THIS AVALANCHE ADVISORY EXPIRED ON January 10, 2018 @ 5:13 am
Avalanche Advisory published on January 9, 2018 @ 5:13 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Heavy mountian snows and high winds are forecast for the coming week.  This will further bury a layer of weak surface hoar and create touchy slab conditions.  Expect this slab to thicken and become more dangerous as the week progresses!

How to read the advisory

Heavy mountian snows and high winds are forecast for the coming week.  This will further bury a layer of weak surface hoar and create touchy slab conditions.  Expect this slab to thicken and become more dangerous as the week progresses!

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: Storm Slab
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Snowfall from last weekends' system has resulted in a thin and reactive slab on all aspects above 5,000'.  This thin slab varies in thickness (4-10") depending on location, it is sliding on a layer of buried surface hoar that can be found on most aspects above 5,000'.  This layer will become thicker and more reactive as heavy mountian snowfall and high winds blanket the region.  Stay safe by avoiding steep slopes over 30° until this new storm snow has had ample time to settle.

Avalanche Problem 2: Wind Slab
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Yesterday we observed extensive evidence of wind loading on north and easterly aspects were southwest winds have created thicker slab conditions overlying the previously mentioned weak layer.  Weather forecasts are calling for an increase in this southwest wind component and incoming snowfall, which will exacerbate this problem.  Avoid steep terrain on leeward slopes and look for a "pillowy" texture in the snow or changes in density of the surface snowpack.

Avalanche Problem 3: Loose Wet
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With warm temperatures and an expected snowline near 5,000' it is likely that we will see some classic warm weather activity such as rollers, and loose snow point releases.  These conditions may cause a concern if one is entrained in a small slide where trees or gullies may cause an increase in consequences.  This problem should decrease as the week progresses and snowlines drop to the valley floors.

recent observations

On January 8th Nate and I travelled into the Keeler Rattle area.  We found a smattering of potential problems with the most notable being the buried surface hoar that was preserved and buried under last weekends storm.  This surface hoar is buried about 1" below a thin rain crust. On wind loaded aspects it was 10-12" deep and about 4" deep on the windward side.  It released with light force and showed the potential to propagate on leeward aspects where there is a thicker and more cohesive layer above it.  I was also able to get it to break and release on small, test slopes (see photo).



Slab released at 6,100' on east aspect. 10-12" thick.

Other observations of note where some wind loading directly below ridgelines on easterly aspects and some small "loose-wet" point releases on sunny aspects.

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
400 AM MST Tue Jan 9 2018

DISCUSSION: An active pattern for the next few days, starts 
today. Heavy mountain snow and gusty winds will move into the 
Northern Rockies this afternoon, and will likely persist until the
weekend, with a brief break Thursday morning. Snow levels will
start off above 5000 feet this afternoon, then lowering to 2000 
feet by tomorrow morning. So, initially some lower mountain 
ranges could see a mix of rain and snow, with a heavy wet snow in 
the higher mountain ranges. A more significant system is still on
track for Thursday into Friday. Substantial amount of snow is
anticipated for the higher terrain with this system. 

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Wed      
Cloud Cover           95%          90%          95%      
Hi/Lo Temps           31 to 34     18 to 22     23 to 27 
Winds(mph)            SW 17G41     SW 16G32     SW 10G21 
Precip Chc            100          80           70       
Precip Type           snow         snow         snow     
Liquid Amt            0.43         0.14         0.08     
Snow Ratio(SLR)       11:1         14:1         17:1     
Snow Amt(in)          4-7          1-4          1-2      
Snow Level            4500         2500         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.