Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 040352
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
852 PM MST Sat Dec 3 2016

.UPDATE...The winter storm watch for northwest Montana has been
converted to a winter weather advisory for the upcoming storm.

&&

.DISCUSSION...A complicated weather system will be impacting the
region and the details are still not certain. The first Pacific
front will bring in widespread precipitation to northwest Montana
later tonight through Sunday morning. This first push will bring
some decent snow accumulations above 2500 feet, so impacts will be
minimal in Libby, Troy and Eureka. While Hwy 2 around Happy`s Inn
and Hwy 93 in Olney will have moderate impacts. Then the
precipitation will diminish during the afternoon. A second polar
front from the northeast will intensify the snow Sunday night. The
models are still struggling on the placement of the heaviest snow
with this second front. The consensus of the models indicate that
the best snow will be along Hwy 93 from Eureka through Kalispell
and eastward toward Glacier Park. This second push might have a
bigger impact than the first front since gusty easterly winds will
be combining with the accumulating snow to create blowing snow.
Also temperatures will begin to drop rather quickly potentially
creating freeze up on area roads. And the third and final
component to the storm will be the arctic cold front on Monday
night into Tuesday which will cause temperatures to plummet and
create dangerous wind chill readings.

&&

.AVIATION...Banded snow showers in north central Idaho and western
Montana will continue to weaken and dissipate this evening,
though cloud cover and obscured terrain will remain. Snow will
again return for north central Idaho and northwest Montana
overnight and the rest of western Montana during Sunday. We have
issued a mix of winter weather advisories/watches/warnings with
impacts from snow, wind, and dropping temperatures extending into
Sunday night. The higher terrain is expected to receive over one
foot of snow with blowing snow by Sunday evening. Valleys are
forecast to have many inches of snow. A strong cold front will
also pass through the day and evening so increased winds, quickly
dropping temperatures, moderate to heavy snow, and freeze up of
surfaces are also possible with its passage.


&&

.PREV DISCUSSION... /ISSUED 243 PM MST Sat Dec 3 2016/

DISCUSSION...

SNOW, WIND AND TRANSITION TO COLD:
There have only been few changes to the forecast with the
upcoming winter storm. Mountains and passes remain in the path of
moist pacific air that has the right temperature profile to
produce moderate to heavy snowfall tonight through Sunday.
Increased wind will also bring increased concern for very low
visibility in blowing snow Sunday and Sunday evening. Valley
locations are also anticipated to accumulate snow during Sunday
and Sunday night, which will likely accumulate to the biggest snow
event of the season so far. Our main concern, though, is with the
passage of the cold front. The wind, enhanced snowfall, and
colder temperatures could all come together to produce very low
visibility and snow-packed/icy roadways. This cold front will
mainly impact north central Idaho and western Montana during the
afternoon and/or evening.

ARCTIC FRONT:
The northern Flathead Valley through Marias Pass may
start to see arctic air move in from the east as early as Sunday
night, so additional snowfall and gusty east winds may be
observed Sunday night. The arctic front is not expected to move
through western Montana and north central Idaho until Monday
night, so high temperatures on Monday do not look quite as cold
though still below average.

Starting Tuesday morning, we will begin to see Arctic air spill
over the Continental Divide and will lead to dangerous wind chills
of -10F to -25F across western Montana. For central Idaho, a
weather disturbance is expected to bring steady light to moderate
snow on Tuesday and should cause snow to accumulate down to valley
floors. Areas surrounding Whitebird Grade and across the
Clearwater mountains should expect slick travel on Tuesday. Some
light snow showers will also be possible across parts of western
Montana and roads should continue to be slick.

A brief break in precipitation is expected on Wednesday, but cold
temperatures will continue to persist. On Thursday, models have
been consistently showing a warm front moving through central
Idaho and western Montana. With the cold Arctic air in place,
this weather system has the potential for significant valley
snowfall. Stay tuned for more updates next week.

AVIATION...Banded snow showers in north central Idaho and western
Montana will continue to weaken and dissipate this afternoon,
though cloud cover and obscured terrain will remain. Snow will
again return for north central Idaho and northwest Montana this
evening and the rest of western Montana during Sunday. We have
issued a mix of winter weather advisories/watches/warnings with
impacts from snow, wind, and dropping temperatures extending into
Sunday night. The high terrain and passes are expected to receive
over one foot of snow with blowing snow by Sunday evening. Valleys
are forecast to have many inches of snow. A strong cold front
will also pass through the day and evening so increased winds,
quickly dropping temperatures, moderate to heavy snow, and freeze
up of surfaces are also possible with its passage.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch from Sunday morning through Monday morning
     Butte/Blackfoot Region...Missoula/Bitterroot Valleys.

     Winter Storm Warning from midnight tonight to 11 AM MST Monday
     Bitterroot/Sapphire Mountains.

     Winter Storm Warning from midnight tonight to 11 AM MST Monday
     Lower Clark Fork Region.

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

     Winter Storm Warning from midnight tonight to 11 AM MST Monday
     West Glacier Region.

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

     Winter Storm Warning from 11 AM Sunday to 11 AM MST Monday
     Potomac/Seeley Lake Region.

ID...Winter Storm Warning from 8 AM Sunday to 11 AM MST Monday
     Eastern Lemhi County...Western Lemhi County.

     Winter Weather Advisory from 11 PM this evening to 10 AM PST
     Monday ABOVE 3000 FEET for the Lower Hells Canyon/Salmon
     River Region...Orofino/Grangeville Region.

     Winter Storm Warning from 11 PM this evening to 10 AM PST Monday
     Northern Clearwater Mountains...Southern Clearwater
     Mountains.

&&

$$


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