Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 292105

Area Forecast Discussion
National Weather Service Missoula MT
305 PM MDT Thu Oct 29 2020

.DISCUSSION...Sunny skies, except for some morning fog in the
lower valleys, prevail across the Northern Rockies today.
Temperatures warmed up quite nicely: into the 50s and even lower
60s in some spots. There were a couple of exceptions where the
inversion did not lift, namely Missoula, where temperatures
have struggled to reach 40 degrees. Expect one more night of high
pressure, valley inversions, and resultant valley fog.

A weather disturbance will move through the Northern Rockies
Friday afternoon through Saturday morning. As it does so, expect
breezy conditions to develop with wind gusts to 25 mph, with some
locally higher gusts to 35 mph. A Lake Wind Advisory has been
issued for Flathead Lake, as these breezy conditions will bring
choppy conditions to the lake through the evening.

The other impact from this system will be showers developing along
the frontal passage. These showers will move from northwest
Montana through southwest Montana between early afternoon and
early evening. Showers should remain as rain in valleys overall,
however any remaining cold pockets could see a mix of snow
(confidence is low).

Saturday afternoon, a ridge of high pressure will quickly
redevelop and persist through Tuesday. Expect dry weather with at
or above seasonal temperatures. The stable air under the ridge may
lead to increasing stagnant air and the potential for valley fog
once again. A transition to a moist westerly flow aloft is
expected around the middle of next week, which would result in an
increase in moisture, especially in the mountains.

Late next week, models remain consistent showing a low pressure
trough amplifying over the western US. This would open the door
for colder air and a potential for valley and mountain snow to
make a return.


.AVIATION... Strong valley inversions will persist through
30/1800z. Expect a redevelopment of fog after 30/0900z at KGPI and
KMSO persisting through 30/1600z. KSMN and KBTM can expect VFR
conditions through 30/1800z. A strong cold front will move through
the Northern Rockies Friday afternoon. The biggest impact from
this front will be westerly winds gusting 15-25 mph through
31/0200z. Showers are also possible along the frontal passage
which may temporarily lower visibility and ceilings.


MT...Air Stagnation Advisory until noon MDT Friday
     Bitterroot/Sapphire Mountains...Flathead/Mission Valleys...
     Kootenai/Cabinet Region...Lower Clark Fork Region...
     Missoula/Bitterroot Valleys...Potomac/Seeley Lake Region...
     West Glacier Region.

     Lake Wind Advisory from noon to 8 PM MDT Friday Flathead/Mission

ID...Air Stagnation Advisory until 11 AM PDT Friday Lower Hells
     Canyon/Salmon River Region...Northern Clearwater
     Mountains...Orofino/Grangeville Region...Southern
     Clearwater Mountains.


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