Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 162214

Area Forecast Discussion
National Weather Service Missoula MT
314 PM MST Sat Dec 16 2017


An active week of weather is expected this upcoming week as a
series of back to back weather systems moves in. The first weather
system will mainly only affect northwest Montana with light snow
expected during the day Sunday. Although the snow will mainly be
light, snow will likely accumulate on area roads and will bring
slick road conditions to northwest Montana on Sunday.

A stronger surge of moisture will begin to move in Sunday night
into Monday and is expected to bring moderate snow to mountain
passes along MT/ID border and Marias pass. As this stronger surge
pushes into the area, snow levels are expected to gradually rise.
By Monday morning a wintry mix is likely and freezing rain will
be possible during the Monday morning commute, especially across
west-central Montana and north-central Idaho. For northwest
Montana, the better chance of freezing rain will be for valleys
south of Flathead Lake and those surrounding the Libby area. The
precipitation type within the Flathead Valley will likely remain
snow, but only modest confidence exists with this part of the
forecast. Nevertheless, the Monday morning commute could be icy,
especially over shaded areas and bridges.

An even stronger surge of moisture is expected on Tuesday, but
will mainly affect northwest Montana where periods of moderate to
heavy snow will be possible Tuesday morning. During the
afternoon, snow levels are expected to rise and most valleys
transition to rain. This being said, valleys near the Canadian
Border could continue to see snow through the afternoon.

Wednesday is likely to have a lot of changeable weather starting
off with mild temperatures and mixed precipitation, but quickly
switch over to snow and wind with the passage of two cold fronts.
Bursts of moderate to heavy snow are possible in the morning as
the Pacific front moves in from the west and again in the
afternoon with the Canadian cold front dropping down from the
northeast. Increased snow intensity, colder temperature, and
gusty winds may cause very slick roadways and reduced visibility
during much of Wednesday. The main upper level trough is forecast
to pass through rather quickly, so most of the snow will end by
late Wednesday.

Long range models show this first wave of cold air settling
across Montana and even into Idaho by Thursday morning. But it
doesn`t appear to end there. While some moderation seems likely on
Friday and perhaps Saturday, GEFS ensemble guidance, the 12z
ECMWF and 12z UKMet all point towards an even colder push of
arctic air into the Northern Rockies over Christmas weekend. It`s
still a bit too early to know how could things could actually get.
But well below normal temperatures seem possible at this point.
The signal is less clear as far as precipitation goes. Typically
these eastward pushes of cold air tend not to be as favorable for
significant precipitation events, especially when cold air is
already in place. But we should have a better perspective on the
details in the coming days, so please stay tuned!


.AVIATION...Gradual clearing is expected this evening which should
lead to some valley fog development at KGPI, KMSO and KSMN.
However increasing clouds overnight should help lift the freezing
fog into a deck of low stratus clouds. Regardless, it does seem as
though impediments to visibility and ceilings are likely at the
above mentioned air fields as well as across parts of the Northern
Rockies where terrain is likely to be frequently obscured. Snow
should return to all air fields after 17/1600 and persist into
Monday, December 18th.


MT...Winter Weather Advisory from 11 AM Sunday to 11 AM MST Monday
     Lower Clark Fork Region.

     Winter Weather Advisory from 11 AM Sunday to 11 AM MST Monday
     Flathead/Mission Valleys.

     Winter Weather Advisory from 11 AM Sunday to 11 AM MST Monday
     Kootenai/Cabinet Region.


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