THIS SNOWPACK SUMMARY EXPIRED ON January 1, 2017 @ 11:30 am
Snowpack Summary published on December 31, 2016 @ 6:30 pm
Issued by Ben Bernall - Kootenai National Forest
Avalanche Character 1: Persistent Slab
Persistent Slab avalanches can be triggered days to weeks after the last storm. They often propagate across and beyond terrain features that would otherwise confine Wind and Storm Slab avalanches. In some cases they can be triggered remotely, from low-angle terrain or adjacent slopes. Give yourself a wide safety buffer to address the uncertainty.

Multiple weaknesses and slabs are buried within the snowpack at this time.  Snowpack  analysis and stability tests conducted revealed that these weaknesses were bonding well and showing a low likelihood of reacting to human triggers at this time. 

Bottom Line: Weaknesses in the snowpack have responded well to multiple days of moderate temperatures and no additional loading since Tuesday night.  There are still weaknesses however and backcountry users should assess each slope individually and approach steep slopes with caution.  Snowmobilers riding in the Purcell Range of the Kootenai may find these layers to be more responsive to human triggering due to the thinner snowpack and resulting weaknesses.

Avalanche Character 2: Wind Slab
Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.

Earlier this week the mountains of the Kootenai National Forest were loaded with an additional foot of snow and high winds.  This created some potentially dangerous conditions near exposed ridgelines and on steep windloaded slopes.  Todays travels revealed that these slabs are decreasing in reactivity as ample time has allowed the new snow to settle and bond.

Bottom Line: This hazard is reducing in sensitivity.  Backcountry skiers and snowmobilers pushing their way into very high exposed terrain will be the most likely to encounter this hazard.  Use caution in exposed, high elevation terrain and look for signs of wind loading before committing to a steep slope.

Snowpack Discussion

Today we traveled into the North Fork Keeler country and toured out to Burnt and Survey Mountain.  Extended column tests failed with moderate force and no propagation.  Failures occured underneath 12" of new snow that fell earlier this week, this failure was on the new snow/old snow interface.  Compression tests revealed a weakness 21" below the surface.  Failure occured on a buried surface hoar layer with moderate force (CTM 18 Quality 2 shear).  This layer was not at all reactive in Extended Column tests but it is worth paying attention to as it may be more reactive on steep slopes with a thinner snowpack.

 

Weather and CURRENT CONDITIONS
weather summary

Backcountry Forecast from NWS Missoula issued:

350 PM MST Sat Dec 31 2016



DISCUSSION: Forecast models continue to indicate the potential for

some light snow to develop late this morning into the afternoon

across mainly northwest Montana. Elsewhere, some breaks in the

clouds are anticipated with temperatures slightly cooler than

Friday.



A big change in the weather pattern will begin late tonight as an

arctic front moves across the Continental Divide from Canada and

collides with an upper level weather system from the northwest.

Widespread snow will develop, with the focus of the best

accumulations expected through central Idaho and along the

Bitterroot Mountain chain. In addition, gusty northeast and east

winds will develop as the arctic airmass moves into the region.

Gusty winds up to 40 mph will be possible through favored canyons,

particularly through northwest Montana. Much colder temperatures

will settle into the region by early next week.






Kootenai:



--------------------------- 5000-7000 FT ----------------------------

                                     Tonight        Sun              Sun Night        Mon     

Cloud Cover                  95%             95%              85%               60%     

Hi/Lo Temps                 7 to 14        11 to 16        -4 to 3            4 to 8  

Winds(mph)                  SW 11G37   NE 24G52       NE 22G39     NE 22G41

Precip Chc                    90               60                   30                  0       

Precip Type                 snow           snow               snow              none    

Liquid Amt                  0.14            0.12                 0.01               0.00    

Snow Ratio(SLR)         20:1            20:1                20:1                0       

Snow Amt(in)              3                 2-5                  0                    0       



Snow Level                 0                 0                     0                    0  

Disclaimer

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 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.