THIS AVALANCHE ADVISORY EXPIRED ON December 30, 2017 @ 5:41 am
Avalanche Advisory published on December 29, 2017 @ 5:41 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

A winter storm has been dropping steady snow for the last 24 hours and is expected to clobber the mountains of NW Montana Friday night and into Saturday.  Expect the potential for natural and human triggered avalanches to rise throughout the weekend as more snow and wind pour into the area.  Stick to lower angle terrain and ridgelines until this new snow has had time to settle and bond.  Remember rapid changes in weather cause rapid changes in snow stability.

How to read the advisory

A winter storm has been dropping steady snow for the last 24 hours and is expected to clobber the mountains of NW Montana Friday night and into Saturday.  Expect the potential for natural and human triggered avalanches to rise throughout the weekend as more snow and wind pour into the area.  Stick to lower angle terrain and ridgelines until this new snow has had time to settle and bond.  Remember rapid changes in weather cause rapid changes in snow stability.

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 has been falling at a steady rate and is expected to increase Friday night into Saturday.  This new snow is arriving at relatively warm temperatures will cause avalanche hazard to increase in steep terrain throughout the weekend as it forms a slab.  This new snow will be resting on lighter, colder snow and surface hoar.  Give this new snow ample time to settle and bond before venturing into steep terrain.  Expect this problem to worsen throughout the weekend as the weather forecast is calling for increasing snow, warm temps and increasing winds.

Avalanche Problem 2: Persistent Slab
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We have been talking about the "persistant slab"  that is 2-3' thick, which is resting on the weak facet layer across the area for a while now.  This layer has become quite stubborn in stability tests but it is still there and may become more reactive as the new storm snow adds additional weight to the snowpack.  Thinner storm slab avalanches may create enough force to cause a "step down" to this deeper weak layer.

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
340 AM MST Fri Dec 29 2017
DISCUSSION: Warm air has continued to advance across central Idaho
and west central Montana mountains this morning, raising snow
levels and temps, albeit gradually. Some SNOTELs have seen a jump
in temperatures, while others have been more gradual. All in all,
warming is occurring and will continue, while precipitation will 
keep enhancing across these areas through the day today. We still 
anticipate dense, heavy snow to pile up in the terrain, with 
effects of strong winds kicking in later this evening and last 
through the day Saturday. 
For mountains in the Northwest: the arctic front has made its way
through the Flathead valley so far and will keep on truckin',
making its way into the Kootenai and further south into the 
Missions/Swans later in the day. Deep cold air has combined with 
gusty winds (which are expected to increase more through the day) 
to make for rather inhospitable backcountry conditions, if the JFS
Canyon reports are any indication. And while the coveted Pacific 
Dump Truck will keep the moisture coming, snow may lessen for a 
period of time this afternoon before re-enhancing this evening 
into Saturday. THIS will be your period of most intense snowfall 
rates, with higher snow ratios still likely (especially when 
compared to your southern neighbors in WC MT and C ID).
Saturday is expected to see a gradual tapering off of snow overall,
though northwest flow will keep light and continuous snow falling
in the terrain across all of the Northern Rockies through Sunday
morning.
--Allegretto

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Sat      
Cloud Cover           100%         95%          90%      
Hi/Lo Temps           17 to 26     -2 to 14     14 to 25 
Winds(mph)            NE 10G21     E 13G25      W 12G29  
Precip Chc            100          100          100      
Precip Type           snow         snow         snow     
Liquid Amt            0.24         0.70         0.16     
Snow Ratio(SLR)       17:1         18:1         19:1     
Snow Amt(in)          3-6          12-16        2-5      
Snow Level            500          500          1500     
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.