THIS AVALANCHE ADVISORY EXPIRED ON December 30, 2018 @ 7:01 am
Avalanche Advisory published on December 29, 2018 @ 7:01 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

 Moderate Avalanche hazard exists throughout the West Central Mountains.  The snowpack is widely variable right now.  Wind Slabs may be found in wind exposed, upper elevation terrain.  Human triggered avalanches are also possible in wind protected areas where buried weak layers exist within the snowpack.  Your safest option is to avoid steep terrain, especially areas where the snowpack 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 ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

The combination of light, dry snow and winds from multiple directions  over the last few days has been perfect for creating soft, thin wind slabs on upper elevation, wind exposed slopes.  These slabs may be found on all slopes that have seen winds over the last week.  These relatively thin slabs also have the possibility of triggering or "stepping down" into  the deeper weak layers within the snowpack.   Expect to see increasing wind loading and slab development beginning tonight and increasing Sunday as winds increase with another storm system entering our area.

Wind slabs are relatively easy to spot and recognize, look for cornices and drifted pillows of snow, or areas where the snowpack is more firm and supportive to the weight of a skier or snowmobiler.  

Avalanche Problem 2: Persistent Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Our snowpack continues to show us reasons not to venture into steep terrain right now.  Despite the fact that we have not seen any new avalanches throughout the local mountains in almost 2 weeks, we still have a VERY unusual and atypical snowpack for the West Central Mountains.  Avalanche Professionals to our East and West are echoing the same themes in both the Sawtooth area and in the Wallowas.  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. 

In many areas, the snowpack is still relatively thin and the lack of snowpack is allowing skiers and snowmobilers to affect this layer resulting in collapsing or whumphing as this layer fails or is triggered by our weight.  We experienced several of these yesterday in wind protected areas including one that displaced the snow in the flats, reverberated away from us for several hundred feet and shook snow out of nearby trees.

The skiing and riding is getting better by the day with the addition of light, dry snow but unfortunately, until we have a large snowfall event coupled with warmer temperatures our buried weak layers are going to be a problem.  Your best and safest bet is to avoid slopes steep enough to produce avalanches, especially where the snowpack is still thin and the weak layers are more likely to be influenced by your weight.

Variability is the name of the game right now, check out the pictures and pit profiles from our day out yesterday in the observations section of the advisory or on the observations page.

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.

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 link and 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

The skiing and riding continues to get better, you  really couldn't ask for better quality snow and the almost daily refresher of an inch or two of new snow has done a great job keeping it soft out there.   There is still a lot of buried treasure, especially for sleds. Watch your a arms and your bases but enjoy it while it is here.  

These two pits were on the same ridgeline about 300 vertical feet apart in elevation.  The upper pit showed a much denser and slightly deeper snowpack where the weak layers were much less reactive in our tests.  The lower pit showed hard to initiate failures but easy propagation on both of the buried weak layers in a more shallow snowpack.  The profile shows the hardness of the snowpack from the top down in the shaded blocks, they both show the problem we have been discussing:  more firm snow over weaker snow below. 

We also were able to trigger several localized collapses and one very widespread collapse in the protected terrain near the toe of this slope.   In addition, both pits were dug on slopes less than 30 degrees. 

 

 

 

 

 

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 12 deg. F.
Max. temperature in the last 24 hours: 17 deg. F.
Average wind direction during the last 24 hours: N
Average wind speed during the last 24 hours: 8 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 Monday...Light snow will continue to
spread into the area as moisture arrives from the northwest.
There have already been some light accumulations across the north,
including Burns, Baker City, and McCall. Additional accumulations
will be light, with an inch or two expected in the northern
mountains and less than an inch in the valleys. The snow will
decrease this afternoon, although it will persist in the northern
mountains. Little additional accumulation is expected.
Precipitation will spread back into the area tonight as an upper
trough moves into the northern Rockies. Snow levels will rise to
around 3500 feet ahead of a cold front, resulting in rain and snow
for the lower valleys. Several inches of new snowfall are expected
in the higher elevations across the north, including the
mountains in Baker County and in the Boise/West Central Mountains.
The precipitation will taper off to showers behind a cold front on
Sunday. Additional light accumulations are possible in the higher
elevations. Winds will increase with the arrival of the cold
front, especially east of Mountain Home where it will be very
windy Sunday afternoon. The wind and showers will diminish Sunday
night as a drier northerly flow aloft develops behind the exiting
trough. The drier conditions will continue through Monday.
Temperatures will trend warmer through Sunday, then colder on
Monday.

.LONG TERM...Monday night through Saturday...The extended will
start off with a good northerly flow from northern Canada as a
cutoff low drops into the desert southwest Tuesday. This brings a
fairly strong sfc high of 1040mb into eastern Idaho. Tuesday
morning will be very chilly across all locations as skies clear.
Otherwise good model consensus through most of the week. Models
keep the upper ridge off the west coast around 35N with the ridge
axis pushing NE into Oregon. This keeps the main jetstream
pushing mainly into British Columbia through Thursday. If there is
any threat of snow during the extended, it could be along the
Salmon River Thursday afternoon as the flow flattens slightly.

Temperatures are expected to remain at or slightly above normal
depending on the amount of mid and high clouds streaming
overhead. There still remains timing differences by the weekend
but all the models are indicating that another system pushes into
the Pac Nw Friday afternoon and begins to lift to the ENE. This
would favor a better threat of snow across Valley and Baker
counties than the Nv border region.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: Snow, mainly before 11am. High near 25. Light south wind. Chance of precipitation is 80%. Total daytime snow accumulation of less than one inch possible. Snow. Low around 25. Light south wind increasing to 5 to 10 mph in the evening. Chance of precipitation is 100%. New snow accumulation of 1 to 3 inches possible. Snow showers likely. Mostly cloudy, with a high near 29. South southwest wind 8 to 11 mph becoming west northwest in the morning. Chance of precipitation is 70%. New snow accumulation of around an inch possible.
Temperatures: 25 deg. F. 25 deg. F. 29 deg. F.
Wind direction: S S SSW then WNW
Wind speed: Light 5-10 8-11
Expected snowfall: 1 in. 1-3 in. 1 in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: Snow, mainly before 11am. High near 23. South southwest wind around 7 mph. Chance of precipitation is 90%. Total daytime snow accumulation of 1 to 2 inches possible. Snow. Low around 16. South southwest wind 9 to 17 mph. Chance of precipitation is 100%. New snow accumulation of 3 to 5 inches possible. Snow showers. Temperature falling to around 13 by 5pm. Wind chill values between -1 and 8. West southwest wind 11 to 16 mph becoming northwest in the morning. Chance of precipitation is 80%. New snow accumulation of 2 to 4 inches possible.
Temperatures: 23 deg. F. 16 deg. F. 13 deg. F.
Wind direction: SSW SSW WSW
Wind speed: 7 9-17 11-16
Expected snowfall: 1-2 in. 3-5 in. 2-4 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.  This advisory applies only to backcountry areas outside established ski area boundaries. and describes general avalanche conditions.  Local variations always occur. and should be expected. This advisory expires at midnight on the posted day unless otherwise noted