Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 030355
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
855 PM MST Fri Dec 2 2016

.DISCUSSION...
Snow has increased across the northern Rockies, with widespread
snow seen across southwest Montana and along the Continental
Divide. MacDonald Pass and Butte/Homestake Pass have already
received an increase in snow accumulations as well as blowing
snow on MacDonald Pass, which has decreased visibility and caused
slick roads in the area. Therefore, the winter weather advisory
has been expanded to include this area through Saturday morning
due to possible travel impacts.

&&

.AVIATION... Snow showers will continue for area terminals KBTM
and KMSO, and be in the vicinity for KGPI, tonight through
Saturday morning. Main impacts will be low ceilings and reduced
visibilities for heavier snow showers. Snow showers are expected
to taper off Saturday afternoon, but a stronger weather system
will be moving in Saturday night.

&&

.PREV DISCUSSION... /ISSUED 309 PM MST Fri Dec 2 2016/

..SIGNIFICANT WINTER STORM WITH MULTIPLE IMPACTS FOR THE
MOUNTAINS AND VALLEYS SUNDAY THROUGH MONDAY...

DISCUSSION...Our first of multiple winter storms will be moving
in this evening and cause periods of light to moderate snow over
mountain passes and valleys across western Montana and central
Idaho. Most valleys will see an inch or less but valleys across
northwest Montana could see up to 2 inches of snow. Mountain
passes such as Lookout, Lolo, Marias and Lost Trail could see up
to 4 inches of snow by mid day Saturday. The snow will likely
cause slick travel conditions for Saturday morning, thus a winter
weather advisory was issued. A stronger weather system continues
on track to impact the region beginning Sunday.

For Sunday...

Mountains and Mountain Passes:

In terms of snowfall amounts, the mountains of the Northern
Rockies will be measured in feet. Along with the snow, we are
expecting strong gusty winds over the mountain passes,
specifically Marias Pass Sunday, through Monday that will produce
very low visibility. People traveling over area passes, such as
Lookout, Lolo, and Marias Pass should expect to encounter
dangerous driving conditions at times, with a total of 1 to 2
feet of snow. Homestake, MacDonald, and Lost Trail Passes will
also see hazardous driving conditions, but not quite as much snow
at 6 to 12 inches.

Valleys:

Most valleys will not see the amount of snow as the mountains,
however this will be the first significant snow storm for the
valleys this season. We are expecting the gusty winds to occur
with the snow here as well. However, most of the strong winds will
be associated with a cold front that will slide south through
western Montana and north-central Idaho, starting in northwest
Montana Sunday morning. The valleys of NW Montana are expected to
see 3 to 6 inches of snow, with isolated higher amounts around
West Glacier, with up to 10 inches. Most of the snow will fall
here from Sunrise Sunday to 5pm Sunday evening, and the strongest
winds from 6am-10am. Portions of north-central Idaho, such as
Weippe to Pierce could see 6 to 11 inches while Whitebird Hill and
Greer Grade could see around 6 inches through Monday morning.

The valleys of western Montana south of I-90, will be shadowed
out for most of the day on Sunday. Most of the snowfall
accumulations here will be along and behind the cold front, with
around 1 to 4 inches. The front is expected to enter the region
around 2pm, with the strongest winds being between 4pm to 8pm.
This will be the most hazardous time to be traveling through the
region, with very low visibility and snow-covered roads.

Due to all these impacts, Winter Weather Watches have been issued
at various times starting early Sunday morning, through Monday
afternoon. Visit www.weather.gov/Missoula to see the start and
finish times for your area.

The coldest arctic air will begin to move southwestward into
northwest Montana Monday night, settling into the rest of western
Montana and central Idaho on Tuesday. Gusty northeast to east
winds are expected to develop, particularly through favored
canyons of western Montana, such as Badrock near Kalispell and
Hellgate near Missoula. The combination of wind and arctic cold,
could make for some dangerous wind chills, especially near the
Continental Divide. In addition, the wind will stir up recent
snowfall, which could cause some blowing snow and poor visibility.
Locations such as Missoula and Kalispell should expect a very cold
Tuesday morning, with possible morning commute impacts due to
lowered visibility. Ahead of the main arctic boundary, portions of
north central Idaho may see light snowfall, which may further
impact area roads through the day Tuesday.

Arctic air will remain settled over the region into Wednesday,
with daytime highs in the low teens and overnight lows in the
single digits to below zero. A moderation of the cold air is
expected to begin Thursday into the weekend. Forecast models
continue to show a potential snow event late in the week, though
timing and details with this system still remain very much up in
the air.

AVIATION...Clouds will be on the increase this afternoon as the
next weather system begins to approach the Northern Rockies. Snow
showers will be on the increase for area terminals KGPI and KMSO
tonight and will continue to linger through Saturday morning. Main
impacts will be low ceilings (especially for KGPI), and reduced
visibilities. Snow showers are expected to taper off Saturday
afternoon, but a stronger weather system will be moving in
Saturday night.

&&

.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 Saturday Butte/Blackfoot
     Region.

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

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

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

     Winter Storm Watch from Saturday 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 Saturday Northern
     Clearwater Mountains...Southern Clearwater Mountains.

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

&&

$$


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