THIS AVALANCHE ADVISORY EXPIRED ON December 17, 2016 @ 6:56 am
Avalanche Advisory published on December 16, 2016 @ 6:56 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The Avalanche Hazard today is Considerable on upper elevation slopes.  The combination of over a foot of new, heavy snow falling on light density snow below and strong winds accompanying the storm Wednesday night have created a cohesive storm slab and a significant new load on leeward slopes. In addition, persistent weak layers are present in some of our sheltered, northerly terrain from early season storms.

How to read the advisory


  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Storm Slab
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The new snow interface will begin to strengthen over the next few days but the presence of a significant grauple layer in some areas will continue to be a problem as the overlying slab gains strength. This layer was widespread throughout the Tamarack Out of Bounds Terrain yesterday and found at the bottom of the new storm slab between 10 and 16 inches down in areas over 7000 feet.

Avalanche Problem 2: Wind Slab
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Northerly slopes have seen a fair amount of loading over the last week beginning with the light density snow at the beginning of the week and during the last storm.  Leeward slopes have significantly more snow than the surrounding aspects right now.  Some of these windloaded area are also harboring persistent weak layers that were formed from early season storms on sheltered/shaded terrain. 

recent observations

We toured north of Tamarack Resort yesterday and found a rapidly changing snowpack.  Dense, warm, wind impacted new snow left a slightly upside down snowpack that may provide some sporty crust skiing today.  We experienced a large collapse(whumpf) on a low angle slope near the starting zone of Wildwood Bowl.  We found snow depths ranging from 48-64 inches depending on the amount of wind loading and elevation in the upper portion of that area. Our test results showed a weak layer of newly deposited grauple near the beginning of the storm cycle. Compression Tests and Extended Column Test failed repeatedly on this layer which was about 15 inches down.  Hasty pits and mit pits showed the weak layer to be widespread. Our test scores showed a variety of low to moderate scores with clean, planar but resistant shears.  Near the ground we found rounding depth hoar that also failed in a deep tap test. The most notable observation is that right now we have a variable snowpack depending on location with different problems lingering from the October/November storms and newly deposited wind and storm instabilities.  The only way you are going to know what's happening where you are recreating is to dig in and find out. As we collect baseline info about the snowpack in a variety of areas, your observations are invaluable to painting the bigger West Central  snowpack picture.  You can submit observations through our site or by emailing us at forecast@payetteavalanche.org.

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weather

Expect to see snow showers tapering off today with an approaching Arctic air mass accompanied by increasing North winds expected to be in the 18-23 mph range by mid day.  The temperature will fall throughout the day bringing the coldest temperatures of the season thus far. Wind chills will be in the -8 to -18 range with an overnight low near -19 in the valleys.  Single digit highs with wind chills are going to make it feel even colder through the weekend.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: 40 percent chance of snow showers, temp falling throughout the day 20 percent chance of snow showers, COLD Partly sunny and cold
Temperatures: 23 and falling deg. F. -19 deg. F. 8 deg. F.
Wind direction: North NE NE
Wind speed: 7-11 6-9 6 becoming calm
Expected snowfall: less than 1/2 in. Trace in. 0 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: A 50 percent chance of snow showers. Cloudy, with a temperature falling to around 4 by 4pm. A 20 percent chance of snow showers before 11pm. Partly cloudy. Partly sunny and cold.
Temperatures: 19 falling to4 deg. F. -11 deg. F. -2 deg. F.
Wind direction: N N N then WNW
Wind speed: 10-15 increasing to 23 14-21 8-11
Expected snowfall: 1 in. 0 in. 0 in.
Disclaimer

This avalanche advisory is provided through a partnership between the Payette National Forest and the Payette Avalanche Center. This advisory covers the West Central Mountains between Hard Butte on the north and Council Mountain on the south. 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 at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.