762
FXUS65 KMSO 292023
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
223 PM MDT Mon Sep 29 2025

.DISCUSSION...

KEY MESSAGES:

-  Strong, gusty outflow between 35 and 45 mph, are expected from
   showers and thunderstorms. Lightning and downpours possible
   with heavier cores Bitterroot to Butte.

-  0.25" to 0.50" of rainfall possible along US-93 corridor Olney
   to Salmon, Idaho through Tuesday evening. Other places not so
   lucky..i.e. Lincoln County, southwest Montana towards Butte.

-  Seasonable Fall weather arrives this week. Jackets may be
   needed at times. Depending on cloud cover, sub-freezing
   mornings possible late week.

-  60% chance for mountain snowfall next weekend; 50% chance for
   at least 2 inches of snow along Divide mountains.

Satellite imagery early this afternoon depicts a vast amount of
cloud cover across the Pacific Northwest into north-central Idaho.
Much of western Montana and Lemhi County are warming up into the
70s, on their way to the low 80s. An elongated line of showers
extends from southwest Idaho north towards Grangeville and western
Clearwater County. This is likely near the surface cold front
boundary that is expected to shift eastwards with time later
today. The areas that saw the sun today will have the most
instability for thunderstorms...CAPE values range between 100 and
300 J/kg, but if you factor in the relative dryness of the
atmosphere, strong gusty winds are anticipated. High resolution
models depict the higher probabilities for 35 to 45 mph winds
extending from the Bitterroot Valley north and east this afternoon
into the evening hours. Storms forming off the southern
Bitterroot mountains may congeal into a line that tracks
northwards, possibly impacting areas north of Missoula towards
Flathead Lake between 6 and 9 pm MDT. Heads` up if you are
planning on recreating on the lake during this timeframe.

Among the disturbances embedded in the cyclonic flow over the
Pacific Northwest, a more organized wave will bring another round
of light to moderate showers to the region tonight. These showers
will linger Tuesday morning from northwest Montana to west-central
Montana, so a rain jacket may be needed at the bus stops.

It will feel cooler on Tuesday and Wednesday, but still a few
degrees above average for this time of year. Scattered showers
will be possible at times during the day and nighttime hours,
depending on shortwave activity. This unsettled pattern continues
throughout the remainder of the week. If clouds are able to clear
enough Thursday and Friday nights, then low-lying locations could
be susceptible to sub-freezing temperatures.

Models are consolidating on more of a deeper trough developing
over the region by this weekend. This is a pattern conducive for
gusty northeast winds, and snowfall down to mountain passes along
the Continental Divide. Snow levels could be as low as 5000 feet
MSL. We could be looking at temperatures 10 to 15 degrees colder
than average! The latest NBM gives us around a 60 percent chance
for at least 0.1" of snow to fall across the western Montana
mountains by next Sunday. For 2 inches or greater, the probability
is around 50 percent and more localized over the Divide.

&&

.AVIATION...A significant pattern change is underway this
afternoon as a Pacific trough drives southerly flow and increasing
moisture into western Montana and north-central Idaho.
Instability and widespread lift will generate showers and
thunderstorms, with peak activity anticipated between 29/2200z and
30/0300z. Relatively dry air at the surface will create an
environment favorable for high- based thunderstorms, making strong
outflow gusts up to 40 kts the primary threat, particularly for
areas from Flathead Lake southward to the Bitterroot Valley. In
addition to the wind, these storms may also produce brief heavy
rain. Airfields KSMN and KHRF have the highest potential for
thunderstorms. This activity marks the beginning of the shift to a
wetter pattern, as shower and thunderstorm coverage is expected
to expand and become more widespread tonight into Tuesday morning.
Anticipate obscurations of the higher terrain to increase due to
lowering clouds cover and rain Monday afternoon into Tuesday
morning. Another round of scattered showers and isolated
thunderstorms are expected on Tuesday afternoon.

&&

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

$$