THIS AVALANCHE ADVISORY EXPIRED ON December 28, 2019 @ 7:33 am
Avalanche Advisory published on December 27, 2019 @ 7:33 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

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 the weight of a skier or snowmobile.  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.

Yesterday in the backcountry north of Tamarack Resort.  I was able to locate 2 separate SH layers in the mid to upper portion of the snowpack as well as a variation of the deeper problem that was more reactive than the surface hoar layers. Above the early November crust near 100cm is a layer of small grained facets that was failing in my pit tests.  This layer failed on isolation once. then provided several hard to initiate failures that showed energetic propagation that left behind a very planar surface.  Translation: hard to start avalanche but easy propagation under about 3 feet of denser slab above.  In many areas we have visited this winter,  this crust is decomposing and not providing the slick facet covered bed surface that I found yesterday in the West Mountain snowpack.

Without new snow in the future and with cold temperatures for the next few days,  the snow pack is going to struggle to gain strength anytime soon.   In some wind loaded areas, the scales tipped and the surface hoar failed during the storm or as it was further loaded last Friday.  In other more protected areas, it is still intact.  In addition, a new layer of Surface Hoar has begun building over the last several nights. 

The take home message is that we are still dealing with a relatively shallow and complex snowpack that is going to be changing for the worse as cold temperatures alter the structure.  Variability is high in a shallow snowpack and you're decision making and route selections need to reflect the variations that you will encounter.

Avalanche Problem 2: Wind Slab
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Stubborn wind slabs are still a problem in exposed areas and near our ridgetops.  I experienced cracking and localized collapsing of the wind slabs on shallow scoured areas yesterday and there are quite a few large and dense wind deposited features on the upper portion of our leeward slopes.  This problem should continue to diminish as cold temps decompose the snow surface.

recent observations

Touring out of bounds at Tamarack is always an eye opener. The tracks, traverses and generally poor decision making is evident on every steep pitch.  For the conditions we have been experiencing I am amazed that no one has gotten into trouble...  especially after having a couple of near misses out of bounds this week near Brundage.  Without preaching, I would just say that the FPAC is offering a variety of classes over the next month at both Tamarack and Brundage Resorts.  If you are a resort skier that is poking into the out of bounds terrain, take a class, get some knowledge. There are also several Level 1 classes that are available locally as well.

See our education page for more info:  http://payetteavalanche.org/events

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 10 deg. F.
Max. temperature in the last 24 hours: 14 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 4 mph
Maximum wind gust in the last 24 hours: 13 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: NA inches
weather

.SHORT TERM...Low clouds not quite as extensive as in the
last few days. As a result fewer flurries in the valleys,
and colder where partial clearing has occurred. Fairfield/
ID has been -8F this night vs a low of +2F last night.
Short wave trough will pass through today and should break
up the low clouds even more. The trough will bring
scattered snow showers to northern mountains. The Magic
Valley may get flurries later today. Upslope flow will
cause more significant snow showers in the southern
Sawtooths tonight and Saturday with an inch or two
accumulation possible. Tonight will be colder under strong
northerly flow aloft with a surface high building over
central idaho. Higher basins in Idaho where skies clear
above snow cover will become especially cold. Saturday
looks dry and cold. A Pacific warm front will bring a
chance of light snow Saturday night. Short wave ridging
will bring partial clearing Sunday morning and milder temps.
Next major Pacific storm will track south down the coast,
passing close enough for a chance of light snow in eastern
Oregon late Sunday and Sunday night. High pressure aloft
Monday will bring dry weather and normal temps.

.LONG TERM...Tuesday through Friday...A ridge will bring dry
conditions Tuesday before moisture from the northwest begins to
spill over the ridge into our region on Wednesday. Snow is
expected across most valley locations on Thursday before snow
levels begin to rise and temperatures warm Friday.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: Isolated snow showers. Mostly cloudy, with a high near 22. Calm wind becoming southwest around 5 mph in the afternoon. Chance of precipitation is 20% A 20 percent chance of snow showers before 11pm. Mostly cloudy, with a low around 13. Light and variable wind. Mostly sunny, with a high near 25. Light and variable wind.
Temperatures: 22 deg. F. 13 deg. F. 25 deg. F.
Wind direction: Calm Variable Variable
Wind speed: Calm Light Light
Expected snowfall: Trace in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: Scattered snow showers, mainly after 11am. Mostly cloudy, with a high near 16. South wind 7 to 9 mph. Chance of precipitation is 30%. Total daytime snow accumulation of less than one inch possible. A 30 percent chance of snow showers before 11pm. Mostly cloudy, with a low around 10. Wind chill values between zero and 5. Light and variable wind becoming north northeast 5 to 7 mph after midnight. New snow accumulation of less than a half inch possible. Mostly sunny, with a high near 19. Wind chill values between zero and 10. North wind 5 to 8 mph becoming light and variable.
Temperatures: 16 deg. F. 10 deg. F. 19 deg. F.
Wind direction: S NNE N
Wind speed: 7-9 5-7 5-8
Expected snowfall: Trace in. Trace in. 0 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.