THIS AVALANCHE ADVISORY EXPIRED ON February 21, 2018 @ 5:09 am
Avalanche Advisory published on February 20, 2018 @ 5:09 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Sensitive storm snow and wind slabs are resting on a layer of weak facets and a slick bed surface.  Steep terrain (over 30°) should be avoided on all aspects and elevations until this new snow has had time to settle and strengthen.

How to read the advisory

Sensitive storm snow and wind slabs are resting on a layer of weak facets and a slick bed surface.  Steep terrain (over 30°) should be avoided on all aspects and elevations until this new snow has had time to settle and strengthen.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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On Sunday a strong cold front pushed out the weekend storm and brought with it a strong north and easterly wind component. These winds combined with plenty of loose available snow have created very sensitive wind slabs and loading on aspects that are typically on the windward side of the mountains.  These windslabs are likely to be resting on smooth and scoured surfaces as a result of this atypical loading.  

Avalanche Problem 2: Storm Slab
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Snotel sites across the Kootenai picked up an average of 16" of new snow between Friday and Sunday. This storm snow is resting on a weak layer of facets with a thick rain crust lying underneath. This is creating very sensitive avalanche conditions on all aspects and elevations above 4,000'. In sheltered areas (dense timber) this snow is light, loose and not likely to pose a concern.  In areas where it is more open and exposed to the wind it is dense enough to form a slab, expect this storm snow to be easily triggered in open terrain. 

advisory discussion

I would like to remind the backcountry users that a considerable rating suggests that human triggered avalanches are "likely" by definition and a majority of avalanche related deaths occur under a Considerable Rating.  Quite often in these conditions riders will observe someone get away with riding on a steep slope and be lulled into a false sense of security and the notion that it must be safe as a result.  Don't fall into that trap right now, the snow is still very sensitive and will likely stay that way moving forward into the week. Play a conservative game and save the steep terrain for a better day!

recent observations

Observations taken from the East Cabinets verified much of the classic "Bullseye Data" that one looks for when venturing into avalanche terrain.  From the moment I left the car at 3,500' I began to hear audible whoomphing, observed shooting cracks and failures as I climbed and observed extensive evidence of the northeast winds that rolled in with the coldfront.  Multiple hand shears and two test pits confirmed the existence of a layer of weak facets resting on the stout February 4th rain crust.  At 6,000' we have approximately 20" of fresh snow resting on this weak layer that is failing with moderate force and producing a quick, clean shear.  This weak layer will take time to bond. The current cold temperatures will likely slow the bonding process.



Pit showing storm slab (20" thick) failure on facets. ECTP12. 6,000' on NE aspect.

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
440 AM MST Tue Feb 20 2018

DISCUSSION:  
A slowly modifying arctic airmass will remain over the Northern
Rockies for the next several days as temperatures remain 15 to 20
degrees below normal. A trough of low pressure digs into the
Pacific Northwest this afternoon. The bulk of the energy will be
over Washington this afternoon and evening, but enough instability
will be over northwest Montana to create a few snow showers. New
snow accumulations will be light, from a dusting to potentially an
inch. This trough swings through Oregon into central Idaho tonight
into Wednesday. Idaho county into southwest Montana appears to
have the best chance for snow, but moisture continues to be
limited. The higher terrain of Idaho County is only expected to
receive up to 2 inches of new snow. The Northern Rockies remain
under a cold and active weather pattern through the end of the
work week as subtle features push through the region in
northwesterly flow. A more significant system is anticipated for
the weekend. 

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Wed      
Cloud Cover           80%          70%          25%      
Hi/Lo Temps           8 to 16      -5 to 0      11 to 19 
Winds(mph)            SW  5        W  4         SW  4    
Precip Chc            0            0            0        
Precip Type           snow         snow         none     
Liquid Amt            0.00         0.00         0.00     
Snow Ratio(SLR)       22:1         21:1         0        
Snow Amt(in)          0            0            0        
Snow Level            0            0            0        
Disclaimer

Avalanche conditions change for better or worse continually. Backcountry travelers should be prepared to assess current conditions for themselves, plan their routes of travel accordingly, and never travel alone. Backcountry travelers can reduce their exposure to avalanche hazards by utilizing timbered trails and ridge routes and by avoiding open and exposed terrain with slope angles of 30 degrees or more. Backcountry travelers should carry the necessary avalanche rescue equipment such as a shovel, avalanche probe or probe ski poles, a rescue beacon and a well-equipped first aid kit.  For a recorded version of the Avalanche Advisory call (208)765-7323.