Avalanche Advisory published on February 8, 2019 @ 7:04 am
Issued by Dave Bingaman - Payette Avalanche Center
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The Avalanche Hazard is Moderate today.  Human triggered avalanches are possible today near ridgetops where isolated wind slabs exist.  It is also possible to trigger soft slabs in the upper 2 feet of the snowpack.  The most important factor to consider is the arrival of the next storm later today.  12+ inches will fall on Near Surface Facets and Surface Hoar on some slopes.  Expect the hazard to increase as we add more snow into the equation through the weekend.

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 ?
    Very Likely
  • Size ?
    Very Large

It is still possible to trigger an isolated wind slab left behind by the strong winds earlier this week.  Natural and human caused avalanches occurred earlier this week. Some of these slabs are resting on crusts or buried weak layers and have been camouflaged by the light accumulations we received all week.   Pay attention to wind stiffened snow that makes for shallow skiing or easy climbing on skis and sleds near ridgelines,  also watch for visual clues like wind ripples or shallow, dune-like formations where the wind has left its mark.

The next storm is supposed to come in without significant winds but bear in mind that with light density snow, it does not take much wind to transport it. Watch for new wind slabs forming on the north half of the compass over the next few days.





Avalanche Problem 2: Storm Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

The snow we received over the previous week has stabilized fairly quickly in most places. Pit tests show failure planes in the top 2 feet of the snowpack that are resting on density changes and grauple layers mid storm or weak layers that were the old snow surface prior to the 20+ inches of new snow we got.  For the most part these layers have lacked cohesion and the ability to propagate.  Skiing and riding in this new snow has been as good as it gets(sorry if you missed it).  The good and bad part of the story is that we are forecasted to receive another significant storm cycle beginning later today.  Be aware that this new snow will be falling on a fresh crop of Surface Hoar and Near Surface Faceted snow( recycled powder) on quite a few slopes.  Sluffing or dry, loose avalanches is also a consideration on steeper slopes.  As we add more light density snow on what is already there, sluffing will increase in size and its ability to travel.

As the new snow accumulates over the next few days put your free for all goggles back in the bag and bust out the avalanche goggles to keep you safe. Practice safe riding and skiing, check your beacon batteries and keep your eyes on your partners.

advisory discussion

PAC will issue 3 Advisories per week through the remainder of the winter as long as funding is available.

Please be aware that there are areas that are CLOSED to motorized traffic in the McCall, Goose Lake and greater West Mountains area.  Just because there are tracks in some areas, does not mean they are open.  Please respect all users and closures.  See the Payette Winter Travel Maps for clarification.  Both the East and West maps can be downloaded on the Avenza app on your phone or are available at trailheads and local shops.   IT IS YOUR RESPONSIBILITY TO KNOW WHERE YOU ARE AND WHERE THESE CLOSURES EXIST.  

recent observations

Several natural and human caused avalanches occurred earlier this week in the new and wind deposited snow.   Here is the most recent observation from the backside of Jug yesterday. 

Throughout the week, we observed and had similar reports of  widespread Surface Hoar and Near Surface Facets growing as the new snow dried out and cold temperatures dominated.  These layers will be a concern as we add more snow on top of them over the next few days.  Upper elevation ridges also had a variety of wind slab and wind crusts that formed throughout the week.  Some of these were reactive to skis and sleds as we traveled near ridgetops and on the most exposed terrain but disappeared once we got onto more wind protected slopes.

Here is a profile that we gathered yesterday on a ESE slope near 7700ft.  It shows a rightside up snowpack with some shallow, unconsolidated instabilities lacking propagation potential near the top.  The layer of concern was at the old/new snow interface near 60cm down.  It has shown hard propagation potential for the last few days but continues to be a concern worth noting.

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 3 deg. F.
Max. temperature in the last 24 hours: deg. F.
Average wind direction during the last 24 hours: 14
Average wind speed during the last 24 hours: 1 mph
Maximum wind gust in the last 24 hours: 12 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: NA inches

SHORT TERM...Today through Sunday...A strong winter system
is slated to begin moving into eastern Oregon this afternoon. As
moisture spreads eastward today, it will increase in intensity and
coverage with significant snowfall by this evening for portions of
southeast Oregon and into the central Idaho mountains. Moderate
to heavy snow will impact these areas through Sunday afternoon,
with Winter Storm Warnings in effect for portions of Oregon and
into the Upper Weiser River in Idaho. Additional Winter Weather
Advisories are in place for the West Central and Boise Mountains
and Southwest Highlands in Idaho, along with the Lower Treasure
Valley extending into Oregon. Snowfall is expected to impact
travel across the areas with snow packed and slick roads expected.
Further details regarding amounts of timing of the heaviest snow
can be seen in our winter hazard product (WSWBOI). Other areas
will still see snowfall from this system with areas outside the
hazards seeing 1 to 4 inches of snowfall from Friday evening
through Sunday afternoon. Gusty winds across the area on Sunday
afternoon could result in periods of blowing snow. Models continue
to show decent instability Sunday afternoon across eastern Oregon
and into portions of Idaho, with a few thunderstorms possible. Anyone
traveling this weekend is encouraged to check Oregon and/or Idaho
transportation websites for road conditions. Expect improving
conditions late Sunday afternoon through Sunday evening.

.LONG TERM...Sunday night through Friday...Cold and unsettled
weather continues through next week as several low pressure
systems cycle over the region. After one system exits to the east
Monday night, good model agreement shows another system sweeping
snow across the area Tuesday. The GFS shows a strong Pacific
moisture tap that lingers through next Friday with high PWAT
values to match, whereas the ECMWF is not as eager with moisture
of the passing systems. A blend of both models with the NBM and
climo was used for PoPs to mitigate model differences. Widespread
snow showers linger through Friday as temperatures remain below
normal through the period.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: A 40 percent chance of snow after 11am. Mostly cloudy, with a high near 22. Calm wind becoming south southwest around 6 mph in the afternoon. Total daytime snow accumulation of less than one inch possible. Snow. Low around 18. Southeast wind 3 to 7 mph. Chance of precipitation is 90%. New snow accumulation of 2 to 4 inches possible. Snow before 11am, then snow showers after 11am. High near 27. Southeast wind 5 to 8 mph. Chance of precipitation is 90%. New snow accumulation of 2 to 4 inches possible.
Temperatures: 22 deg. F. 18 deg. F. 27 deg. F.
Wind direction: SSE SE SE
Wind speed: 6 3-7 5-8
Expected snowfall: Trace in. 2-4 in. 2-4 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: Snow likely, mainly after 11am. Mostly cloudy, with a high near 13. Wind chill values between -10 and zero. South wind 7 to 9 mph. Chance of precipitation is 60%. Total daytime snow accumulation of 1 to 3 inches possible. Snow. Low around 10. Wind chill values between -3 and 2. South wind 9 to 11 mph. Chance of precipitation is 90%. New snow accumulation of 5 to 9 inches possible Snow before 11am, then snow showers after 11am. High near 16. Wind chill values between -1 and 4. South southeast wind 11 to 16 mph. Chance of precipitation is 90%. New snow accumulation of 4 to 8 inches possible
Temperatures: 13 deg. F. 10 deg. F. 16 deg. F.
Wind direction: S S SSE
Wind speed: 7-9 9-11 11-16
Expected snowfall: 1-3 in. 5-9 in. 4-8 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.