. deg. F. 19 to 24. deg. F. 24 to 30. deg. F.
Ridge Top Winds: Southwest 20 to 35 mph with gusts to 70 mph. Southwest 30 to 50 mph with gusts to 80 mph. South 35 to 55 mph with gusts to 85 mph.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. 80% probability of 9 to 15 inches. 20% probability of 15 to 18. | SWE = 0.60-1.10 inches.
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