THIS AVALANCHE ADVISORY EXPIRED ON January 12, 2018 @ 6:42 pm
Avalanche Advisory published on January 11, 2018 @ 6:42 pm
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

New snow, strong winds and multiple weak layers have created dangerous avalanche conditions at upper elevations.  Now is an easy time to make smart decisions, stay on low angle terrain and give steep slopes a wide berth. This new snow and wind slab will need time to come together.  Strong caution is advised on all terrain above 5,000'.

How to read the advisory

New snow, strong winds and multiple weak layers have created dangerous avalanche conditions at upper elevations.  Now is an easy time to make smart decisions, stay on low angle terrain and give steep slopes a wide berth. This new snow and wind slab will need time to come together.  Strong caution is advised on all terrain above 5,000'.

4. High

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Above Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

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.
    Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
Avalanche Problem 1: Storm Slab
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New snow is coming in dense and warm, this is forming a slab that is bonding poorly to the old snow interface.  This will create hazardous avalanche conditions going into the weekend.  Stay out of harms way by avoiding steep terrain until this new snow has had the time to bond and settle.   Currently snotel sites are not showing the amounts of snowfall that were predicted to fall in the mountains; however, small slides in the storm snow have potential to step down to deeper weak layers if initiated.

Avalanche Problem 2: Persistent Slab
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We still have a layer of buried surface hoar that is reactive and showing potential to propagate across slopes.  This layer is close to 2' thick.  It is also likely to increase in thickness and sensitivity as the current storm piles snow up in the mountians.  We are finding this layer on all aspects above 5,000'.  This weakness is the main concern right now and should be treated with respect.

Avalanche Problem 3: Wind Slab
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Blowing snow and wind were observed to be forming wind slabs above 5,000' on leeward aspects.  These slabs are most likely to be found just below ridge-lines on northeasterly aspects; but, don't rule out the potential to see them on more southerly aspects (especially in the Yaak) if the cool arctic air pushes out of Canada and into the forecast area.  

recent observations

Observations taken from the Western Cabinets today revealed a smattering of potential avalanche problems going into the weekend that are likely to be exacerbated by more expected snowfall and strong winds out of the southwest.  

Two primary weak layers were observed that warrant attention as we move into the weekend.  The most serious is the buried surface hoar layer that is propagating in extended column tests and will likely be stressed by additional snowfall.  The second layer of concern is the interface between the new and old snow is failing with light force.  It is very likely that a small slide in this new storm snow would step down to the deeper weak layer and create large and destructive avalanches.  There have been multiple deaths and close calls just north of the border as a result of such scenarios. Slides are stepping down to weak layers created back in November and December.  Our snowpack in the Kootenai is harboring some very similiar layers and structural weaknesses that are currently giving Canada problems.  

https://www.avalanche.ca/forecasts/kootenay-boundary 

Weather and CURRENT CONDITIONS
weather summary

Backcountry Forecast from NWS Missoula issued:
210 PM MST Fri Jan 12 2018

DISCUSSION: A colder airmass is filtering into northwest Montana
causing the plume of moisture to be shunted over north central
Idaho into western Montana this morning. Arctic air continues to
flirt with the Glacier Park area today. The shower activity will
diminish during the mid to late morning hours. The upper level
flow will become northwesterly this afternoon and a very subtle
disturbance moving through the flow will kick off another round
of widespread shower activity. This shower activity will last well
into Saturday, which is a bit longer then previously forecasted.
The mountains along the Montana/Idaho border and the Glacier Park
area will receive the bulk of the precipitation with this second
round of precipitation.

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
Tonight Sat Sat Night Sun
Cloud Cover 95% 80% 75% 80%
Hi/Lo Temps 23 to 28 31 to 34 25 to 29 32 to 37
Winds(mph) SW 11G25 SW 10G29 SW 4 SE 3
Precip Chc 70 70 0 0
Precip Type snow snow sno/shr none
Liquid Amt 0.13 0.08 0.00 0.00
Snow Ratio(SLR) 14:1 12:1 10:1 0
Snow Amt(in) 1-3 1 0 0
Snow Level 3000 3000 3500 4000

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.