Avalanche Advisory published on January 21, 2018 @ 6:17 am
Issued by George Halcom - Payette Avalanche Center
bottom line

The avalanche hazard is Moderate above 6000 feet today.  Up to 18 inches of light new snow has potential to sluff on slopes over 38 degrees. The combination of gusty winds from multiple points on the compass and over a foot of new snow have created new wind slabs on exposed terrain.  Below 6,000 feet the avalanche hazard is LOW.

How to read the advisory

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

There is about 18 inches of new snow resting on a crust, and for the most part well bonded. The snow has a tenancy to want sluff, or to run with you on steep slopes above 38 degrees. Many steep slopes, especially South, have already slufffed naturally. Use caution, and good sluff management while riding or skiing in exposed terrain where you may get knocked off course, and into the many obstacles that have yet to be buried like rocks and trees. 

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

The storm on Thursday brought with it gusty winds that started from the Southeast and wrapped around the compass to the West during the day.  Wind speeds at Granite Mt were recorded near 30 mph.  The combination of a significant snowfall and wind will have created wind slabs on exposed upper elevation terrain.  These slabs are  going to likely be just below the ridgelines, but may form well down into the midslope....Pay attention to changes in the texture or look of the snow pack in areas that saw the direct effects of the winds and expect newly formed wind slabs on a variety of slopes today.   Cracking, or sudden changes in how deep you are traveling in the snow pack are indicators of wind slabs.   

More snow and significant winds are forecasted Sunday night, which will increase the wind slab avalanche problem for Monday.

recent observations

Saturday 1/20/2018:

We toured up to Hum Lake Saddle in the Lick creek drainage on Saturday, and did not see much natural activity other than sluffing, and minor wind slabs that had failed in the new snow during the storm. Cornices are growing, we observed a Glide crack below the rocks on  a NE face above Hum lake. Our test pits (SW and NW) showed moderate failures in compression on the new snow interface, and no propagation in Extended column tests. The lower snowpack is still damp, and will hopefully freeze solid sooner than later? Coverage has improved greatly, but there still are many trees and rocks that need to be buried. We also noticed a sun crust that formed during the day on steep south slopes.



Friday 1/19/2018:



Thursdays storm laid down around 18 inches of snow that is resting on a thin crust that formed from the warmup. The upper 9 inches of new snow right now is very light density, the kind that snow lovers smile about. Our test results on the crust were moderate in compression, but lacked energy to propagate during an ECT. The rest of the snowpack seemed damp still, but on the path of freezing.

We observed natural wind slab avalanches on E,NE slopes Friday in the Grassy twins and Hazard Lakes area, and also got a report in the Titus lot from a local snowmobiler of a natural wind slab that had pulled out during the storm about 18 inches deep. Time will likely heal the wind slab problem, but stay alert in wind loaded terrain.




Area Forecast Discussion
National Weather Service Boise ID
301 AM MST Sun Jan 21 2018

.SHORT TERM...Today through Monday...Upper ridge will shift east
this morning as a storm system approaches from the west. Snow will
spread into southeast Oregon this afternoon and southwest Idaho
tonight. Latest model runs have trended toward higher precip
amounts, but little change in the temperatures and snow levels,
with a rain/snow mix expected in the lower valleys (including the
Lower Treasure Valley). Portions of southeast Oregon and
southwest Idaho (including the Upper Treasure Valley and Western
Magic Valley) look to receive enough snowfall to expand the Winter
Weather Advisory into those areas for tonight through Monday
morning. Snowfall totals of 1 to 2 inches (locally 3 inches) in
the valleys and 4 to locally 10 inches in the mountains are
expected. The snow will wind down by Monday afternoon but
scattered snow showers will continue over the higher elevations.

.LONG TERM...Monday night through Sunday...The active pattern
will continue through the extended period though each system is
warmer than the next. Lingering showers in the northern portions
of the forecast area Tuesday ahead of the next upper level trough.
Models have been showing less precipitation with warm frontal
passage Tuesday favoring Southeast Oregon with the best chance for
precipitation. Snow levels rise quickly from 3K-4k feet MSL on
Tuesday to 4K to 5k Feet MSL by Wednesday night. Thus the valley
will see all rain ahead of the trough passage with mountains
seeing moderate snow. The cold boundary doesn`t pass through our
area until Thursday with snow levels dropping to valley floors
come Thursday afternoon. Much of the precipitation has pushed into
the central Idaho mountains by this time. Upper level ridge
begins to build northward on Friday keeping the warm front passage
with precipitation on Saturday in our northern zones. Warm and
dry conditions Sunday as the upper level ridge continues to build
across the region. Temperatures remain at or above normal through
the period.


.AVIATION...VFR through Sunday morning except for patchy valley
fog. Clouds increasing and lowering from the west Sunday afternoon
with widespread snow developing in eastern Oregon. This will
spread into southwest Idaho Idaho Sunday evening and continuing
Monday morning. Expect mountain obscuration and MVFR/IFR
conditions, with snow levels at the valley floors. Surface winds
light through Sunday morning becoming southerly and increasing to
10-20 kts Sunday afternoon. Winds aloft at 10k ft MSL northwest
15-25 kts becoming west 20-30 kts by 18z Sunday.

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, increasing clouds, with a high near 29. Calm wind becoming south 5 to 8 mph in the afternoon. Snow. Low around 24. South wind around 8 mph. Chance of precipitation is 90%. New snow accumulation of 2 to 4 inches possible. Snow showers likely, mainly before 11am. Cloudy, with a high near 31. West southwest wind 3 to 6 mph. Chance of precipitation is 70%. New snow accumulation of less than one inch possible.
Temperatures: 29 deg. F. 24 deg. F. 31 deg. F.
Wind direction: S S WSW
Wind speed: 5-8 8 3-6
Expected snowfall: 0 in. 2-4 in. Less than one in.
Granite Mountain at 7700 feet.
  Sunday Sunday Night Monday
Weather: A 20 percent chance of snow after 11am. Increasing clouds, with a high near 19. Wind chill values between -1 and 7. South wind 6 to 11 mph increasing to 12 to 17 mph in the afternoon. Snow. Low around 18. Breezy, with a south southwest wind 15 to 20 mph. Chance of precipitation is 100%. New snow accumulation of 3 to 7 inches possible. Snow showers, mainly before 11am. High near 20. West southwest wind 6 to 9 mph. Chance of precipitation is 80%. New snow accumulation of 1 to 2 inches possible.
Temperatures: 19 deg. F. 18 deg. F. 20 deg. F.
Wind direction: S S WSW
Wind speed: 6-17 15-20 6-9
Expected snowfall: 0 in. 3-7 in. 1-2 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.