Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 172200

Area Forecast Discussion
National Weather Service Missoula MT
300 PM MST Fri Nov 17 2017


Snow shower activity will slowly weaken over the Northern Rockies
this evening through Saturday. A quick inch of snow is possible
over the mountain passes through Saturday morning, particularly
Lolo and Lookout Passes. Valley locations will see only up to a
trace snow accumulation tonight. By Saturday afternoon, much of
the snow activity will be confined to the higher terrain, with
little to no accumulation anticipated.

Conditions dry and skies clear somewhat across the Northern
Rockies Saturday evening through Sunday midday. The decrease in
cloudiness and valley winds will allow temperatures to drop
rapidly to the single digits across southwest Montana valleys and
Lemhi County Idaho. Elsewhere, cloudiness and a mix of low stratus
and patchy freezing fog will develop and likely keep
temperatures warmer than single digits. Impacts of freezing fog
will be to reduce visibility for those traveling through the area.

Sunday afternoon through Monday afternoon another weak storm
system will move across the Northern Rockies, bringing snow
primarily to high terrain and passes along Montana-Idaho border
(Bitterroot/Clearwater Mountains). There is high certainty that
snow on roadways will slow travel over area mountain passes,
particularly Lookout, Lolo, and Lost Trail Passes (4 to 8 inches
new snowfall expected). Other area passes will also experience
snowfall, however mostly in the sub 3 inch range. The northwest
flow at the ridgetops may allow some of the snow to impact the
valley roadways for a short while on Monday morning, especially
for locations such as Missoula Valley and Seeley-Swan region.

Relatively warm high pressure is expected to drift over the
Northern Rockies for Wednesday through the weekend, however this
pattern will be more wet than the dryness usually associated with
high pressure. Moisture from the Pacific will be streaming over
the high pressure during much of this time, with the "warm" air
keeping snow levels mostly above 4000 feet for much of this time.
Idaho-Montana border high elevations appear to capture quite a bit
of moisture (mostly snow) during this time, with snow pack
continuing to steadily increase.


.AVIATION...Snow showers will continue into this evening with
brief reductions in visibility and lowered ceilings. Breezy winds
will also continue until sunset then diminish. As the atmosphere
dries, showers will diminish overnight although some shower
activity will continue on the mountains into Saturday morning with
terrain obscurations at times. Patchy fog is possible for Saturday
morning at KMSO and KGPI but considerable cloud cover and the
drying factor of this afternoon`s wind will limit the potential
for widespread fog.




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