Avalanche Advisory published on January 25, 2020 @ 7:34 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The Avalanche Danger is MODERATE.  Natural avalanches are unlikely but human triggered avalanches remain possible.  Shallow wind and storm slabs are possible on leeward slopes.  You may also trigger avalanches on layers buried from 1 foot to several feet.  Our deep persistent layers are buried 6-9 feet deep but should still be in the  back of your mind as you choose steeper terrain.  Rain in the lower elevations may increase the potential for wet avalanches starting tonight and through Sunday.

How to read the advisory

  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Storm Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

Some wind transportation has occurred in the last 24 hours but the winds were not as strong as predicted yesterday.  Shallow wind slabs may form today near ridgelines.  There is also potential for shallow avalanches on instabilities in the upper 12-18  inches of the snowpack.  We found a layer of grauple yesterday as well as an old snow surface with rounding facets in the upper 2 feet of the snowpack that had some potential to fail but did not propagate in our tests.  Overall our snowpack is strengthening and consolidating and despite the warming trend providing plenty of soft snow for skiers and riders to enjoy.  

Pay attention to changing conditions as you change terrain.  There is still a fair amount of variability in the snowpack throughout the West Central Mountains and surrounding areas. It is still possible though not likely that you could trigger deeper avalanches in shallow, rocky terrain where early season weak layers are closer to the surface.  Rain and rising temperatures tonight and Sunday will increase the potential for wet avalanches especially in the lower elevations.

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

Our deep slab problem right now is the perfect definition of  a LOW PROBABILITY/HIGH CONSEQUENCE scenario.  The chance of triggering is low and becoming more and more isolated but still lingering.  Upper elevation slopes where early season snow was preserved is your likely best culprit.  Add uneven rocky terrain into the picture and you are increasing the chance of finding that landmine trigger point where the snow is more shallow and the weak layer is closer to the surface.  The size and density of the slab and the potential outcome of triggering one of these deep, persistent slabs is enough to keep savvy riders and skiers off of and away from the likely slopes.  These are the same layers that have been responsible for fatalities near the West Central Mountains and in several other areas this winter.  We also saw several large, natural avalanches last week that released in these layers, so under the right conditions large avalanches are still possible.

We have been finding a well preserved layer of surface hoar 5 feet down in the snow pack on high, north facing slopes.  In addition loose depth hoar and facets are still present in some areas above and below the November crust that is now buried 6-8 feet down.  We generally do not see problem layers like these persisting with a deep snow pack above them in this area.  Variability throughout the surrounding area means that you may be riding or skiing in an area with 8 feet of snow on one slope and half that much on a different one.   

The chance of rain in the lower elevations combined with heavy, wet snow and some wind loading is going to give these layers another test tomorrow.  Your best bet is to choose slopes with low consequences while the snowpack is adjusting to these changes. 

advisory discussion

*Snowmobiliers, the Granite Mountain closure went into effect on Janurary 15.  Please respect Brundage Catski terrain closures which are CLEARLY marked on the west side of Goose Lake.  There is a shared use route at the northern end of the closure to allow access to Granite Mt Lookout and the upper east face of Granite Mt.  There are also other areas that are closed to snowmobiling in the West Central Mountains. Click here for the Payette National Forest Winter Travel Map.

*Note to skiers accessing Jughandle Mountain from Silver Fox Trail.  Please park in signed areas only. Blocking or narrowing the road could result in loss of access to this area, ticketing or towing by Valley County.  There is NO parking allowed on the East side of the road or in the snowplow turnaround.  If you can't park in the signed area, park further down the road in a place where you are not obstructing traffic.

recent observations

We toured the upper ridges south of Granite Mt proper yesterday and found plenty of soft snow and a strengthening snowpack.  Visibility has been the biggest hazard for the last few days with fog and clouds reducing visibility above 7200 feet to almost nothing.  We dug a pit on a SW facing slope at 7400 feet and found just under 4 feet of dense and well consolidated snow. Pit tests revealed no instabilities in this area. Thursday's freezing mist crust was visible under about 3 inches of new snow but was not noticeable on skis. 

