347
FXUS65 KMSO 010643
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
1243 AM MDT Tue Sep 1 2026

.DISCUSSION...

KEY MESSAGES:

-  Widespread showers and thunderstorms this afternoon and
   evening, with gusty outflow winds of 30-50 mph, brief moderate rainfall,
   and lightning, strongest storms south of Highway 200.

-  Another round of storms Wednesday capable of 30-50 mph outflows
   and heavy rain rates up to 0.5 inches per hour.

-  Persistent active pattern late week into the weekend under
   southwesterly flow, with a 15% chance of a tropical moisture
   tap on Sunday or Monday.


Today & Tonight: High pressure ridging transitions to
southwesterly flow today, driving afternoon temperatures roughly
10 degrees above normal. Conditions will deteriorate this
afternoon as an atmospheric disturbance lifts northward out of
Lemhi and southern Idaho counties into western Montana, triggering
widespread showers and thunderstorms. The strongest convective
activity is anticipated south of Highway 200 in western Montana,
where storms will be capable of producing gusty outflow winds of
30 to 50 mph, frequent lightning, and brief moderate rainfall.
Activity will taper off and exit the forecast area by midnight.

Wednesday through Weekend: A stronger disturbance will traverse
the Northern Rockies on Wednesday morning-mid afternoon, renewing
the threat for gusty outflow winds of 30 to 50 mph. Heavy
rainfall potential will be enhanced with this second wave, where
stronger storm cores may produce rainfall rates up to 0.50 inches
per hour. Additionally, extreme southwest Montana will contend
with gusty winds and low afternoon relative humidity Wednesday
afternoon and evening and again Thursday, potentially creating
critical fire weather conditions.

Southwesterly flow aloft will persist Thursday into Friday as a
broad upper-level trough settles over the Pacific Northwest. This
pattern will keep temperatures near to slightly below late-summer
averages alongside periodic showers and thunderstorms,
particularly during peak afternoon and evening heating. Guidance
remains in solid agreement that troughing will linger over the
region through the weekend, with roughly 15% of ensemble members
indicating a potential tap of significant tropical moisture Sunday
or Monday. Regardless of whether this tropical plume
materializes, the Northern Rockies will remain embedded in an
active, unsettled weather pattern through the weekend.



&&

.AVIATION...Convective initiation is expected over central Idaho
early this afternoon, with storms tracking northeast into western
Montana through mid- evening. Primary operational hazards include
frequent lightning and erratic outflow winds of 25-45 kt.
Although convective instability diminishes northward toward the
I-90 corridor, linear storm organization will likely sustain
strong outflow boundaries pushing into I-90 terminals and
potentially into northwest Montana. Showers and isolated
thunderstorms may linger through late evening.

By 12Z Wednesday, high-resolution guidance indicates a secondary
wave of convection initiating across southwest Idaho and lifting
northeast across the Northern Rockies through mid afternoon.
Outflow winds of 30-45 kt will once again serve as the primary
aviation hazard.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Fire Weather Watch from Wednesday afternoon through Wednesday
     evening for East Beaverhead.

ID...None.
&&

$$