THIS AVALANCHE ADVISORY EXPIRED ON December 21, 2016 @ 6:36 am
Avalanche Advisory published on December 20, 2016 @ 6:36 am
Issued by -
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The avalanche danger will start out MODERATE this morning in all avalanche terrain over 6,000 feet, but will quickly jump to CONSIDERABLE above 7,000 feet due to the incoming snow and strong winds. Once the snow starts to accumulate human avalanches will be likely in wind loaded terrain above 7,000 feet.

Below 6,000 feet the avalanche danger will be LOW.

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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Today we will see a new batch of wind slabs form on northwest, north, northeast, and east terrain, and wind slabs will be 1 to 2 feet deep.

The wind slabs we have been talking about the last few days have slowly stiffened and become harder to trigger. Whereas today, the new wind slabs will be much more sensitive and easy to trigger. On the northwest, north, northeast aspects these new slabs will be forming on a mostly wind scoured surface from our north winds over the weekend, making for a very poor bond between the new and old snow.  On the south half of the compass if you do find any wind loading in isolated areas, of the upper elevations, they will have formed on old stiff wind slabs that could avalanche with the new snow. 

To travel safely today, it is going to be important to keep your eyes out for obvious signs of wind loading. Be on the lookout for 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.

Avalanche Problem 2: Storm Slab
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If forecasted snowfalls materialize, storm slabs will be possible. A storm slab is a soft cohesive layer or slab of new snow which breaks on the old snow surface. This problem will be especially evident in areas that have not been affected by today's winds, but the new snow is/has fallen on a previously wind scoured surface. While traveling in avalanche terrain today it will be essential to do lots of quick hand pits to assess how the new snow is bonding with the old snow surface. Is it easy to pull new snow off in a soft and cohesive slab? Does that new soft slab shear easily from the old snow surface? 

advisory discussion

We have a number of great beginner avalanche classes coming up. Be sure to check out 'local classes' under the Education tab at the top of the forecast page. If already have the basics down and are ready to take your Level One, do it. Make staying safe while playing in avalanche terrain a New Year's Resolution!

recent observations

No new natural or human caused avalanches have been seen or reported.

Yesterday we toured from Lick Creek Summit during the arrival of our current storm. Conditions were windy, and lots of signs of obvious wind scouring and wind loading. We dug a pit on a north-northwest aspect that had not been affected by the winds. We did not find the groupel layer that we found on West Mountain, and unlike many other zones around the advisory area the snowpack in this particular spot was 'right side up'. We did have a failure during our compression test. It was a CT-25 (5th blow using the whole arm from the shoulder) at 25 cms from the ground (in a 145 cm snowpack) at the hardness change between rounding basal facets and melt freeze grains, and the fracture character was resistant planar. 

weather

A WINTER STORM WARNING is in effect until 5 pm today.

As of 5 am it is a balmy 18 degrees at the summit of Brundage this morning, and 21 in McCall. Currently between 1 and 3 inches of new snow has fallen in the mountains with winds out of the south-southwest blowing in the 20's and gusting into the 30's. Today expect to see more snow and wind with 7 to 10 inches of additional snow and moderate to strong winds. 

Wednesday will be clear and calm, and our next significant weather system will impact the PAC advisory area Friday night into Saturday.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Tuesday Tuesday Night Wednesday
Weather: Snow. High near 27. South wind around 9 mph. Chance of precipitation is 90%. Total daytime snow accumulation of 3 to 5 inches possible. A 30 percent chance of snow before 11pm. Mostly cloudy, then gradually becoming mostly clear, with a low around 7. West southwest wind 5 to 7 mph becoming calm in the evening. New snow accumulation of less than a half inch possible. Mostly sunny, with a high near 22. Wind chill values between -2 and 8. East northeast wind around 5 mph becoming light and variable.
Temperatures: High 27 deg. F. Low 7 deg. F. High 22 deg. F.
Wind direction: South West-southwest East-northeast
Wind speed: 9 5 to 7 5
Expected snowfall: 3 to 5 in. less than 0.5 in. 0 in.
Granite Mountain at 7700 feet.
  Tuesday Tuesday Night Wednesday
Weather: Snow. High near 28. Windy, with a west wind 26 to 34 mph, with gusts as high as 46 mph. Chance of precipitation is 100%. Total daytime snow accumulation of 3 to 7 inches possible. A 30 percent chance of snow, mainly before 11pm. Mostly cloudy, then gradually becoming mostly clear, with a low around 8. Northwest wind 8 to 18 mph. New snow accumulation of less than a half inch possible. Mostly sunny, with a high near 20. Wind chill values between -2 and 8. Northwest wind 6 to 9 mph becoming southwest in the afternoon.
Temperatures: High 28 deg. F. Low 8 deg. F. High 20 deg. F.
Wind direction: West Northwest Northwest
Wind speed: 26 to 34 gusting 46 8 to 18 6 to 9
Expected snowfall: 3 to 7 in. Less than 0.5 in. 0 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.