Avalanche Advisory published on January 7, 2019 @ 7:21 am
Issued by George Halcom - Payette Avalanche Center
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Considerable Avalanche hazard exists throughout the West Central Mountains.  Wind Slabs exist in exposed, upper elevation terrain, and have potential to "step down" into weak layers deeper in the snow pack.  Avalanches are also possible in wind protected areas where Storm Slabs have formed, and where buried weak layers exist.  Your safest option is to avoid steep, wind loaded terrain, and  areas where the snow pack is still thin enough to trigger the sugary, faceted layer near the ground.

How to read the advisory

  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

The last 24 hours have been windier than we would have ordered. Gusts upwards of 27 MPH were recorded at the weather station on Granite last night. Over the last week, wind slabs have formed on a variety of upper elevation slopes.  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: Storm Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

Yesterday, near Duck Lake we witnessed a small storm slab that had slid naturally on a steep, 40 degree North face during the storm. The new snow consists of a denser bottom or begining part of the storm was warmer and laid down denser snow, and showed moderate results in our test pits, and will take a bit to stabilize. Stay alert in steep areas protected from the wind where the denser slabs have built up during the storm and have not bonded to the older snow.




Avalanche Problem 3: Persistent Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

Our snowpack continues to gain strenght but still 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 propigation Saw test  that we did yesterday to test this layer, it showed ample ability to propagate if initiated, Enjoy.  The recent wind and snow 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.

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

Yesterday was a deep day in the mountains, and a very windy day to say the least. We saw moderate to strong winds out of the south, and nearly a foot of new snow. We observed a natural storm slab avalanche R1D1 on a North aspect near Duck Lake, Black Dog bowl on a North aspect about 40 degrees. Check out this video of yesterdays Propagation Saw Test video.

Above is a pit from Yesterday

We also witnessed another casualty of buried treasure: a sledder with one ski riding one side back to the parking lot. Be careful out there...there still are many things to run into.

The wind did a lot of damage last week on upper elevation exposed slopes. 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: 12 deg. F.
Max. temperature in the last 24 hours: 20 deg. F.
Average wind direction during the last 24 hours: W
Average wind speed during the last 24 hours: 7 mph
Maximum wind gust in the last 24 hours: 27 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: NA inches

Area Forecast Discussion
National Weather Service Boise ID
325 AM MST Mon Jan 7 2019

.SHORT TERM...Today through Wednesday...A cold front is working its way
across the area this morning. The latest observations indicate
the front is quickly moving eastward through southwest Idaho.
Winds have been gusty along and ahead of the front with values as
high as 30 mph in the Treasure Valley and 45 mph in the Magic
Valley. Expect these gusty winds to linger into the early morning
hours, especially in the Magic Valley. Precipitation has been
falling steadily across the mountains of eastern Oregon and
central Idaho. Snow has been prevalent above 3500 feet, and
webcams are showing snow covered roadways in most mountain areas.
Radar indicates the back edge of the precipitation is along the
front. The forward motion of the front will bring the
precipitation to an end for Oregon very early this morning and by
mid day for most Idaho areas. Treasure Valley locations in Idaho
will see mainly rainfall, with a brief change- over to snow
possible. Little accumulation is expected. Magic Valley locations
could see up to one inch of snowfall in total. Oregon locations
will see little additional accumulation.

Cooler air will pour in behind the front with temperatures
hovering near normal through mid week. High pressure is expected
to build in strongly through Wednesday, with increasing moisture
riding up and over the ridge each day. By Tuesday Night into
Wednesday the expectation is that enough moisture will arrive to
trigger shower activity over mainly eastern Oregon and the central
Mountains of Idaho.

.LONG TERM...Wednesday night through Sunday...Lingering snow
showers will continue over Wednesday night for the west-central
Idaho mountains as the trough over the region slowly lifts
northeastward. Snow levels will be relatively high at 4500-5500
feet MSL with only light additional snow accumulations expected.
Dry high pressure rapidly builds into the region Thursday and
Friday, allowing temperatures to remain several degrees above
normal. Have trended the forecast towards a drier solution for
Friday into Saturday with the latest GFS/ECMWF trends which keep
the high pressure pattern in place through Saturday.

Saturday night through Monday night...Breezy winds along with
increasing chances for unsettled weather are in store as the pattern
changes from dry ridging to moist troughing starting Sunday morning.
A mixture of snow and rain showers (snow alone in the high
mountains) will frequent the area as a series of trough-ridge
couplets transition through. Most areas in the Treasure Valley
should experience rain. Expect to see improving conditions to spread
eastward as a drier, more stable air mass starts to spill into the
area starting early Monday. High and low temperatures are expected
to measure in around 3 to 5 degrees above normal.


.AVIATION...MVFR/IFR with rain/snow through early morning, becoming VFR
generally after 07/15Z. Cold front exiting the area this morning
will keep winds elevated and lingering snow showers. Surface winds:
generally west or northwest 10-20 kts with gusts up 30 kts,
becoming 5-15 kts by late morning. Winds aloft near 10 KFT MSL:
west 25-35 kts.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Monday Monday Night Tuesday
Weather: Snow showers likely, mainly before 11am. Partly sunny, with a high near 26. South southwest wind around 7 mph. Chance of precipitation is 60%. Total daytime snow accumulation of less than a half inch possible. Partly cloudy, with a low around 12. Light east southeast wind. A 30 percent chance of snow, mainly after 11am. Mostly cloudy, with a high near 32. Light east southeast wind. New snow accumulation of less than a half inch possible.
Temperatures: 26 deg. F. 12 deg. F. 32 deg. F.
Wind direction: SSW SE ESE
Wind speed: 7 Light Light
Expected snowfall: less than one half in. 0 in. Less than one half in.
Granite Mountain at 7700 feet.
  Monday Monday Night Tuesday
Weather: Snow showers likely, mainly before 11am. Mostly cloudy, with a high near 17. Wind chill values between -2 and 4. Southwest wind 11 to 14 mph. Chance of precipitation is 60%. Total daytime snow accumulation of less than one inch possible Mostly cloudy, with a low around 11. Wind chill values between -1 and 4. South southeast wind around 9 mph. A 40 percent chance of snow, mainly after 11am. Mostly cloudy, with a high near 26. South wind 9 to 13 mph. New snow accumulation of less than a half inch possible.
Temperatures: 17 deg. F. 11 deg. F. 26 deg. F.
Wind direction: SW SSE S
Wind speed: 11-14 9 9-13
Expected snowfall: Less than one in. 0 in. Less than one half 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.