THIS AVALANCHE ADVISORY EXPIRED ON December 31, 2017 @ 7:50 am
Avalanche Advisory published on December 30, 2017 @ 7:50 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The primary avalanche concern today is wind slabs on exposed ridges and upper elevation slopes.  Yesterday's weather stiffened the upper snowpack into a 8-12 inch cohesive slab in many areas. 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.   Cautious route selection, snowpack evaluation and good travel protocols are a must today.

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

Yesterday's storm may have fizzled but SSW winds were steady throughout the day and increased last night with a shift to the  W and gusts near 30 mph.  We observed wind slabs forming on exposed ridges yesterday near 7600 feet and above.  The 6-12 inch slab that was created is resting on a variety of weaker layers below and was becoming reactive to ski cuts and in our pit on a ESE ridge provide some easy failures in shear and compression and propagated easily with a very low ECT score.  Another pit (500 feet each other) on the opposite side of the same ridge facing NNW showed a surprisingly deep snowpack with an unconsolidated storm slab  and no propagation potential in the upper snowpack.  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 falling yesterday morning.  Upper elevation slopes remained relatively cool and took a beating from the winds.  Wind's today are expected to shift to the NNW as a cold front approaches and will further impact the upper elevation slopes before calming down this afternoon.  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: Storm Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Unfortunately, we have not added much in the form of storm 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  over the last few days, mostly in the northern portions of the advisory area.  Upper elevation temperatures have kept the new storm snow light and unconsolidated for the most part which has kept our avalanche hazard fairly low on protected slopes.  Yesterday was one of the warmest days we have had and we experienced several rounds of medium to high intensity snowfall. Skiing was outstanding on the northerly slopes yesterday and we found a surprisingly deep snowpack near 7500 feet and above.  Changes are likely with shifting winds impacting exposed upper elevation slopes yesterday and today 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 Sunday...A weak cold front is
currently working its way through the region and looks to be
draped southwest to northeast across southeast Oregon as of 3 AM
MST. Models have been bullish with precipitation amounts leading
up to this event but don`t seem to be panning out this morning, so
have lessened amounts across the region. The biggest challenge in
this morning`s forecast is where we will receive freezing rain as
there is ample warm air aloft. With temperatures above freezing
being reported at the Boise Airport, Mountain Home and east
through the Magic Valley, current thinking is that any freezing
rain will not be widespread in these areas, rather, it will be
isolated if at all. However, Canyon County and west through the
Treasure Valley are still sitting below freezing and will maintain
their freezing rain threat through the morning. A Winter Weather
Advisory was issued Friday evening for this threat and will be
continued this morning.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: A 30 percent chance of snow before 11am. Mostly sunny, with a high near 29. West southwest wind 6 to 9 mph. Total daytime snow accumulation of less than a half inch possible. Patchy fog after 11pm. Otherwise, mostly clear, with a low around 7. Light and variable wind. Patchy fog before 11am. Otherwise, sunny, with a high near 24. Wind chill values between zero and 10. Light and variable wind becoming south southwest around 5 mph in the afternoon.
Temperatures: 29 deg. F. 7 deg. F. 24 deg. F.
Wind direction: W/SW Variable S/SW
Wind speed: 6-9 Light Light
Expected snowfall: Trace in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: A chance of snow before 11am, then scattered snow showers after 11am. Partly sunny, with a temperature falling to around 18 by 5pm. West wind 8 to 18 mph. Chance of precipitation is 50%. Total daytime snow accumulation of 1 to 2 inches possible. Isolated snow showers before 11pm. Partly cloudy, with a low around 14. West wind 3 to 7 mph. Chance of precipitation is 20%. Sunny, with a high near 24. South southwest wind 6 to 10 mph.
Temperatures: Falling to 18 by 5pm deg. F. 14 deg. F. 24 deg. F.
Wind direction: W W S/SW
Wind speed: 8-18 3-7 6-10
Expected snowfall: 1-2 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.