Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 160406
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
906 PM MST Fri Dec 15 2017

.UPDATE...Added the lower valleys of the Camas Prairie, including
Orofino and Kooskia to the Winter Weather Advisory.


&&

.DISCUSSION...Accumulating snow has occurred in the lower valleys
of Clearwater County, including Orofino, and is likely to
continue through the night. Slick roads can be expected for those
traveling overnight tonight and in the morning.

Precipitation has been slow to make it into many areas of
southwestern Montana and the southern Bitterroot Valley this
evening. However accumulating snow of 1 to 2 inches, with
isolated areas seeing up to 4 inches in the hills above the
valley, is still expected by morning.


&&

.AVIATION...A cold front is going to be impacting the Northern
Rockies for the next 12 to 18 hours. KGPI is already experiencing
light to moderate snowfall and this should linger until at least
16/01z. Snow will move into KMSO around 15/23z, KBTM around 16/03z
and finally KSMN around 16/05z. After the passage of the front,
widespread snow showers will be lingering throughout the Northern
Rockies. These showers will be diminish from the northern to
southern ends of the forecast area late tonight through Saturday.




&&

.PREV DISCUSSION... /ISSUED 242 PM MST Fri Dec 15 2017/

DISCUSSION...A cold front is moving into north central Idaho and
north west Montana this afternoon. This front is the focal point
for moderate snowfall which is creating snow covered roads. This
front will be steadily moving southward the rest of the afternoon
and evening. The snow could be over the I-90 corridor from
Alberton to Bearmouth during the evening rush hour. Another
concern is that parts of southwest Montana has warmed into the mid
40s today. So snowfall could melt on the road ways and refreeze
creating icy conditions, especially along the I-90 from Warm
Springs to Butte and also HWY 1 from Philipsburg to Anaconda.

The front will push out of the region by Saturday morning, but
widespread snow showers will be lingering throughout the morning.
The showers steadily diminish during the afternoon and evening.
Valley inversions should be wiped out by Saturday allowing
temperatures to warm to near seasonal readings.

Starting Sunday, another weather system will start to move into
Northwest Montana. Light snow is expected to begin in the morning
and should slightly increase in intensity during the afternoon.
Overall, most of the snow during the day Sunday will be across
northwest Montana where about an inch of snow is expected with
localized amounts of up to 2 inches.

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. For valleys, the
forecast is a bit more tricky with snow levels rising early Monday
morning. If valley inversions hold through Monday morning, we
could potentially see some light freezing rain Monday morning
mainly across west-central and parts of northwest Montana. Some
models are slower in the warmer air arriving Monday and if those
models hold true, snow showers are likely on Monday morning.
Whichever scenario is realized, Monday morning commute will likely
get impacted and travel will be slower than normal.

The feed of moisture that arrives on Monday will continue through
Tuesday in the Clearwaters of north-central Idaho and in
northwest Montana, so there may be little if any break in
precipitation in these locations before the next weather system
arrives.

There has been little change to the middle of the week weather
system. The trough and cold front are still on track to pass
through north-central Idaho and western Montana during Wednesday.
Snow levels should rise early Wednesday so precipitation may
start out as a mix of rain and snow in the valleys before changing
to all snow with the cold front. A weak easterly arctic push is
also possible for later in the day on Wednesday so gusty winds and
increased snow intensities are also possible. Widespread travel
impacts are likely with the trough and cold front due to slick
roadways and low visibility.

Northwesterly flow looks to develop on Thursday and remain into
the weekend. This flow pattern appears to be relatively cold and
fairly dry, but weak disturbances have the potential to bring
light snow.

AVIATION...A cold front is going to be impacting the Northern
Rockies for the next 12 to 18 hours. KGPI is already experiencing
light to moderate snowfall and this should linger until at least
16/01z. Snow will move into KMSO around 15/23z, KBTM around 16/03z
and finally KSMN around 16/05z. After the passage of the front,
widespread snow showers will be lingering throughout the Northern
Rockies. These showers will be diminish from the northern to
southern ends of the forecast area late tonight through Saturday.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory until 11 AM MST Saturday Butte/Blackfoot
     Region.

     Winter Weather Advisory until 11 AM MST Saturday
     Bitterroot/Sapphire Mountains.

     Winter Weather Advisory until 11 AM MST Saturday
     Missoula/Bitterroot Valleys...Potomac/Seeley Lake Region.

     Winter Weather Advisory until 11 AM MST Saturday
     Flathead/Mission Valleys...Lower Clark Fork Region...West
     Glacier Region.

     Winter Weather Advisory until 11 AM MST Saturday
     Kootenai/Cabinet Region.

ID...Winter Weather Advisory until 11 AM MST Saturday Eastern Lemhi
     County...Western Lemhi County.

     Winter Weather Advisory until 10 AM PST Saturday Northern
     Clearwater Mountains...Southern Clearwater Mountains.

     Winter Weather Advisory until 10 AM PST Saturday
     Orofino/Grangeville Region.

     Winter Weather Advisory until 10 AM PST Saturday ABOVE 2000 FEET
     for the Lower Hells Canyon/Salmon River Region.

&&

$$



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