529
FXUS65 KMSO 021918
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
118 PM MDT Tue Sep 2 2025

.DISCUSSION...

KEY MESSAGES:

-  Hot and dry conditions through Wednesday with elevated
   HeatRisk

-  Increased easterly winds expected Thursday into Friday

-  Pattern change to showers and thunderstorms begins this weekend

The dominant ridge of high pressure will shift slightly westward
over the next couple of days, amplifying the ongoing heatwave
across the Northern Rockies. This will continue the warming and
drying trend through Thursday. High temperatures, combined with
warm overnight lows, will continue to elevate HeatRisk to moderate
or major levels for the lower valleys of north-central Idaho and
northwest Montanaincluding Riggins, Orofino, Thompson Falls, and
Libby. The current Heat Advisory for Idaho has been extended
through Wednesday evening.

As the ridge of high pressure centers just to our west, a period
of persistent easterly to northeasterly winds will become a
notable change from Thursday into Friday. The increase in east to
northeast winds will create choppy conditions on Flathead Lake by
Thursday afternoon and evening, with a 25 percent probability of
gusts reaching 25 mph between 4 PM and midnight. This wind pattern
also has the potential to transport smoke from wildfires burning
in Alberta and Saskatchewan southwestward into our region. If you
plan to recreate outdoors, keep in mind the potential for
increased smoke and choppy conditions on area lakes.

Looking ahead to the weekend, forecast models continue to indicate
that the ridge will shift eastward, allowing a more southwesterly
flow to develop over the region. This will bring a slight cooling
trend, though temperatures are expected to remain above average
for this time of year. More importantly, this pattern will
reintroduce enough moisture and instability to bring a renewed
chance for showers and thunderstorms. With precipitable water
values ranging from 150% to 200% of normal, combined with light
upper-level steering winds, there is a marginal risk for excessive
rainfall. Recent burn scars and steep, rocky terrain may be at
increased risk for runoff impacts.


&&

.AVIATION...High density altitude and widespread haze will be the
primary focuses through Wednesday. MVFR conditions can be
expected near local fires, especially during the morning hours for
the next 48hrs. Widespread east/northeast winds will develop over
the Northern Rockies Thursday.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Heat Advisory until midnight MDT Wednesday night for
     Kootenai/Cabinet Region...Lower Clark Fork Region.

ID...Heat Advisory until 11 PM PDT Wednesday for Lower Hells
     Canyon/Salmon River Region...Orofino/Grangeville Region.

&&

$$