759
FXUS65 KMSO 052057
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
257 PM MDT Sat Sep 5 2026

.DISCUSSION...

KEY MESSAGES:

-  Some stronger showers and storms possible this afternoon and
   again Sunday afternoon.


-  Significant rain event for much of the Northern Rockies Sunday
   through Tuesday morning.

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

A closed low pressure circulation is visible this afternoon on
satellite imagery along the Washington/Oregon border. This low
will continue to send waves of energy into western Montana and
north central Idaho, increasing shower and thunderstorm activity
through the afternoon. A few isolated strong storms are possible,
mainly across southwest Montana.

A defined area of showers with embedded thunder is anticipated to
develop overnight into early Sunday morning as the low pressure
system slowly wobbles eastwards. Persistent rain is anticipated
generally along the Highway 93 corridor.

As the upper low begins to track into the Northern Rockies Sunday,
upper level forcing in the atmosphere will combine with
significant moisture advecting into the region to bring another
round of showers and a few strong to severe storms. These storms
will be capable of very heavy rainfall rates (0.75 inches per hour
or greater) along with the potential for hail and wind gusts up to
50 mph. The heavy rain in particular could cause localized
flooding issues, particularly if a flood prone area or burn scar
takes a direct hit. Storms will be possible across the entire
region, but the stronger storms are more likely across west-
central and southwest Montana.

By late Sunday night into Monday, widespread moderate to heavy
rainfall will develop across western Montana and north central
Idaho. The probability for half an inch of rain by Tuesday
morning is generally 80 to 100 percent for most locations, other
than the southern end of Lemhi County. The most significant
rainfall is anticipated generally from Missoula county north and
east, including Lake and Flathead counties. Recent model trends
show widespread amounts of 1 to 3 inches of rainfall in these
areas, with up to 3 inches along the Continental Divide,
including over Glacier National Park. There is even a low
probability of 4 inches or more along the higher terrain near the
Divide, including the Mission, Swan and Flathead Ranges. For the
most part, this is expected to be a beneficial rainfall event.
However, locations that receive the higher end totals may see
rapid rises on small streams and creek, rock and debris slides
onto roads, and minor flooding in poor drainage areas.

Some model trends indicate that the low may be slower to exit the
region, possibly lingering rainfall into Tuesday. It does look
like a general drying trend will follow later Tuesday into mid
week though a generally northwest flow aloft may allow for
continued periods of afternoon showers. Warming will also occur,
but it will likely only be to near normal for this time of year.
Lingering boundary-layer moisture will continue to support
overnight and early morning valley fog and low stratus.

&&

.AVIATION...Scattered showers and thunderstorms are possible
across western Montana this afternoon and evening and could
impact KMSO and KHRF. Main threats will be brief heavy rain, wind
gusts to 30 kts and possibly some small hail. Expect generally
weak winds at the terminals. Persistent light to moderate rain
showers are expected to develop overnight through Sunday morning
impacting KGPI, KMSO KHRF and possibly KBTM. Widespread
obscurations of the terrain are anticipated due to lowered
ceilings. More scattered showers and thunderstorms are possible
on Sunday afternoon.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Red Flag Warning from noon to 9 PM MDT Sunday for East
     Beaverhead.

ID...None.
&&

$$