THIS AVALANCHE ADVISORY EXPIRED ON December 21, 2015 @ 6:17 am
Avalanche Advisory published on December 20, 2015 @ 6:17 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The avalanche hazard is Considerable in upper elevation wind affected areas where you are likely to encounter wind slabs on multiple aspects. It is also likely that skiers or snowmobilers will trigger soft slab avalanches in the new snow layers on steep, wind protected lower elevation terrain. Careful snowpack evaluation, cautious routefinding, and conservative decision making will be essential while traveling in avalanche terrain, especially wind loaded aspects!

How to read the advisory


  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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It is still possible to trigger a shallow or deeper wind slab on multiple upper elevation aspects. Winds gusting into the 40+mph range hammered the upper elevations Friday and Friday night. Expect these slabs on East through W facing aspects in all open, exposed terrain. NE, N and NW will have the deepest deposition with more shallow crossloaded areas found on upper elevation East and West facing terrain features.

Avalanche Problem 2: Storm Slab
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Snow totals over the last 5 days have been impressive.  The PAC advisory area looks like it has a mid winter snowpack on the ground already this season. The storm slab that we are concerned about is mostly unconsolidated but continues to grow in depth.  Changes in temperatures over the last few days have left a series of subtle layers in the snowpack that will fail under the weight of a skier or snowmobiler on steep slopes. We have heard numerous reports of sleds in protected terrain triggering these layers in the  12-18 inch range which correlates exactly with what we have been finding in our snow pits. We have also seen quite a few naturals avalanches over the last few days in these layers on steep rollovers and other unsupported slopes. We are going to be adding another load of snow starting tomorrow which will only increase this problem.

Avalanche Problem 3: Loose Dry
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Loose dry avalanches or sluffs are becoming more of a problem. We have a lot of unconsolidated snow on the ground, if you are in steep or confined terrain these small slides can push you off course and into or over obstacles you would rather avoid. Be aware of where your partners are and don't push a sluff down on to them. As the snow gets deeper this problem will continue to be a problem.

advisory discussion

During the week last week, PAC forecasters encountered layers of buried surface hoar in both the Northern and Southern ends of our advisory area.  These layers were not widespread or well formed and were created during very brief periods of clearing and cooling between storms.  These layers should continue to degrade with the weight of the new snow smashing them down. Keep in mind that you may still encounter these in isolated, wind protected areas.  If you are digging around and find these layers, please shoot us an email or enter an observation to let us know where you found them.

recent observations

We saw and  had reports of soft slabs breaking loose in steeper terrain yesterday.  These slabs are releasing between 12 and 18 inches down in the new snow layers that have accumulated over the last 4-5 days. Wind loaded areas continue to be our primary concern.  

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
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weather

Look for partial clearing this morning and cooler temperatures today with light accumulations possible in the mountains.  Another strong winter storm will enter our area tomorrow with pre-frontal winds gusting into the high twenties and mid thirties.  A strong NW zonal flow will provide nearly continuous precipitation through Thursday night with a strong cold front entering the area toward the end of the week and keeping temperatures below normal.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Sunday Sunday Night Monday
Weather: Snow showers after 11am. Steady temperature around 17. Wind chill values between -3 and 5. Breezy, with a south southwest wind 11 to 16 mph increasing to 19 to 24 mph in the afternoon. Chance of precipitation is 80%. Total daytime snow accumulation of 1 to 2 inches possible. Snow showers, mainly before 11pm. Low around 16. Breezy, with a west southwest wind 20 to 25 mph decreasing to 14 to 19 mph in the evening. Winds could gust as high as 34 mph. Chance of precipitation is 80%. New snow accumulation of 2 to 4 inches possible. Snow. High near 25. Breezy, with a southwest wind 15 to 20 mph increasing to 23 to 28 mph in the afternoon. Chance of precipitation is 100%. New snow accumulation of 4 to 8 inches possible
Temperatures: 17 deg. F. 16 deg. F. 25 deg. F.
Wind direction: S/SW W/SW SW 15-20
Wind speed: 11-16 increasing in the afternoon. 20-25 gusting to 34 increasing in the afternoon.
Expected snowfall: 1-2 in. 2-4 in. 4-8 in.
Granite Mountain at 7700 feet.
  Sunday Sunday Night Monday
Weather: Snow showers after 11am. Areas of dense fog before 11am. High near 26. Calm wind becoming south southeast 5 to 9 mph in the afternoon. Chance of precipitation is 80%. Total daytime snow accumulation of around an inch possible. Snow showers, mainly before 11pm. Low around 20. South southeast wind 6 to 13 mph. Chance of precipitation is 90%. New snow accumulation of 1 to 2 inches possible. Snow, mainly after 11am. High near 28. Light south wind becoming south southeast 6 to 11 mph in the morning. Chance of precipitation is 100%. New snow accumulation of 2 to 4 inches possible.
Temperatures: 26 deg. F. 20 deg. F. 28 deg. F.
Wind direction: S/SE S/SE S becoming S/SE
Wind speed: 5-9 6-13 14-16
Expected snowfall: 1 in. 1-2 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.