112
FXUS65 KMSO 210800
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
200 AM MDT Mon Sep 21 2026

.DISCUSSION...

KEY MESSAGES:

-  Chance for showers/thunderstorms in Lemhi County and southwest
   Montana on Tuesday

-  Warm, dry week ahead for the rest of the region.

-  Showers return late next week or early next weekend.


Satellite imagery early this morning shows dry air under a ridge
of high pressure over the northwestern U.S. including the
Northern Rockies. A closed circulation of low pressure is spinning
over central California and moving inland. The ridge of high
pressure will keep the Northern Rockies dry today, with high
temperatures about 10 degrees above normal. Patchy morning fog
will affect some valleys of western Montana. Fog will remain in
the forecast into midweek. The California low will track northeast
today and on Tuesday. By Tuesday afternoon, moisture associated
with that system will enter Lemhi County and southwest Montana,
including Salmon and Butte, resulting in chances for showers and
possibly thunderstorms in the late afternoon and evening. The
moisture feed is short-lived, though, and dry conditions with
above-normal temperatures will continue through Thursday.

A shift towards more seasonable temperatures and chances for
precipitation arrive on Friday. Most model ensemble members (about
75%) are in favor of a trough of low pressure digging along the
Canadian coast and moving into the Pacific Northwest by Saturday.
Details on this event are still unclear, as there is little
agreement on timing and intensity of this system. Regardless of
precipitation chances, expect a shift back towards seasonable
temperatures on Friday lasting through next weekend.



&&

.AVIATION...Keeping fog in the 21/0600Z TAFs for KGPI, KMSO, and
KSMN this morning. Calm winds, clear skies, and dew point
depressions almost identical to yesterday (Sunday) point towards a
repeat of fog forcing IFR conditions for this morning, especially
at KGPI. Beyond morning fog, high pressure will bring fair
weather across the Northern Rockies airspace. Expect light and
variable winds under mostly sunny skies today.



&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

$$