THIS AVALANCHE ADVISORY EXPIRED ON January 7, 2017 @ 6:41 am
Avalanche Advisory published on January 6, 2017 @ 6:41 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The Avalanche Danger is Moderate on upper elevation slopes today. Variable winds through the week have created small wind slabs on wind exposed slopes over the last few days. Watch for wind sculpted/textured or pillowed areas and firmer pockets of older windslab near ridge tops and on wind exposed slopes.  Expect additional wind loading today and tonight as mostly South winds begin to increase accompanying the next storm system. 

 

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

This week, the upper elevations have been dominated by light to moderate Northerly winds which were able to move the 5 inches of light density snow around easily, these winds created soft new wind slabs on multiple aspects.  In addition, you can still find the affects of the wind from the weekend and the end of last week. Most of the wind slab problems are going to be found on the northerly aspects where new slabs have been formed on top of older windslabs. Watch for sculpted or stiff wind board on the windward aspects and rippled, chalky or hollow feeling/sounding pillows and drifts on steep leeward aspects. You should also be aware that some of the older wind slabs may be found well below the ridgelines on leeward terrain.  Practice safe travel protocols, and expose only one person at a time in wind loaded avalanche terrain. The best skiing and riding is still going to be found in more protected terrain that escaped the effects of the wind.

advisory discussion

Did you know: Only a small portion of our operating budget comes from the Forest Service.  We RELY on the the Friends of  the Payette Avalanche Center to help finance the forecasts that you use and the equipment we use to gather the information.  Our forecast sleds are overdue for replacement and we rely on these as important tools to provide reliable avalanche advisories to the public...don't let your local avalanche center end up with a pile of melted metal, plastic, and rubber on the side of the road!  If you want to see daily avalanche advisories continue, now is the time to support your FRIENDS, get involved and help the FRIENDS out, or make a tax deductible donation online.

recent observations

No new natural or human caused avalanches have been reported recently although the possibility of human caused avalanches in the upper elevation remains.  Weather models are showing quite a bit of disagreement about wind and snow totals as the next storm approaches. The models do agree that most of the moisture and energy from the storm will be well to the South of the West Central Mountains. We have been lucky so far with the way that our snowpack has formed but if we see significant snowfall through this storm cycle, the avalanche conditions will be changing significantly as well.  We have observed the formation of surface hoar, near surface faceting and wind slabs over the last few weeks, in addition we are still tracking the basal facets that are widespread throughout the advisory area.  While this layer of weak snow has shown much improvement over the last 2-3 weeks, we are still finding it in shallow, northerly terrain to be weak and causing somewhat concerning test results in some locations. Wednesday, George was able to trigger the entire slab near Twin Lakes with a moderate compression test score.  

 

weather

NWS SHORT TERM FX...Today through Saturday...Cold surface high will persist over the area through Saturday as upper flow shifts to the west and then southwest. Today is the coldest day with most sites staying well below 20 degrees for afternoon highs and wind chills near or below zero through the day. Expect the low stratus that has formed over southeast Oregon and lower Treasure Valley of southwest Idaho to erode this afternoon as dry air aloft works toward the surface. Warming aloft begins Friday night as flow shifts to the west. However the surface layer remains cold and with clear skies early in the night, temperatures will again drop quickly, going below zero for many sites. Combined with winds of 10 to 20 MPH in the Snake Plain (especially east of Boise) wind chill values will reach 10 to 25 degrees below zero in the coldest spots. Clouds increase toward Saturday morning as flow aloft transitions to the southwest. Southeast Oregon will see light snow develop early Saturday morning, shifting to southwest Idaho zones by afternoon. While the southwest flow will bring warmer temperatures aloft, this first round of precipitation will be all snow to the lowest valley floors.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: Patchy fog before 11am. Otherwise, mostly cloudy, then gradually becoming sunny and cold. Patchy fog. Otherwise, partly cloudy. A 40 percent chance of snow after 11am. Patchy fog before 11am. Otherwise, mostly cloudy.
Temperatures: 6 deg. F. -11 deg. F. 13 deg. F.
Wind direction: Variable E/NE Variable
Wind speed: Light Light Light
Expected snowfall: 0 in. 0 in. Less than 1/2 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: Partly sunny Partly cloudy A 40 percent chance of snow after 11am. Mostly cloudy.
Temperatures: 13 deg. F. 3 deg. F. 20 deg. F.
Wind direction: S S S
Wind speed: 7-10 9-13 13-17
Expected snowfall: 0 in. 0 in. Less than 1 inch 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.