Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 071057
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
357 AM MST Wed Dec 7 2016


...LAKE EFFECT SNOW TODAY SOUTH OF FLATHEAD LAKE...
...COLD TEMPERATURES AT OR BELOW ZERO TONIGHT...
...PERIODS OF MODERATE TO HEAVY SNOW THURSDAY EVENING THROUGH
   MONDAY...

.DISCUSSION...Temperatures didn`t quite reach their potential
lows around 0 thanks to partial cloud cover much of the night.
Nevertheless there is enough wind to produce wind chills at or
below zero in many valley locations with the coldest readings of
10-20 below zero in southwest Montana. Temperatures will struggle
to rise too much today thanks to some persistent cloud cover in
some areas and as the arctic boundary hovers over the region.

LAKE EFFECT SNOW around Flathead Lake TODAY... On the south end
of Flathead Lake, lake effect snow is a concern today. As the
winds decrease this morning, the cold air will remain over the
warm lake and convection will be able to organize setting up a
snow band. Polson is the most likely area to be affected, and the
band may waver back and forth between Big Arm and Finley point.
One to three inches of snow is likely in a narrow band, maybe as
narrow as 2 miles wide south of the lake, but much more is
possible.

Cloud cover will diminish later this afternoon through the
overnight hours. The clearing skies will allow temperatures to
fall at or below zero in the valleys of western Montana. Some of
the typical colder valleys including Polebridge, Seeley/Swan
Valley and Clearwater Junction could face overnight lows of 15-20
degrees below zero. A moderate surface pressure gradient will stay
in place overnight and help to produce some gusty winds out of
Badrock and Hellgate Canyon through Thursday morning.

A relatively warm, moist air mass will begin moving into the
Northern Rockies Thursday afternoon or evening and interact with
cold arctic air entrenched throughout the region. The result will
be a prime environment for snow production across all elevations.
Right now we`re expecting ONE TO TWO FEET of snow throughout the
higher terrain of the Clearwater and Bitterroot Mountains along
the Montana/Idaho border, with locally higher amounts quite
possible. Travelers over Lookout, Lolo and Lost Trail Passes
should be prepared for heavy snow.

But potentially more troublesome than these total amounts will be
the intense snowfall rates of 2+ inches per hour possible at
times early Friday morning through Friday evening. Periods of
extremely low visibility along with quickly accumulating snowfall
will make travel very challenging over mountain passes. The lower
valleys throughout the Lower Clark Fork Region, Clearwater &
Idaho County in Idaho should prepare for 6 to 12 inches of
snowfall through Saturday morning. As such we have issued a Winter
Storm Watch to highlight the potential for significant public
impacts. Additional Watches and Advisories are likely to come for
the rest of Western Montana that may include Missoula and
Kalispell where there is a potential for several inches of snow
Friday through Monday.

Thereafter the pattern remains cold and snowy with convective snow
showers/bands possible Saturday afternoon through Sunday.
Additional snowfall accumulations are likely during this time,
but probably more localized. Sunday evening and Monday models are
showing increasing consistency towards an additional push of
warm, moist air over not just the cold air in place, but
interacting with yet another arctic push into the Northern
Rockies. This next arctic could be even colder and longer lasting
than the present conditions with very heavy snow developing along
the arctic cold front.


&&

.AVIATION...Expect persistent cloud cover with partial mountain
obscurations at times today under a northerly flow across the
entire northern Rockies. The widespreadk gusty northerly winds
winds will diminish a bit later this morning. Cloud cover will
gradually diminish late this afternoon through this evening at all
terminals allowing for colder temperatures to settle into the
region. There is a moderate surface pressure gradient that will
remain in place through the morning hours and continue to bring
some gusty winds out of Badrock and Hellgate Canyons which could
impact KGPI and KMSO with periods of gusty winds to 20-25 mph from
the east.




&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch from Thursday afternoon through Saturday
     morning Bitterroot/Sapphire Mountains...Lower Clark Fork
     Region.

     Wind Chill Advisory until noon MST today Missoula/Bitterroot
     Valleys.

     Winter Weather Advisory until 5 PM MST this afternoon
     Flathead/Mission Valleys.

     Wind Chill Advisory until noon MST today Flathead/Mission
     Valleys.

     Wind Chill Advisory until noon MST today Butte/Blackfoot
     Region...Potomac/Seeley Lake Region...West Glacier Region.

ID...Winter Storm Watch from Thursday afternoon through Saturday
     morning Northern Clearwater Mountains...Southern Clearwater
     Mountains.

&&

$$


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