A northerly pit on the opposite side of the  same ridge closer to 7600 showed some instabilities in the upper portion of the snowpack mostly focused on storm/old snow interfaces.  We were able to produce failures in Compression Tests that failed on a layer of grauple but did not fail in an Extended Column Test(no propagation).  We also isolated another weak layer 2 feet down that failed on a layer of rounding near surface facets but also lacked propagation potential.  Two additional old snow surface layers held some preserved surface hoar but did not react to our tests.  The snowpack in this area was just over 6 feet deep.

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 23 deg. F.
Max. temperature in the last 24 hours: 27 deg. F.
Average wind direction during the last 24 hours: NW
Average wind speed during the last 24 hours: 3 mph
Maximum wind gust in the last 24 hours: 13 mph
New snowfall in the last 24 hours: 2 inches
Total snow depth: NA inches

.SHORT TERM...Today through Tuesday...Areas of fog currently in
the valleys should dissipate by noon. Moist westerly flow
aloft will continue to bring Pacific storms into our area with
two main ones during the short late tonight through
Sunday, and the other Monday night and Tuesday. The first storm
will come with high snow levels and little impact on road travel
due to snow, but Tuesday`s storm will lower the snow level
enough for several inches accumulation in the west-central Idaho
Mountains. No watches or advisories will be issued on this just
yet, though. Returning to the first storm, pockets of cold air
will be slow to mix out tonight in the valleys of northern Malheur
County and the Owyhee Mountains so we have added a slight chance
of freezing rain early Sunday morning until eventual mixing
changes it to plain rain. This storm will bring widespread pcpn
with generally .20 to .30 inch of liquid equivalent, greatest in
the Boise Mountains and west-central Idaho Mountains. Tuesday`s
storm will bring only slightly less. Snow levels during the first
storm will range from 5300 feet north to 7000 feet south so most
areas will have rain. Tuesday`s storm will be a little colder
with snow levels 4000 feet north to 5000 feet south. Winds do
not look to be a factor in either storm.

.LONG TERM...Tuesday night through Saturday...A short wave trough
begins the period bringing widespread showers to the area. Snow
levels begin around 3500 feet MSL before climbing to near 7000 feet
MSL by the end of the period. An upper level ridge begins to amplify
offshore pushing the storm track north of our area. This will dry
things out for much of the area leaving our northern counties from
Baker down into Washington and over to Adams and Valley with
lingering showers. Temperatures remain above normal.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: A 50 percent chance of snow. Areas of fog before noon. Otherwise, cloudy, with a high near 34. South wind 3 to 6 mph. Total daytime snow accumulation of less than a half inch possible Rain and snow likely, mainly after midnight. Areas of fog before midnight. Snow level 5000 feet. Otherwise, cloudy, with a low around 30. Light southeast wind. Chance of precipitation is 60%. New snow accumulation of less than a half inch possible. Rain and snow. Snow level 5300 feet. High near 36. South southeast wind 5 to 7 mph becoming southwest in the afternoon. Chance of precipitation is 100%. New snow accumulation of less than a half inch possible.
Temperatures: 34 deg. F. 30 deg. F. 36 deg. F.
Wind direction: S SE S
Wind speed: 3-6 Light 5-7
Expected snowfall: Trace in. Trace in. Trace in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: Snow likely. Cloudy, with a high near 26. South wind 13 to 17 mph. Chance of precipitation is 60%. Total daytime snow accumulation of 1 to 3 inches possible. Snow likely, mainly after midnight. Cloudy, with a low around 23. South wind 11 to 16 mph. Chance of precipitation is 70%. New snow accumulation of 1 to 3 inches possible. Snow. High near 28. South wind 9 to 18 mph. Chance of precipitation is 100%. New snow accumulation of 4 to 8 inches possible.
Temperatures: 26 deg. F. 23 deg. F. 28 deg. F.
Wind direction: S S S
Wind speed: 13-17 11-16 9-18
Expected snowfall: 1-3 in. 1-3 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.