THIS AVALANCHE ADVISORY EXPIRED ON December 29, 2019 @ 7:17 am
Avalanche Advisory published on December 28, 2019 @ 7:17 am
Issued by Dave Bingaman - Payette Avalanche Center
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Human triggered avalanches remain possible.  During the last week, skiers have triggered avalanches on multiple aspects.  You are most likely to trigger avalanches on wind loaded or wind protected slopes where surface hoar is still intact or where the snowpack is shallow and basal facets are still reactive to human triggers.  New soft storm slabs are building and should be expected on all steep slopes. Our snowpack is complex and variable and your decision making should reflect the conditions.

How to read the advisory


  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Persistent Slab
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Our major concerns continue to be the persistence of a layer of buried surface hoar mid pack and the basal facets at the bottom of our local snow pack.  Last weekend's warm up and the wind over the last weak has helped to consolidate the upper snowpack and begun to ease our concerns about the Surface Hoar somewhat, but both the surface hoar and the deeper basal facet/depth hoar layers are still intact and are still reactive in some places and should be in the back of your mind as you travel through the backcountry.  The development of a layer of faceted snow sitting above an old crust about 30cm/12in above the ground is worth noting,  it is becoming more reactive and showing a potential to fail where the crust is still intact.  A fresh layer of facets and surface hoar has been able to grow over the last few days as well and is slowly getting buried below the new fluff that is beginning to accumulate.

It is easy to get complacent about a persistent avalanche problem but it should be in the back of your mind as you travel right now,  The presence of these layers is enough to keep most seasoned backcountry travelers on lower angle slopes and away from committing terrain.  Persistent weak layers are unpredictable based on variations in the terrain and snowpack, they can also fail in unpredictable ways across a slope sometimes weeks after being buried.   

The photos below are all from the last 7 days and show a common theme in both the northern and southern parts of the valley.

 

 

Avalanche Problem 2: Loose Dry
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A new conditon is developing as the super low density snow we have been getting starts to accumulate, very soft wind slabs or loose, dry avalanches are increasing in both size and likelihood.  The wind increased over night and will increase this problem over the next few days as we continue to see an inch or two per day of this blower powder.  Wind can quickly turn a few inches of light snow into a 1-2 foot thick wind slab.  You should be aware of this potential on any slope that has seen even light winds over the last 24 hours.  We found these soft slabs forming on steep rollovers yesterday well below the ridgetops.

advisory discussion

FPAC is hosting a bunch of avalanche awareness classes in January including a women's only class.  Check out our Education page here.

recent observations

Reports from around the region are pretty similar, improving conditions with suspicious snowpack structure.  Over the last few days, our buried surface hoar has become less of an issue but the cold temps have allowed a fresh crop of facets and surface hoar to grow.  This layer is getting buried now under the cold, blower snow we have been adding over the last few days and will continue to build in slow, light weight increments.  Pay attention to how this new fluff is sticking to the snow below and how deep it is accumulating as it is already showing signs of instability on steeper slopes.

The persistent slab problem we have right now is pretty typical for an early season snowpack and really can provide a false sense of security.  The layers we have are widespread from the Wallowas across the PAC advisory area and into the Sawtooths and Boise Mountains to our south and east.  These layers once buried are notorious for remaining inactive until a substantial weather event triggers them or we step or ride on a trigger point. That being said, skiing and riding conditions are improving and luring folks into bigger terrain.  Your best and safest choice is still to stick to lower angle terrain and ride or ski one at a time. Keep your eyes on your partners from a safe spot.   Also, look at the slopes around you, persistent slabs often travel over large distances when they fail, it may be possible to trigger an avalanche on a slope above you or adjacent to the slope you are on. 

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 11 deg. F.
Max. temperature in the last 24 hours: 13 deg. F.
Average wind direction during the last 24 hours: W
Average wind speed during the last 24 hours: 4 mph
Maximum wind gust in the last 24 hours: 21 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: NA inches
weather

.SHORT TERM...Today through Tuesday...Low clouds and fog are
currently less extensive than the past few nights and temps
are generally colder early this morning. Weak Pacific frontal
system will come in tonight even through a short wave ridge
aloft. Front will bring a little snow to eastern Oregon
overnight. Models differ Sunday with GFS developing more
snow from this system while NBM keeps it weak. GFS has been
trending PoPs upward for several runs now and is preferred for
this forecast. Therefore light snow will be forecast for
Sunday, with accumulations generally less than one inch.
Temperatures will be milder tonight and Sunday due to clouds
and pcpn. Strong Pacific storm will head southward down the
coast passing closest to our area on Sunday but with only
minimum effect on our CWA. Upper ridge will come in from the
north Monday behind the southward moving Pacific storm. The
ridge should keep our area dry with normal temps late Sunday
night through Tuesday.

.LONG TERM...Tuesday night through Friday...Turning colder at
the end of next week as a pattern change brings cold unsettled
conditions. An upper level ridge will weaken over the area and
moist zonal flow will bring snow showers to the region on
Wednesday into Thursday. Snow showers will continue over the
mountains before warmer air begins to raise snow levels to
around 4000ft MSL by Thursday afternoon. Thursday will be the
warmest day of the period with temperatures in the 40s in the
valleys. Unsettled conditions will continue ahead of a strong
cold front which will arrive on Friday afternoon. Snow levels
with this cold front will lower to the valley floors with colder
unsettled conditions expected for the weekend. Temperatures
will be slightly above normal Wednesday through Friday, but
below normal for next week.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: Mostly sunny, with a high near 26. Calm wind. A 20 percent chance of snow after 11pm. Mostly cloudy, with a low around 16. Calm wind. A 50 percent chance of snow. Cloudy, with a high near 28. Calm wind. New snow accumulation of less than a half inch possible.
Temperatures: 26 deg. F. 16 deg. F. 28 deg. F.
Wind direction: Calm Calm Calm
Wind speed: Calm Calm Calm
Expected snowfall: Trace in. Trace in. Trace in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: Mostly sunny, with a high near 19. Wind chill values between -2 and 8. North wind 5 to 9 mph becoming light north northwest in the afternoon. A 30 percent chance of snow after 11pm. Mostly cloudy, with a low around 15. Light and variable wind becoming south around 5 mph after midnight. New snow accumulation of less than a half inch possible. A 50 percent chance of snow. Cloudy, with a high near 22. South southwest wind 5 to 7 mph. New snow accumulation of less than a half inch possible.
Temperatures: 19 deg. F. 15 deg. F. 22 deg. F.
Wind direction: N Variable SSW
Wind speed: 5-9 Light 5-7
Expected snowfall: Trace in. Trace in. Trace 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.