Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 182219

Area Forecast Discussion
National Weather Service Missoula MT
319 PM MST Sat Nov 18 2017


Cloud decks will increase through Sunday, with a relatively warm
airmass over the Northern Rockies. There is a slight chance of
patchy freezing fog tonight through Sunday morning, particularly
for valleys of northwest Montana.

A northwesterly oriented storm system will move over the Northern
Rockies Sunday afternoon through Monday afternoon. A moisture feed
with subtropical Pacific origins will interact with this storm
system to bring snow down below pass elevations briefly late
Sunday night through Monday morning. The greatest chance of snow
accumulation on valley roadways will be found across northwest
Montana on Monday morning, with possible freezing rain in the mix
as well. Be prepared for patches of hazardous winter driving
conditions. Outside of the overnight/early morning hours, snow
accumulations will be concentrated over Lookout, Lolo, Lost Trail,
and Marias Passes. Lookout Pass is anticipated to receive 6 to 9
inches accumulation over the storm, whereas other passes mentioned
will have accumulations closer to the 4 to 6 inches range.
Hazardous winter driving conditions will linger for the passes
through early Monday afternoon. Snow levels will rise above most
area mountain passes by Monday night, with snow turning to rain
and temperatures slowly warming across the region.

Little has changed with the unsettled pattern next week, with
unseasonable warm temperatures. Mountain snow and valley rain will
begin Tuesday morning, where mountain passes above 5000 feet
could see light snow accumulations of a couple inches. By mid
week, warmer air will move in with another surge of subtropical
moisture, which will push snow levels up to the highest peaks
around the Northern Rockies. Many valleys of north-central Idaho
and western Montana should see moderate rain intensities for a
period of time. Thanksgiving Day still looks like the warmest day
of the week with valleys of western Montana and north-central
Idaho seeing highs in the upper 40s to low 50s, along with
continued rain showers.

A cold front will push through the region late Thursday night,
that will allow snow levels to lower to around 3000 feet. Valleys
around this elevation could see light snow showers during the day
Friday, if enough moisture lingers behind the front.


.AVIATION...Ceilings will increase across the Northern Rockies
during the next 24 hours. High-elevation shower activity across
northwest Montana along Continental Divide will continue during
this time, maintaining low clouds that will obscure much of the
terrain along the Divide. Elsewhere, breezes will be present
through sunset. Patchy freezing fog is possible for some northwest
Montana valleys 19/0600Z through 19/1800Z, however no fog or
freezing fog is anticipated at any major area terminal.



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