THIS AVALANCHE ADVISORY EXPIRED ON December 26, 2016 @ 6:51 am
Avalanche Advisory published on December 25, 2016 @ 6:51 am
Issued by Dave Bingaman - Payette Avalanche Center
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Merry Christmas! The avalanche hazard is Moderate today in the upper and mid elevations and low below 6000 feet.  Wind slabs near ridgetops will be the main concern today. The potential for storm slabs up to 12 inches thick exists in steep. upper elevation terrain. There is also a low probability/high consequence possibility of triggering a large avalanche in shallow/rocky areas where a layer of faceted snow at the ground has 3 to 5 feet of snow resting above it.

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
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We have been finding small wind slabs and large wind drifts near the ridgetops on multiple aspects over the last week. In some areas, these slabs are resting on a slick wind crust. Winds have swirled around the compass from over the last few days and have been sculpting and transporting the light density snow that has accompanied the last 2 storms.  Over the next 12-24 hours we will see winds continuing to gust in the upper elevations into the mid 20 mph range and then switching to the South before calming. Be aware of crossloaded areas on smaller terrain features and watch out for obvious clues like cracking or hollow sounding/feeling snow under your skis or track.

Avalanche Problem 2: Storm Slab
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Most of our mid elevation reporting sites picked up 5-7 inches of new snow in the last 48 hours bringing snow totals for the week up to just about 12 inches. Be cautious of the interface between the older, firm snow which was downright slick on some wind scoured upper elevation slopes, and the new snow above. On wind protected slopes the new snow may be resting on a newly formed layer of Surface Hoar which is a very weak layer.  Anticipate soft storm slabs of up to 12 inches thick on terrain steep enough to slide today.

Avalanche Problem 3: Persistent Slab
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We have found a weak layer near the ground throughout the advisory area over the last two weeks that is made up of weak faceted snow or a combination of facets and old crusts left over from our early season snowpack.  The weak layer of facets is fairly widespread and well developed in the upper elevations especially on the shadier aspects where early snowfall accumulated. Shallow rocky areas are also harboring this layer on other aspects.  George described this problem earlier this week as a low probability/ high consequence avalanche problem...meaning you are not very likely to trigger a slide this deep but the consequences if you did would be bad.  The 3-5 foot overlying slab is gaining strength which is good but is also turning into more of a hard, consolidated meat grinder if it fails. The mostly slow and incremental loading of new snow on this layer has not come close to overloading the strength of the slab above it yet but with additional snow last night and today and the addition of wind loaded snow in the Northerly terrain, now is a good time to play it safe on steep shady slopes or slopes with thinner/rocky areas where you are more likely to trigger the weak layer.  

This kind of problem is both difficult to trigger and more difficult to predict.  Slopes with tracks on them are not a good indicator of stability as the trigger points are likely to be isolated to thin or weak spots that are hard to find or easy to miss.  Remember that a lack of red flags or signs of instabilities is not a good indicator for a deep or persistent slab problem.  Don't let the lack of evidence lull you into more consequential terrain or sloppy group management.  Use good travel techniques(one at a time) and watch your partners if you are riding or sliding in this type of terrain.

 

 

 

advisory discussion

Don't forget about our Know Before You Go class coming up this Tuesday evening at the McCall Ranger District office. KBYG is a great first step or a quick review if you are planning on heading into the backcountry and want to stay safe.  Also, PAC  and the Friends still have room for both skiers and snowmobilers in our upcoming Intro to Avalanches class on Jan 6 and 7, registration by email is required.

There are a number of great beginner avalanche classes coming up for both skiers and snowmobilers throughout the area. Be sure to check out 'local classes'  or upcoming events under the Education tab at the top of the forecast page. If you already have the basics down and are ready to take your Level One, skiers and snowmobilers can find classes this winter around the state, don't make excuses, just do it!  Make staying safe while playing in avalanche terrain a New Year's Resolution!

recent observations

Winds were mostly light yesterday with some gusts reaching into the 20's and 30's yesterday afternoon and overnight.  The snow that we received came in with slightly warmer temperatures but did little to form a cohesive slab.  The formation of isolated wind slabs on multiple aspects near the ridgetops, on exposed upper elevation slopes and on smaller terrain features such as gullies and sub ridges will be your main concern today.

Santa was observed making his way through the pow yesterday at local resorts.  No observations were made or reported from the local snowmobile lots...

                                                          

weather

Expect scattered snow flurries throughout the day today with clearing and cold temps for Monday.  Another significant storm will enter the area on Monday night and produce significant snow throughout the West Central by mid-week.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Sunday Sunday Night Monday
Weather: 20% Chance of snow, cloudy Patchy fog Patchy fog
Temperatures: 21 deg. F. 0 deg. F. 14 deg. F.
Wind direction: NW NNW S
Wind speed: Around 5 Around 5 Around 5
Expected snowfall: Trace in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Sunday Sunday Night Monday
Weather: Cloudy, 30 % chance of snow before 11am Mostly cloudy Partly Sunny
Temperatures: 17 deg. F. 4 deg. F. 16 deg. F.
Wind direction: N N becoming S S
Wind speed: 9-15 5-8 8-14
Expected snowfall: < 1/2 in. 0 in. 0 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.