THIS AVALANCHE ADVISORY EXPIRED ON February 16, 2019 @ 5:39 am
Avalanche Advisory published on February 15, 2019 @ 5:39 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Tuesdays storm snow is slowly settling and gaining strength but more is on the way over the next two days.  Your best choice right now is to continue choosing conservative terrrain through the weekend. Watch for wind slab development on all aspects at treeline and above in steep terrain near ridgelines and in gullies.

How to read the advisory

Tuesdays storm snow is slowly settling and gaining strength but more is on the way over the next two days.  Your best choice right now is to continue choosing conservative terrrain through the weekend. Watch for wind slab development on all aspects at treeline and above in steep terrain near ridgelines and in gullies.

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.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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On Valentines day the high terrain saw brisk winds out of the east and this weekend they will be switching to south-southwest. There are ample amounts of loose snow available to form sensitive wind slabs in any areas exposed to the wind right now. Steep terrain below ridgelines, cross-loaded gullies and steep terrain (over 35°) should be approached with respect this weekend. Pay attention to changes in snow density and watch for cracking in the snow surface, if you are paying attention this problem should reveal itself.

Avalanche Problem 2: Storm Slab
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Tuesday was big! The Cabinets recieved over two feet of fresh storm snow while the Purcells came in with about 16" plus of settled powder. This new snow has made progress in settling and gaining strength; however, more is on the way. Whether the new snow comes in and forms a slab is still hard to nail down but I would use caution poking into steep terrain this weekend. In areas protected from the wind it is less likely to cause a problem, save the big, steep and open terrain for another day.

Avalanche Problem 3: Persistent Slab
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Still there! Mid-January surface hoar layer is reactive at middle elevations in the Purcell Range, this weak layer has typically announced itself with collapsing and cracking at around 5,500'. In the Cabinets we can still find it but it has not proven to be reactive in stability tests and is unlikely to cause you a problem.  It will be difficult to trigger a slide on this layer; but, If it goes it will go big.



 

advisory discussion

Yesterday we hit up Flatiron to check out the new snow and the old weak layer. On the drive up Pipe creek there was abundant evidence of the recent storm slab problem as many of the steep cutbanks had cracked or released above the road.



Our pit results on Flatiron showed the storm snow to be gaining strength and I was unable to kick anything loose on the steeper convex rolls near ridgeline. The buried weak layer was still quite noisey and produced multiple cracks above 5,500'. This layer will need some steep terrain and room to move to cause you a problem, the kind of terrain you may find in big, steep openings on Rock Candy or Northwest Peaks area. I would be alert to this possibility in those locations as this layer does not seem to be gaining strength quickly and becomes more reactive as we throw the additional snow loads on it. Other observations of note included a stiff and cold breeze out of the east once you gain the ridgelines and evidence of cornice buildup caused by the southwesterly winds during the past storm. Stay safe this weekend and enjoy the new snow!

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
350 AM MST Fri Feb 15 2019

DISCUSSION: A broad, yet well defined area of surface to mid-level
(surface to about 6000 feet above ground level) convergence has 
developed overnight generally along the Idaho/Montana border. This
is all within the area where relatively colder Canadian air
flowing over the Continental Divide is interacting with a steady
stream of warmer, moist air with a stalled warm frontal boundary.
This region has served to rapidly enhance snow showers overnight 
across the Bitterroot, Clearwater and even Mission Mountains and
this will likely continue through much of today. Late this
afternoon a cold front will pass through the region and displace
the convergence area by pushing the Canadian air back east of the
Continental Divide. Although snow showers are likely to persist
overnight they will be not nearly as intense with lesser coverage.
This will also gradually transition the density characteristics of
our new snow from the wetter stuff we're getting right now to a 
much drier powder tonight.

Post-frontal convective showers of light, powdery snow are
expected on Saturday across NW Montana early on, but spreading 
south throughout the day. Saturday night should see an uptick in
snowfall as an arctic cold front glides southeast across the 
Divide and reaching the Montana/Idaho border by Sunday morning. It
seems quite likely that this boundary will stall along the 
Bitterroot Mountains and thus could result in a prolonged period 
of steady light powder in the mountains.

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Sat      
Cloud Cover           90%          90%          90%      
Hi/Lo Temps           22 to 29     19 to 23     21 to 29 
Winds(mph)            S 10G28      SW 14G32     SW 11G30 
Precip Chc            80           50           70       
Precip Type           snow         sno/shr      sno/shr  
Liquid Amt            0.11         0.16         0.20     
Snow Ratio(SLR)       17:1         17:1         18:1     
Snow Amt(in)          1-4          2-4          3-5      
Snow Level            2000         1500         1000     
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.

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