Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 232040

Area Forecast Discussion
National Weather Service Missoula MT
240 PM MDT Mon Oct 23 2017

...Valley fog likely Tuesday and Wednesday, drive with caution...

.DISCUSSION...High pressure will strengthen over the Northern
Rockies tonight and persist through much of Wednesday. As a result
patchy valley fog will develop and be the main impacts to lower
valleys in central Idaho and west central and northwest Montana
both Tuesday and Wednesday morning. Fog may be dense in some areas
including the Missoula Valley.

Late Wednesday into mid day Thursday a pretty strong cold front
will come from the northeast across the continental divide. There
is increasing confidence for the following from this front:

Strong gusty northeast winds. Areas most favorable for these winds
are in the Flathead/Mission valleys and the highway 200 corridor
near Ovando to Missoula.

Accumulating snows on the mountain passes along the continental
divide will bring some difficult travel especially since the snows
will occur mostly at night.

Late Thursday through Sunday pretty strong high pressure for this
time of year will redevelop. The associated stable air will bring
a return to valley fog. Given the time of year and strength of the
ridge this fog could persist through the noontime hours in some
areas. Fog may well end up turning into more of a low stratus in
the Mission Valley by Friday or Saturday. Otherwise expect plenty
of sun and seasonal temperatures.

A pattern change to another arctic system is expected early next



Precipitation features will dissipate across the Northern Rockies
through 23/1800Z, while cloudiness will be slowly eroded by high
pressure throughout the next 24 hours. Patchy fog will be found in
some valleys through 23/1600Z, mainly across northwest Montana.
Terrain obscurations will become less common today, as cloud
decks rise above even the highest mountains along the Continental
Divide tonight. Surface winds will be fairly light, mostly under
10 knots for most area terminals during the next 24 hours. Fog may
become the most significant aviation weather issue 24/0900Z -
24/1800Z for KMSO and KGPI.



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