THIS AVALANCHE ADVISORY EXPIRED ON December 25, 2016 @ 7:15 am
Avalanche Advisory published on December 24, 2016 @ 7:15 am
Issued by Dave Bingaman - Payette Avalanche Center
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The avalanche danger is Considerable above 7000 feet today. Gusting and variable winds have created sensitive wind slabs near ridgetops and on the leeward side of smaller terrain features. 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. The potential for new storm slabs up 10 inches thick exists in steep upper elevation terrain.

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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We have been finding small wind slabs and large wind drifts near the ridgetops on multiple aspects over the last week.  Winds have swirled around the compass from  S/SW  to N/NW  and have been sculpting and transporting the light density snow that has accompanied the last 2 storms. Yesterday we observed active loading on the backcountry terrain north of Tamarack Resort. Over the next 12-24 hours we will see winds continuing to gust in the upper elevations into the mid 20 mph range creating another round of wind slabs at or near the ridgelines.  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 24 hours. Expect to see 10 plus in the upper elevations, with over a foot by Christmas afternoon.  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 10 inches 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 in multiple location 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.  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

There are a number of great beginner avalanche classes coming up for both skiers and snowmobilers. 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

We toured out of bounds at Tamarack Resort yesterday and found moguls on a lot of steep north facing terrain...the same terrain that is harboring the weakest spots in the snowpack.  We found a strengthening slab overlying the facets near the ground on multiple aspects as well as some upper snowpack instabilities including the grauple layer from the warm storm 2 weeks ago. Overall strength was improving but there still exists a possibility of triggering a potentially fatal slide on shallow or rocky terrain. Our pit tests showed failures that were hard to initiate but provided very quick and clean shears in the faceted snow near the ground. Moderate verging on strong winds were easily moving the 2-3 inches of new snow and loading Northerly aspects throughout the day.

weather

Most of our local Snotel sites and the ski areas are reporting 5-7 inches of new snow overnight at the 6500 ft level.  Winds were easily moving snow yesterday and will be gusting into the mid 20's today.  Snow will continue through the day today and then taper off tonight with cloudy skies and a chance of snow before noon on Christmas Day.  The upper elevations could pick up an additional 3-6 inches before that happens.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: Snow Cloudy-50% chance of precipitation Cloudy-30% chance of precipitation
Temperatures: 26 deg. F. 16 deg. F. 22 deg. F.
Wind direction: N/NW N/NW NW
Wind speed: 3-8 5-8 5
Expected snowfall: 1-2 in. Trace in. Trace in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: Snow Snow Snow
Temperatures: 24 deg. F. 12 deg. F. 18 deg. F.
Wind direction: N N N
Wind speed: 7-16 Around 17 9-16
Expected snowfall: 1-3 in. 1-2 in. <1 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.