THIS AVALANCHE ADVISORY EXPIRED ON December 24, 2019 @ 6:58 am
Avalanche Advisory published on December 23, 2019 @ 6:58 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

Human triggered avalanches remain possible in wind loaded terrain.  The spring like temps over the last few days have helped our snowpack begin to heal but we are not out of the woods yet.  Observations from across the West Central Mountains show improving stability but concerns about structure and the persistent weak layers within the snowpack.  Make conservative choices in your route finding and avoid steep wind loaded terrain.

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 concern right now is the persistence of a layer of buried surface hoar in our local snowpack. Over the last few days the snowpack has begun to consolidate and heal this layer somewhat but both the surface hoar and the deeper basal facet/depth hoar layers are still intact and worth noting from a snowpack structure and stability testing viewpoint.  In addition, the surface hoar layer has been further stressed with the wind loading that occurred late last week during the Wednesday/Thursday storm.  In some wind loaded areas, the scales tipped and the surface hoar failed during the storm or as it was further loaded Friday.   In areas that did not fail naturally, this layer remains sensitive enough that a skier or snowmobiler could trigger an avalanche.   

I would consider the snowpack a WEAK moderate on the danger scale right now.  Stability is generally improving but structure is still variable and there are areas where you could trigger an avalanche in a wind slab or wind loaded area but the real problem is the ability of that avalanche to initiate and  propagate in the surface hoar and create a larger avalanche.  It is splitting hairs at this point to call our current problem more of a wind slab versus a persistent slab problem.  The wind slabs will continue to become less of a problem over the next few days but the combination of these two problems should make you wary in wind loaded terrain right now.

Avalanche Problem 2: Wind Slab
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Wind slabs were created during the last storm and continued to build through Friday.  While the winds are still  blowing, the amount of snow for transport is almost nil.  Scoured and wind sculpted windward slopes are the norm with some stiff, challenging snow to be found right now while the leeward slopes are still preserving good snow.  Close to the ridge tops, cornices have started to grow but stiff wind pillows grew quite a bit in some areas.  While these are exactly the areas that have the best snow for skiing and riding, these are also the areas that have wind slabs that are still sensitive enough to trigger and are most likely harboring the surface and depth hoar layers that we have been tracking.  We have had multiple reports of human and naturally caused avalanches in these areas over the last 3 days and the problem is compounded by the persistence of the weak layers below the recently deposited snow.  

recent observations

I took advantage of the nice day yesterday to tour out of bounds near Brundage Mt. Resort with my daughter and some friends.  It felt like April...temps in the 40's with some wind but lots of sun.  We found good skiing up high and a couple of notable recent avalanches.  One appeared to have run naturally during Thursday or Friday and the second one looked like it had been triggered by a skier on Saturday.  Both were in wind loaded areas and ran down to the buried surface hoar layer.  It was great to see these and to stop and talk about them with our next gen tourers and explain how avalanches are possible even days after a storm.  Observations from West Mountain near Tamarack Resort and Jughandle confirmed that these layers are widely distributed.  See the observations submitted for a description of those avalanches.  THANKS TO ALL OF THE FOLKS SUBMITTING GREAT OBS THIS YEAR!

Needless to say the sun and the temps put the whammy on the lower elevation snow...as we passed through about 6500 ft. the snow started getting sticky and heavy.  By the time we hit the exit on Sarge it was combat spring skiing.  If you are looking for soft snow over the next few days you are going to find it on protected northerly slopes and in exactly the same spots where the avalanche hazard is concentrated.  Avoid the wind stiffened slabs near the ridgetops and be aware that you may still be unlucky enough to trigger an avalanche in the surface hoar remotely or in areas beyond where you are traveling

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CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 24 deg. F.
Max. temperature in the last 24 hours: 36 deg. F.
Average wind direction during the last 24 hours: S
Average wind speed during the last 24 hours: 10 mph
Maximum wind gust in the last 24 hours: 35 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: NA inches
weather

.SHORT TERM...Today through Thursday...The northern push of
moisture from the split trough will impact the area today. High-
resolution models demonstrate the potential for some precipitation
to move into the Treasure Valley. Included some slight chance
wording to the forecast for the potential this morning. This
initial push of moisture will weaken this afternoon, though on its
heels will be the moisture from the southern chunk of the initial
trough. The second push continues to look more significant than
its predecessor, with moisture spreading across much of
southwestern Idaho by Tuesday morning. Snow levels keep a rain-
snow mix in most valleys with snow otherwise. The central Idaho
mountains are most favorable with this system, especially the
Boise Mountains. This system will progress eastward through the
day, with most moisture moving out of the area on Wednesday
evening. Around 2 to 5 inches of snowfall will be possible across
the Boise Mountains, with a few areas seeing amounts up to around
7 inches. Pockets of moisture on Wednesday will keep some
lingering activity, with little impact expected. Thursday looks
mostly dry as northwest flow works to move over the area. With the
systems early in the forecast period, expect cooling temperatures
through Thursday.

.LONG TERM...Thursday night through Monday...Models are all in
good agreement showing the elongated upper trough moving east out of
the region Friday morning. There could be a few lingering snow
showers across Idahos west central mountains, otherwise dry
conditions expected. Models all depict an upper ridge developing
over the region for the remainder of the extended period. Therefore
dry conditions with generally light winds and near normal
temperatures expected. Little confidence with the next potential
system that models showing pushing towards the coast by Monday as
they all show something different as it progresses east.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Monday Monday Night Tuesday
Weather: A 30 percent chance of snow, mainly before 11am. Mostly cloudy, with a high near 34. South southwest wind 3 to 5 mph. Total daytime snow accumulation of less than a half inch possible. A 30 percent chance of snow after 11pm. Mostly cloudy, with a low around 21. Calm wind. New snow accumulation of less than a half inch possible. Snow likely, mainly after 11am. Cloudy, with a high near 32. Light and variable wind. Chance of precipitation is 60%. New snow accumulation of less than a half inch possible.
Temperatures: 34 deg. F. 21 deg. F. 32 deg. F.
Wind direction: SSW Calm Light
Wind speed: 3-5 Calm Variable
Expected snowfall: Trace in. Trace in. Trace in.
Granite Mountain at 7700 feet.
  Monday Monday Night Tuesday
Weather: A 40 percent chance of snow. Mostly cloudy, with a high near 25. South wind 10 to 13 mph. Total daytime snow accumulation of less than one inch possible. A 30 percent chance of snow after 11pm. Mostly cloudy, with a low around 18. South wind around 6 mph becoming calm in the evening. New snow accumulation of less than a half inch possible. Snow likely, mainly after 11am. Mostly cloudy, with a high near 23. Calm wind becoming south southwest 5 to 7 mph in the afternoon. Chance of precipitation is 60%. New snow accumulation of less than one inch possible
Temperatures: 25 deg. F. 18 deg. F. 23 deg. F.
Wind direction: S S SSW
Wind speed: 10-13 6 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.