THIS AVALANCHE ADVISORY EXPIRED ON December 20, 2016 @ 5:25 am
Avalanche Advisory published on December 19, 2016 @ 5:25 am
Issued by -
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The avalanche danger today is MODERATE on all avalanche terrain above 6,000 feet, human triggered avalanches are possible. 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.

Below 6,000 generally safe avalanche conditions exist.

How to read the advisory


  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Persistent Slab
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While by definition, graupel is not a persistent grain, it is making for a persistent slab problem. Graupel tends to become faceted easily when subjected to a strong temperature gradient, in which case, graupel produces avalanches much more persistently. We have mostly found graupel in the snowpack in the southern portions of our advisory area (West Mountain), and we were unable to find graupel in the northern portion. However, that does not mean it's not there. It is because of this, that when I go out today, I will be on the look out for this layer. Where the grauple layer is present it is more likely to propagate, making it easier to trigger the slab above.  

Secondly, where the graupel does not exist, the change in hardness between last Thursday's new snow and the older snow below continues to be of concern. The hardness change is enough to create the danger of a slab up to 1.5 feet thick in some areas.  

Avalanche Problem 2: Wind Slab
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We have had a mix bag of winds in the upper elevations over the last four days. Because of this it is going to be important to keep your eyes out for obvious signs of windloading. While these windslabs may not be big, they could easily take you and your sled somewhere you don't want to be. As you are traveling today, make note of wind scouring and loading (lens shaped slabs), keep an eye out for cracking of surface snow, and make terrain decisions that (in a worst case scenario) would not cause you to be taken over cliffs or into a terrain trap.

advisory discussion

Now is a good time to get a base line of the snowpack in your favorite skiing and riding areas. This is due to the fact, that as we see this next significat storm start to pile up in the  mountains around us it will be good to know what is under our skis and sleds so we can make safe decisions.

recent observations

No new natural or human avlanches have been seen or reported within the PAC advisory area. We continue to see obvious signs of wind scouring on windward aspecst, and windloading on the leeward aspects. The interface between old snow and last Thursday's storm snow continues to be the layer that most easily fails during our snowpack assesments. This failure is due to a hardness change in the pack, and in some areas a graupel layer. The only way to know if this graupel layer exists where you are skiing or riding today is to dig into the snow 1 to 2 feet and see. 

weather

Yet another cold morning is upon us, but a change is a coming. Today we will see the arrival of warm and wet front that will cause for heavy snowfall around the PAC advisory area. A winter storm warning has been issued starting Monday night through Tuesday afternoon due to upwards of 1 inch of snow water equivalent (SWE) and strong winds. With the temperatures that are forecasted, by Wednesday morning we should see 10 to 15 inches of new snow in the mountain of the PAC advisory area.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Monday Monday Night Tuesday
Weather: Snow likely, mainly after 11am. Cloudy, with a high near 19. Wind chill values between -7 and -17. South wind 9 to 14 mph. Chance of precipitation is 70%. New snow accumulation of 1 to 3 inches possible. Snow. Temperature rising to around 28 by 4am. South wind 8 to 11 mph. Chance of precipitation is 90%. New snow accumulation of 3 to 5 inches possible. Snow. High near 31. Southwest wind 11 to 13 mph. Chance of precipitation is 100%. New snow accumulation of 3 to 5 inches possible.
Temperatures: High 19 deg. F. Rising to 28 deg. F. High 31 deg. F.
Wind direction: South South Southwest
Wind speed: 9 to 14 8 to 11 11 to 13
Expected snowfall: 1 to 3 in. 3 to 5 in. 3 to 5 in.
Granite Mountain at 7700 feet.
  Monday Monday Night Tuesday
Weather: Snow likely, mainly after 11am. Cloudy, with a high near 19. Wind chill values between -4 and -14. Breezy, with a west wind 21 to 26 mph. Chance of precipitation is 70%. New snow accumulation of 1 to 3 inches possible. Snow. Temperature rising to around 25 by 4am. Windy, with a west southwest wind 11 to 16 mph increasing to 25 to 30 mph after midnight. Winds could gust as high as 39 mph. Chance of precipitation is 100%. New snow accumulation of 3 to 7 inches possible. Snow. High near 27. Breezy, with a west wind 24 to 29 mph, with gusts as high as 38 mph. Chance of precipitation is 100%. New snow accumulation of 5 to 9 inches possible.
Temperatures: High 19 deg. F. Rising to 25 deg. F. High 27 deg. F.
Wind direction: West W/SW West
Wind speed: 21 to 26 11 to 16 gusting to 39 24 to 29 gusting to 38
Expected snowfall: 1 to 3 in. 3 to 7 in. 5 to 9 in.
Disclaimer

This avalanche advisory is provided through a partnership between the Payette National Forest and the Friends of 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.