THIS AVALANCHE ADVISORY EXPIRED ON December 27, 2016 @ 6:10 am
Avalanche Advisory published on December 26, 2016 @ 6:10 am
Issued by -
bottom line

The avalanche danger is MODERATE today in the upper and mid elevations due to human triggered avalanches being possible. Below 6,000 feet the danger is LOW.  Wind slabs near ridge tops will be the main concern today, but there is also a low probability/high consequence of triggering a persistent slab 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 over the last few days and have been sculpting and transporting the 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 out of the south southwest. 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: 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 slab if it fails. 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.  If you are ready to take the next step after KBYG, PAC still has room for both skiers and snowmobilers in our upcoming Intro to Avalanches class on Jan 6 and 7, registration by email is required.

recent observations

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

The snow that we received Friday and Saturday 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 ridge tops, on exposed upper elevation slopes, and on smaller terrain features such as gullies and sub ridges will be your main concern today.

weather

The mountains of the PAC advisory area picked up no new snow overnight and winds were light out of the south southwest. Today expect to have partly sunny skies with winds out of the south southwest blowing 9 to 16 mph and gusts will be in the 20's. An approaching storm front will cause an increase in clouds this afternoon, and snowfall will begin tonight around midnight. By morning 1 to 4 inches should blanket the upper elevations of the advisory area, and another 4 to 10 inches are possible during the day tomorrow.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Monday Monday Night Tuesday
Weather: Patchy fog before 11am. Otherwise, mostly cloudy, with a high near 15. South wind around 5 mph. Snow likely after 11pm. Cloudy, with a temperature rising to around 18 by 5am. South southeast wind around 6 mph. Chance of precipitation is 70%. New snow accumulation of less than one inch possible. Snow. High near 23. South wind around 7 mph. Chance of precipitation is 90%. New snow accumulation of 2 to 4 inches possible.
Temperatures: High 15 deg. F. Rising to 18 deg. F. High 23 deg. F.
Wind direction: South South southeast South
Wind speed: 5 6 7
Expected snowfall: 0 in. less than 1 in. 2 to 4 in.
Granite Mountain at 7700 feet.
  Monday Monday Night Tuesday
Weather: Mostly cloudy, with a high near 16. Wind chill values between zero and 5. South southwest wind 8 to 14 mph. Snow after midnight. Low around 12. Wind chill values between -4 and 2. Breezy, with a south southwest wind 15 to 23 mph, with gusts as high as 32 mph. Chance of precipitation is 90%. New snow accumulation of 1 to 2 inches possible. Snow. High near 22. Breezy, with a southwest wind 21 to 23 mph. Chance of precipitation is 100%. New snow accumulation of 4 to 8 inches possible.
Temperatures: High 16 deg. F. Low 12 deg. F. High 22 deg. F.
Wind direction: South southwest South southwest Southwest
Wind speed: 8 to 14 15 to 23 21 to 23
Expected snowfall: 0 in. 1 to 2 in. 4 to 8 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.