Avalanche Advisory published on January 4, 2019 @ 7:02 am
Issued by Dave Bingaman - Payette Avalanche Center
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Moderate Avalanche hazard exists throughout the West Central Mountains.  Wind Slabs are the primary concern and exist in exposed, upper elevation terrain.  These slabs have potential to "step down" into weak layers deeper in the snowpack.  Avalanches are also possible in wind protected areas where buried weak layers exist within the snow pack.  Your safest option is to avoid steep terrain, especially areas where the snow pack is still thin enough to trigger the sugary, faceted layer near the ground.

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
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

Winds over the last week have created wind slabs on a variety of upper elevation slopes.  Monday we recorded large plumes of snow on most of the peaks and exposed terrain near Lick Creek Summit including one substantial natural avalanche that had released during the wind event.  Wind slabs are easy to see and will show up as drifts, pillows or textured snow where the wind has been working.  The wind slabs that we have seen this week run the spectrum from soft to very firm.  Some can produce cracking near the surface, others will allow you to easily travel on top of them.  The broken record message regarding these wind slabs is that one they can take you for a ride or cause significant hazard by themselves but the big concern is that if triggered, they may have the ability to "step down" into the buried weak layers below creating a much larger and dangerous avalanche scenario.  The potential for a human triggered avalanche in these deep layers is declining with time but the potential for a smaller avalanche triggering a larger one is something that has kept wary backcountry travelers out of steep wind affected terrain so far this winter.

Avalanche Problem 2: Persistent Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

Our snowpack continues to show us reasons not to venture into steep, consequential terrain right now.  Despite the fact that we have not seen any new avalanches in 2 buried weak layers in the last 3 weeks, we still have a VERY unusual snowpack for the West Central Mountains.  The cold temperatures that we have seen so far have allowed these layers to remain a concern, especially in areas where the snowpack is still thin enough for a sledder or skier to affect them.

 Cautious travel is advised, the weak layers that continue to get deeper in our snowpack are refusing to go away quickly this year.  While the upper snowpack continues to gain strength and depth, the weakest layer of Basal Facets(near the ground) continues to show the ability to both initiate and propagate avalanches that would run to the ground.  A weak layer in the middle of the snowpack continues to produce failures in our pit tests too.  This is a layer of Surface Hoar and Near Surface Facets that are getting stronger in most cases but remain well preserved in others.  Here is a video of a Propagation Saw Test that we did Wednesday to test this layer, it showed ample ability to propagate if initiated.   A series of storms combined with a warming trend early next week and the potential for moderate  snow accumulations may be just the ticket to trigger another round of natural avalanches in these layers or give us a chance for them to start to heal.

North East aspect 7600 ft pit showing buried weak layers and wind affect on surface

South West Aspect 7250 ft showing a fairly well consolidated upper pack on a weak layer near the ground

advisory discussion

Due to the partial government shutdown, avalanche forecasting will be limited.  We expect to forecast 3 times a week until the shutdown has ended.

Join FPAC and PAC forecasters for a benefit and social at Broken Horn Brewing on January 10 at 6PM.  $1 of every pint sold goes to the FPAC.

Your observations are very helpful to the PAC staff and help create a better picture of the complex terrain in our advisory area.  You can click on the add observations linkand add as little or as much detail as you have.  It is easy to navigate and will also upload pictures easily.  Please contribute to your local forecast by sharing what you see or experience even if it is just good snow. or a trip report.

recent observations

Good skiing and riding can be found on almost all aspects right now.  South facing slopes have received just enough solar gain this week to pick up a thin and almost unnoticeable sun crust.  Deep snow can be found in protected areas that have not seen the effects of the wind. We saw a little bit of natural avalanche activity earlier this week when wind slabs were created on high terrain see the observation from near Duck Lake on NYE.  In addition, we did a short video in one of our pits on Wednesday of the PWL buried surface hoar layer failing in a PST.

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 21 deg. F.
Max. temperature in the last 24 hours: 21 deg. F.
Average wind direction during the last 24 hours: SSE
Average wind speed during the last 24 hours: 7 mph
Maximum wind gust in the last 24 hours: 18 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: NA inches

.SHORT TERM...Today through Sunday...Southwest flow aloft will
increase through Saturday ahead of an incoming trough. Some
mountains snow showers north of Baker and McCall are not out of
the question, but otherwise dry in this flow. Breezy southeast
winds in the Snake River Plain in response to the approaching
system, which also help to continue slow warming trend. By
Saturday evening, moisture and upper level winds increase
dramatically as a shortwave trough moves across the area from the
southwest. Should see significant snowfall on southwest facing
slopes late Saturday night through midday Sunday. Snow level
should be roughly in the 3000-4000 foot range. The main populated
areas of the Treasure, Magic, and Baker valleys likely to remain
dry through most of this, with dry air at the surface and
downslope shadowing in the southwest flow. Around 2-4 inches of
snow possible through this period in the mountain valleys around
McCall and Lowman, with higher amounts over the surrounding
mountains. There should be a brief lull in precip activity Sunday
afternoon ahead of the next system approaching the area for Sunday

.LONG TERM...Sunday night through Wednesday...The next push of
moisture enters the area Sunday night, with snow levels around
2000-3000 feet. Mid-level southwest winds will be particularly
strong with this feature which should keep most precipitation
limited to the higher terrain, initially. As flow decreases and
becomes more westerly on Monday, snow levels will gradually rise
to 3500-4500 feet. As a result, previously downsloped valleys will
have a better chance at seeing light precipitation by Monday
afternoon. Temperatures will rapidly become milder on Tuesday as a
strong warm front pushes into the area from the southwest. Snow
levels are forecast to rise above 6500-7500 feet by Tuesday
afternoon, allowing the potential for rain or rain/snow mix on
existing snowpack.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: Mostly cloudy, with a high near 31. Light south southeast wind. Mostly cloudy, with a low around 16. Calm wind. Partly sunny, with a high near 33. Light southeast wind
Temperatures: 31 deg. F. 16 deg. F. 33 deg. F.
Wind direction: SSE Calm SE
Wind speed: Light Calm Light
Expected snowfall: 0 in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: Mostly cloudy, with a high near 25. South wind around 10 mph. Mostly cloudy, with a low around 16. South southeast wind around 8 mph. Partly sunny, with a high near 26. South wind 8 to 13 mph.
Temperatures: 25 deg. F. 16 deg. F. 26 deg. F.
Wind direction: S SSE S
Wind speed: 10 8 8-13
Expected snowfall: 0 in. 0 in. 0 in.

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.