THIS AVALANCHE ADVISORY EXPIRED ON December 19, 2016 @ 6:07 am
Avalanche Advisory published on December 18, 2016 @ 6:07 am
Issued by -
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The avalanche danger today is MODERATE on all upper and mid elevation slopes. Wind slabs can be found near ridges and mid slope on upper elevation, wind affected terrain.  Additionally, it may be possible to trigger avalanches up to 1.5 feet deep on steep, wind protected slopes at the interface between the old snow and the newer snow from our last storm event.

How to read the advisory


  • 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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Wind slabs deposited during the storm are probably mostly eroded out now with a dense sastrugi wind board replacing them on all upper elevation wind affected terrain. Be weary of any slopes or terrain features that are on leeward aspects of obvious wind eroded slopes.

Winds were light yesterday out of the north and northwest, nevertheless, most snow that was available for transport got blown by Fridays northerly winds. Even though many aspects have been eroded by recent winds, due keep a look out for smooth and rounded (often describe as lens shaped), hollow sounding slopes. If you see shallow cracks coming off your skis today you are probably on or approaching a wind slab.

Avalanche Problem 2: Storm Slab
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The interface between this week's new snow and the older snow below will likely continue to be our layer of concern until we have another significant storm. In the northern portion of the advisory area we were unable to find the thick grauple layer that we found on West Mountain earlier this week. The density change is enough to create the hazard of storm slabs up to 1.5 feet thick in some areas.  Where the grauple layer is present it is more likely to propagate making it easier to trigger the storm slab above.  

advisory discussion

A YUUUUGGE thank you to all that came out to the Backcountry Film Festival last night! It was a very cold night outside, but near 200 people braved the elements to help raise money for McCall Winter Sports Club and the Payette Avalanche Center! 

recent observations

No new natural or human triggered avalanches have been reported since our last onslaught of snow on Thursday. Snowmobiling and touring conditions have been COLD. 

Worth noting is the widespread presence of a layer cake of rounding but faceted snow resting above and below an ice crust near the bottom of the snowpack in many areas where the October snow was preserved. This is likely the layer that has been producing the random collapsing or whumphing of the snowpack in some areas. This layer has been producing sudden planar shears when loaded in deep tests but is likely below the stress bubble of a skier or snowmobile in all but very shallow areas.

From a recreational standpoint the skiing was better than expected, travel was easy with about 30 cm ski penetration on protected slopes. Sleds are still digging through the snowpack to the ground in many places.  We could not believe what we saw that had been "uncovered" by sleds off trail yesterday. Coverage is still thin with just enough new snow to camouflage many of the buried obstacles.  Lower elevation slopes are a mine field of stumps and downed trees. Be careful out there!

weather

Another cold morning is upon us with temperatures around the advisory area hovering around -10 degrees Fahrenheit at 5am, but a change is not far off. Today expect clear and sunny skies with a max of around 10 degrees. Frigid temperatures will begin to moderate tonight and into tomorrow ahead of an approaching trough of moisture from the Gulf of Alaska. Models are currently showing near 1 inch of water, equating to about 10 to 15 inches of snow by Wednesday morning in the upper elevations of the PAC advisory area.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Sunday Sunday Night Monday
Weather: Mostly sunny and cold, with a high near 8. Wind chill values between -10 and -20. Light and variable wind. Mostly cloudy, with a low around 1. Calm wind. Snow showers likely, mainly after 11am. Cloudy, with a high near 20. Wind chill values between -4 and 6. South southeast wind 5 to 8 mph. Chance of precipitation is 60%. New snow accumulation of 1 to 2 inches possible.
Temperatures: High 8 deg. F. Low 1 deg. F. High 20 deg. F.
Wind direction: Variable Calm S/SE
Wind speed: Light 5 to 8
Expected snowfall: 0 in. 0 in. 1 to 2 in.
Granite Mountain at 7700 feet.
  Sunday Sunday Night Monday
Weather: Mostly sunny and cold, with a high near 10. Wind chill values between -20 and -30. West wind 11 to 18 mph. Mostly cloudy, with a low around 5. Wind chill values between -8 and -18. Breezy, with a west southwest wind 14 to 19 mph increasing to 23 to 28 mph after midnight. Snow showers likely, mainly after 11am. Cloudy, with a high near 22. Wind chill values between -4 and -14. Windy, with a west southwest wind 24 to 31 mph, with gusts as high as 40 mph. Chance of precipitation is 70%. New snow accumulation of 1 to 3 inches possible.
Temperatures: High 10 deg. F. Low 5 deg. F. High 22 deg. F.
Wind direction: West W/SW W/SW
Wind speed: 11 to 18 14 to 19 24 to 31 gusting 40
Expected snowfall: 0 in. 0 in. 1 to 3 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.