Area Forecast Discussion
Issued by NWS Missoula, MT

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377
FXUS65 KMSO 031102
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
402 AM MST Sat Dec 3 2016

...SIGNIFICANT WINTER STORM FOR NORTHERN ROCKIES SUNDAY/MONDAY...

.DISCUSSION...

Periodic light snow will move across the Northern Rockies through
this morning. Hazardous winter driving conditions, including
slick road surfaces and occasional low visibility, will be present
during this time. Mountain passes will be most susceptible to
variable winter driving conditions. Temperatures will warm above
freezing by late this morning, allowing much of the snow and ice
to melt off of area roadways.

A significant change in temperature and snow will arrive over the
Northern Rockies beginning tonight.

FIRST: A surge of Pacific moisture will become concentrated over
the region tonight, wringing out copious amounts of snow for high
elevations of north central Idaho and western Montana through
Sunday. Upper level winds are anticipated to provide a bit of a
drying, downslope effect to the broad western Montana valleys.
Despite downslope effect, there will be a period of moderate
snowfall across all elevations late Sunday night. Storm total snow
accumulations of greater than a foot are anticipated over area
mountain passes, while valleys will generally have up to 3 inches
accumulation tonight through Monday morning.

SECOND: By Monday morning, arctic air will begin moving westward
across the Continental Divide, allowing temperatures to plummet.
Wind chill in the sub-zero range will be common late Monday night
through Tuesday, particularly in the wind prone areas of Bad Rock
Canyon near Kalispell and Hellgate Canyon near Missoula. All
creatures residing outdoors, such as livestock, domestic pets, and
the traveling public, will be at risk of rapid frostbite or other
cold weather ailments. Exposed skin in these cold, windy
conditions will be injured in a matter of minutes.

THIRD: Cold air will settle into area valleys Tuesday and
Wednesday nights, with air temperatures bottoming out in the sub-
zero range. Again, those outdoors will be at risk for cold weather
ailments.

Beginning Thursday night, Pacific air will resume flowing over
the Northern Rockies, quickly moderating temperatures. The cold
air that will already be in place and Pacific moisture feed may
create an interesting heavy snow scenario through next weekend.
There are some timing issues that need to be sorted out, however
it will definitely will be a wild next week of winter weather.

&&

.AVIATION...Periodic snow will move over area terminals through
03/1800Z, dropping ceilings and visibility at times. KGPI and KMSO
will be most susceptible to snow during this time, with only a
small chance for KBTM and KSMN to be similarly impacted. There
will be a short respite from snow at terminals, however the threat
for low ceilings and visibility will increase after 04/0000Z.
Ceilings and visibility will become deteriorated for hours at a
stretch for KGPI, KMSO, and KBTM, particularly from 04/0300Z
through 04/0900Z. Mountain obscurations will be commonplace during
the next 24 hours as well.

&&

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

     Winter Weather Advisory until 11 AM MST this morning
     Butte/Blackfoot Region.

     Winter Weather Advisory until 11 AM MST this morning
     Potomac/Seeley Lake Region

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

     Winter Storm Watch from late tonight through Monday morning
     Bitterroot/Sapphire Mountains.

     Winter Weather Advisory until 11 AM MST this morning
     Flathead/Mission Valleys...Kootenai/Cabinet Region...Lower
     Clark Fork Region...West Glacier Region.

     Winter Storm Watch from this evening through Monday morning
     Flathead/Mission Valleys...Kootenai/Cabinet Region...Lower
     Clark Fork Region...Potomac/Seeley Lake Region...West
     Glacier Region.

ID...Winter Storm Watch from Sunday morning through Monday morning
     Eastern Lemhi County...Western Lemhi County.

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

     Winter Storm Watch from late tonight through Monday morning
     Northern Clearwater Mountains...Southern Clearwater
     Mountains.

&&

$$



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