THIS AVALANCHE ADVISORY EXPIRED ON January 21, 2016 @ 6:54 am
Avalanche Advisory published on January 20, 2016 @ 6:54 am
Issued by Steve Reynaud - Tahoe National Forest

Moderate avalanche danger exists on NW-N-NE-E-SE aspects, on slopes steeper than 32 degrees, at all elevations, due to wind slabs and persistent slabs.  On S-SW-W aspects at all elevations, low avalanche danger exists.  Human triggered avalanches are possible today.  Evaluate snow and terrain carefully, identify features of concern. 

2. Moderate

?

Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

?

Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

?

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
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Sensitive and reactive wind slabs formed yesterday in near and above treeline terrain throughout the forecast area.  These winds slabs were 8'' to 2' in size and were failing on a density change within the new storm snow.  These wind slab avalanches were noted in several areas to have wide propagation and very poor bonding to the snow below and could be sensitive throughout today.

This problem exists in near and above treeline terrain on NW-N-NE-E and potentially SE aspects.  Look for evidence of previous blowing snow, cornice formation, wind pillows, and snow surface scouring to help identify where wind slabs exist. 

Avalanche Problem 2: Persistent Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Persistent weak layers in the form of buried surface hoar exist throughout the forecast region in some areas on N-NE-E aspects near and below treeline and possibly on NW and SE aspects.  These weak layers are now buried anywhere from 1.5' to 4' deep in the snowpack.  We have experienced a large avalanche cycle on these weak layers over the last 2 weeks.  Many of the suspect slopes have already avalanched, or the surface hoar has been compressed or collapsed and has started to gain strength.  With that said, observations are still finding these layers intact with reactive snowpack tests and we have had recent avalanches associated with these layers during our latest storm cycle.

The recent rain and heavy snow storms have just added additional weight and stress to these weak layers.  Large destructive avalanches, severe consequences, and remote triggering continue to remain possible today.    

recent observations

Observations from Andesite Peak (Donner Summit area) showed 6'' of heavy new storm snow in this area.  Sensitive wind slabs formed near and above treeline and intentionally human triggered avalanches were propagating wide distances.  These wind slabs were failing on a density change within the storm snow and were 8'' to 2' deep.  Buried surface hoar was found in this area intact and a small avalanche below treeline was thought to be caused by this weak layer.  Rain was observed up to 8000' in the early afternoon.

On Powderhouse Peak (Luther Pass areas) similar conditions existed.  Storm slabs and wind slabs were easily failing on the same storm density change.  Storm slabs in protected areas 6'' deep were reactive as well as wind slabs near ridges.  Snow levels hovered around 7700' in the morning and climbed higher into the afternoon.

Weather and CURRENT CONDITIONS
weather summary

High pressure will bring drier conditions to our area today and Thursday.  Slightly above average daytime temps expected for today with partly cloudy conditions.  Our next chance of a storm will be Friday and Saturday. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 19 to 22 deg. F.
Max. temperature in the last 24 hours: 32 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 35 to 40 mph
Maximum wind gust in the last 24 hours: 107 mph
New snowfall in the last 24 hours: 4 to 6 inches
Total snow depth: 60 to 68 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. Partly cloudy then becoming mostly cloudy. Mostly cloudy.
Temperatures: 36 to 42 deg. F. 22 to 28 deg. F. 37 to 43 deg. F.
Wind Direction: SW SW SW
Wind Speed: 15 to 30mph with gusts to 40mph decreasing to 10 to 20mph with gusts to 30mph in the afternoon. 10 to 20mph with gusts to 30mph in the evening then becoming light. Light winds becoming 15 to 20mph with gusts to 30mph in the afternoon.
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy then becoming partly cloudy. Partly cloudy then becoming mostly cloudy. Mostly cloudy.
Temperatures: 31 to 36 deg. F. 22 to 29 deg. F. 34 to 40 deg. F.
Wind Direction: W SW to SE SE to SW
Wind Speed: 35 to 40mph with gusts to 60mph decreasing to 25 to 30mph with gusts to 40mph in the afternoon. Southwest 20 to 25mph with gusts to 40mph then becoming southeast 10 to 15mph after midnight. Southeast 10 to 15mph increasing to southwest 35 to 40mph with gusts to 60mph in the afternoon.
Expected snowfall: 0 in. 0 in. 0 in.
Disclaimer

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