Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 052145
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
245 PM MST Mon Dec 5 2016

...VERY COLD TUESDAY AND WEDNESDAY...
...HEAVY SNOW EVENT THURSDAY INTO FRIDAY...

.DISCUSSION...A very active weather week lies ahead, with several
different impacts in several areas.

Tonight a weak shortwave moves across central Idaho causing some
snow, mainly affecting White Bird Hill, Grangeville, and the Camas
Prairie. During the day Tuesday, the winds will turn northerly
causing up-slope flow and more light snow for Grangeville, the top
of White Bird Hill, the Camas Prairie, and especially Hwy 14 to
Elk City and Dixie, which could see another few inches of snow.

Meanwhile in Montana, a cold high pressure system moves into the
area causing temperatures to plummet with strong winds,
especially in the canyon areas. Several wind chill advisories have
been issued for this. Tuesday during the day will not meet the
traditional criteria for an advisory, but it will still be very
cold and will chills will drop down again Tuesday night. Along the
Continental Divide will have the worst conditions, with lesser
impacts around the more populated Bad Rock and Hellgate canyons.

It is also very unusual to have Flathead Lake still at full pool
this time of year, which creates a vulnerability to freezing spray
along the shore. The areas along the lake of most concern are the
southern and southwestern shores.

Thursday evening into Friday another heavy snow event is setting
up. The focus of this event will be central Idaho and northwest
Montana. Currently, another foot of snow or more is expected in 48
hours for most of the central Idaho mountains. Portions of the
Cabinet, Mission, and Swan Range mountains will also see a foot of
snow. With the cold air in place from the previous cold air mass,
valley snow amounts could be around 4 to 6 inches in 48 hours in
Missoula and the Bitterroot valleys. Farther north in the Mission
Valley and Kalispell 2 to 4 inches are expected, with 3 to 5
inches further west in Libby and Troy.

Beyond Friday models agree well on a cool and snowy pattern, but
there is big disagreement on the strength of the systems to
follow. Overall, a cool and snowy weather pattern will continue
for western Montana into next week. For central Idaho, there is
some potential for a mild warm up into next week bringing the
lower elevations back into a rain scenario instead of snow.

&&

.AVIATION...Snow showers are redeveloping this afternoon so the
terrain is obscured and lowered ceilings and visibilities can be
expected under stronger showers. An arctic front is still expected
to move into western Montana tonight. Easterly type winds will
increase as the front overtakes the region by early Tuesday
morning. KGPI will be the most gusty of TAF sites overnight.
Light snow will also move into the region with a low currently to
the west. North central Idaho has highest chances for snow, but
model cross sections also show enough moisture in western Montana
for light snow and low ceilings that may last through Monday
morning.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Wind Chill Advisory from midnight tonight to noon MST Wednesday
     Butte/Blackfoot Region...Potomac/Seeley Lake Region...West
     Glacier Region.

     Wind Chill Advisory from midnight tonight to noon MST Wednesday
     Missoula/Bitterroot Valleys.

     Wind Chill Advisory from midnight tonight to noon MST Wednesday
     Flathead/Mission Valleys.

ID...None.
&&

$$


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