491
FXUS65 KMSO 041854
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
1254 PM MDT Fri Sep 4 2026

.DISCUSSION...

KEY MESSAGES:

-  Some stronger showers and storms possible Saturday especially
   during the afternoon.

-  Widespread showers increasing Sunday into Monday with
   seasonably cool temperatures persisting into early next week.

-  Gradual drying trend develops mid-week alongside morning
   valley fog.

A broad trough of low pressure over the Pacific Northwest will
maintain unseasonably cool conditions across western Montana and
north-central Idaho, with valley high temperatures remaining 5 to
10 degrees below normal in the 60s and 70s. Showers Saturday
morning east of US Highway 93 and across northwest Montana will
yield to partial afternoon clearing. Solar heating will generate
weak to modest instability, supporting spotty afternoon showers
and thunderstorms capable of brief heavy rainfall, lightning,
hail, and erratic convective outflow gusts of 25 to 45 mph.

An upper-level closed low will track directly across the Northern
Rockies Sunday through Monday before departing Saskatchewan-bound
by Tuesday. Dynamic forcing and rich moisture advection will
produce widespread, soaking rainfall. Probabilities for rainfall
exceeding 0.50 inches are very high between Sunday morning and
Tuesday morning reaching 80 to 90+ percent across West- Central
and Northwest Montana, 60 to 80+ percent across North-Central
Idaho, and as low as 40 percent for Southwest Montana. A 10
percent chance exists for total rainfall exceeding 2.00 inches in
West- Central and Northwest Montana through Tuesday morning. Cold
air entrainment aloft will lower snow levels, producing some
mountain snow accumulations above 9,000 feet.

The forecast becomes a bit uncertain toward the middle part of
next week, but what we know so far is:
The closed low exits to the northeast on Tuesday, allowing high
pressure to build over the region into the middle of next week.
This pattern will bring a drying trend with moderating
temperatures, though lingering boundary-layer moisture will
continue to support overnight and early morning valley fog and
low stratus.

&&

.AVIATION...The low pressure system over the Pacific Northwest
will continue to cause southwesterly flow over the Northern
Rockies for the next 24 hours. Latest radar and satellite is
showing the next disturbance that will impact the area is
currently over southwest Idaho. This feature will track across the
region this evening and overnight causing rain to impact KSMN,
KBTM, KHRF and KMSO. The rain could be heavy enough to cause MVFR
conditions for a period time at these terminals. The shower
activity across northwest Montana appears to be less extensive so
impacts to KGPI will be lower than the other terminals.


&&

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

$$