THIS AVALANCHE ADVISORY EXPIRED ON March 27, 2016 @ 6:56 am
Avalanche Advisory published on March 26, 2016 @ 6:56 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The Avalanche Danger is Moderate on upper elevation windloaded or crossloaded slopes.  Human triggered wind slabs are likely however in steep, northerly and east facing terrain where new wind slabs formed Thursday and Friday. Expect to find new wind slabs that will be reactive to the weight of a skier or snowmobile ranging in depth from a few inches to a foot or more.  Slopes that were protected from the winds will have better stability and Low danger. 

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
    Large
    Small

Wind slabs continue to be our biggest concern today.  We observed widespread wind transport of the new snow on Friday as winds ramped up in the afternoon and swirled from the SW to the W through the day.  Expect to find new and sensitive windslabs on upper elevation, SE, E, NE, N and NW slopes today. Given the velocity of the winds and the light snow that was available for transport, you can expect to find wind deposited  and crossloaded snow much further below the ridges than we have seen over the last few days of relatively light winds.  Expect to see pillows, spindrift cones and other tell tale signs of wind blown snow below steep or rocky headwalls and lower down in northerly terrain than normal.

By Friday afternoon, we were able to ski cut the freshly formed slabs on steep leeward terrain to a depth of about 6 inches. Some of these slabs formed not only on the unconsolidated snow in the northern aspects but also on a variety of other snow surfaces including crusts and grauple deposits.  Some of these layers will increase the speed of and the ability of the overlying wind slab to propagate. Take the time to check out the upper 2-3 feet of the snowpack before you commit to any steep terrain.

Skiers in Lick Creek also reported a small skier triggered wind slab Friday afternoon on a NE slope and widespread wind slab formation that got deeper as they went up in elevation. 

You can expect to find shallow and deeper(possibly close to 2 feet?) wind slabs throughout the northern aspects with crossloaded areas on small ridges and gullies or other depressions.  Look for tell tale visual clues and don't ignore cracking or hollow feeling snow beneath your skis or sled today.

Note the visual clues on the snow surface and the growing wind slab on the right edge of the photo.

 

advisory discussion

This week marks the end of the regular PAC advisory season. We will be doing periodic and weekend updates as conditions change.  There is still plenty of winter left in the mountains, but the PAC budget melted out a little early this year. We want to extend a BIG thank you to the Friends of the Payette Avalanche Center Board of Directors for their financial support as well as to all of our volunteer travel companions that join us in ALL kinds of weather and conditions.

Pay attention to rapidly changing spring conditions while you are out in the mountains and if you see or trigger avalanche activity, please take the time to get in touch with us. Remember your information can save lives. If you see anything we should know about, let us know by clicking the OBSERVATION tab at the top of the page. Or by calling/emailing directly 208-634-0419 or forecast@payetteavalanche.org.  If you are getting out and enjoying any spring skiing/riding we would like to know, any information is good information!  

recent observations

Friday we toured around on the West edge of Squaw Point and found good skiing in protected terrain, moderate to strong winds , huge wind drifts and tree wells as well as rapidly forming wind slabs.  The winds also did a great job of crossloading sub ridges and gullies on the W, NW terrain we were skiing, quickly forming shallow and reactive wind slabs.

Everywhere we looked we were amazed at the size and amount of cornices overhanging ridges and bowls, and even mid elevation sub-ridges and smaller terrain features. It has truly been a windy winter. Pay attention to these beasts when it warms up again as they begin to fail. The upper 18 inches of the snowpack above last weekend's melt freeze crust looked very good and has begun to consolidate from the crust up providing pretty good stability in the new snow we got this week. Below the crust there are still some weak layers preserved that may linger through the end of the season. These deeper layers will likely continue to be hard to trigger until we see another major warm up.

Photos are: the amount of snow drifted over our sleds in the 4 hours that we were away from them and a W/NW ridgeline with a 20 +foot cornice at 7500 feet and the effects of the wind where you can see some ripples and drifts forming across the small slope.

      

weather

Expect sunny skies today with the possibility of a few high clouds later in the day, upper elevation highs will be in the mid 30's.  Light S/SW winds and a low tonight around 24. A cold front will move into the area early Sunday bringing a dusting of new snow to the valley floor in McCall and 2-4 inches to the mountains.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: Sunny, with a high near 40. Calm wind becoming south around 6 mph in the afternoon. Partly cloudy, with a low around 26. South wind around 5 mph becoming calm in the evening. Snow showers likely, mainly after noon. Mostly cloudy, with a high near 37. Light and variable wind becoming south southwest around 6 mph in the morning. Chance of precipitation is 70%. New snow accumulation of less than one inch possible.
Temperatures: 40 deg. F. 26 deg. F. 37 deg. F.
Wind direction: Calm becoming S S S/SW
Wind speed: 6 26 6
Expected snowfall: 0 in. 0 in. 1 in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: Sunny, with a high near 35. Light and variable wind becoming south southwest 5 to 10 mph in the afternoon Partly cloudy, with a low around 24. South wind 7 to 9 mph. Snow showers. High near 34. South southwest wind 10 to 15 mph. Chance of precipitation is 80%. New snow accumulation of 2 to 4 inches possible.
Temperatures: 35 deg. F. 24 deg. F. 34 deg. F.
Wind direction: Light and variable becoming S/SW S S/SW
Wind speed: 5-10 7-9 10-15
Expected snowfall: 0 in. 0 in. 2-4 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.