THIS AVALANCHE ADVISORY EXPIRED ON January 1, 2018 @ 6:48 am
Avalanche Advisory published on December 31, 2017 @ 6:48 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The primary avalanche problem today is wind slabs on exposed ridges and upper elevation slopes. Recent weather has stiffened the upper snowpack. Variability is the name of the game with significant changes found on different aspects.  Multiple weak layers exist in the upper snowpack and are just starting to become reactive as the snow adjusts to these changes.  Continue to use cautious route selection, careful snowpack evaluation, and good travel protocols.

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

We observed wind slabs on exposed ridges yesterday on a ski tour near Sgts, North of Brundage. Wind slabs are resting on a variety of weaker layers below and have been reactive to ski cuts and in our pits.

The bottom line right now is variability, poor snowpack structure still exists at the bottom of the snowpack on multiple aspects.  Changes are occurring in the snowpack as well,  lower elevation slopes took a beating with temperatures over freezing and a period of rain or very wet snow. Pay attention to these changing conditions as you change slopes and aspects today and over the next few days,  take the time to feel the snow as you travel and look for obvious visual clues of wind impact.  Notice how far you are sinking into the snowpack, if you are deep in the fluff and suddenly find yourself traveling more shallow, see cracking or rippled, drifted or textured snow, you are most likely on a wind slab.  The worst case scenario right now would be the possibility that triggering one of these relatively small winds slabs could affect some of the deeper weak layers below resulting in a larger avalanche and higher consequences.

 

Avalanche Problem 2: Normal Caution
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely

With the lack of a decent dump of snow in the last week, we have not added much in the form of a  slab since last weekend's storm cycle, but light dustings in the valley and mountains have added a few additional inches to the upper elevation snowpack. Upper elevation temperatures have been consolidating the upper snowpack which may eventually help form a slab...given the variability, and the nature of this problem we will be monitoring the upper snowpack slab formation potential.

Changes are likely with shifting winds impacting exposed upper elevation slopes which means you need to be diligent in your slope choices if you are skiing or riding in steeper terrain.  The wind slab problem described above is going to be your primary hazard and we by no means know how widespread it is right now so be aware of potential changes in the snowpack as you change aspects throughout the day.

advisory discussion

Great News:  the Granite Mt. weather station is online.  Go to the weather page and click the link for a table of conditions at 7700 ft.

Bad News: The PAC will only be operating 3 days per week this year.  Your observations are more important now than ever before, please let us know what you are seeing while you are out riding or skiing in the local backcountry.  It's super easy to send us info and photos with date, location, pictures, general or specific snow observations, just click on the submit observations page on the PAC website and add what you saw or found in the snow.  You can also email the forecasters directly at:  forecast@payetteavalanche.org

recent observations

We traveled through some nasty lower elevation slope in Lick Creek yesterday in search of deep snow in the upper elevations.  On our way up to 8302 and the Gunsight Ridge we found a variety of conditions;  lower elevation slopes were shallow, wet and punchy as the snow collapsed around logs, rocks and other hollow spots.  Upper elevation slopes provided a great look at multiple conditions and some evolving wind slab problems.  See the pit photos above and  realize that these very different conditions were found only 500 feet apart. Great skiing was found on Northerly slopes down to about 6800 feet, below that the buried obstacles kept us on our toes.

 

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 22 deg. F.
Max. temperature in the last 24 hours: 28 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 13 mph
Maximum wind gust in the last 24 hours: 27 mph
New snowfall in the last 24 hours: 4 inches
Total snow depth: 64 inches
weather

.SHORT TERM...Today through Monday...Dry conditions under a
northwest flow aloft will maintain cool temperatures across the
region through the day today. Early morning patchy fog that
develops overnight will burn off before noon, but should redevelop
more widely early Monday as an upper ridge moves over the region.
As warm air streams in aloft with the ridge, inversion conditions
will redevelop in the valleys with temperatures there trending
colder Monday and mountain temperatures trending warmer.

.LONG TERM...Monday night through Sunday...A ridge axis will build
to our west and move through the area between Monday night and
Thursday. This will help intensify an inversion in the valleys, and
therefore keep the valleys cold while the mid and upper elevations
warm slightly. As the upper level ridge axis moves to our east,
moisture and a chance of precipitation will move in from the west.
With cold air trapped in place in the valleys, this will bring a
chance of freezing rain to different parts of the area from Wed
night through Saturday night. This does not mean that a location
will see a three-day freezing rain event. It means that conditions
will make it possible for freezing rain in varying locations within
that time frame. As we get nearer in time, we will be able to better
delineate the most likely areas and become more specific in the
forecast. By next weekend, it appears we will see a shift to a more
progressive pattern.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Sunday Sunday Night Monday
Weather: Patchy fog before 11am. Otherwise, sunny, with a high near 27. East northeast wind around 5 mph becoming calm. Patchy fog after 11pm. Otherwise, mostly clear, with a low around 10. Light south southeast wind. Mostly sunny, with a high near 26. South wind around 5 mph becoming calm in the afternoon.
Temperatures: 27 deg. F. 10 deg. F. 24 deg. F.
Wind direction: E/NE SE S
Wind speed: 5 mph-calm Light 5 mph-calm
Expected snowfall: Trace in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Sunday Sunday Night Monday
Weather: Sunny, with a high near 25. Calm wind becoming south 5 to 9 mph in the morning. Mostly clear, with a low around 18. South southwest wind 9 to 13 mph. Mostly sunny, with a high near 32. West southwest wind 7 to 9 mph.
Temperatures: 25 deg. F. 18 deg. F. 32 deg. F.
Wind direction: S S/SW W/SW
Wind speed: 5-9 mph 9-13 mph 7-9 mph
Expected snowfall: 0 in. 0 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.