577
FXUS65 KMSO 211959
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
159 PM MDT Thu Aug 21 2025

.DISCUSSION...

KEY MESSAGES:

- Increasing chances for locally degraded air quality through the
  weekend due to increased wildfire smoke and stable conditions

- Heat this weekend

- Increasing chances for thunderstorms Sunday into early next
  week as monsoonal moisture approaches the region from the
  southwest

Flat westerly flow aloft today and tomorrow will bring seasonably
warm temperatures and little to no chance for thunderstorms as
much drier air has settled into the region. Locally degraded air
quality is anticipated as new local wildfires continue to get
active each afternoon.

Later tonight into Friday, a backdoor cold front moving through
north central Idaho will increase northeasterly flow at the
surface. The cooler temperatures will remain east of the divide,
but breezy easterly winds will be noticeable, especially in
western Montana. High resolution models show that this easterly
gradient will concentrate wildfire smoke in north central Idaho,
potentially bringing poor air quality into areas such as the Camas
Prairie, Grangeville, and portions of the Highway 12 and 95
corridors.

High pressure will strengthen through the weekend, bringing a
warming trend in temperatures. Heat advisories may be needed for
the lower valleys of north central Idaho where daytime
temperatures will reach into the 100s and nighttime temperatures
may not drop out of the 60s. The one possible limiting factor will
be smoke concentrations, which may keep temperatures from reaching
full heating potential.

Forecast models continue to show the potential for monsoonal
moisture to work northwards out of the desert southwest by the end
of the weekend into early next week. This moisture feed will bring
increasing chances for thunderstorms, first across southwest
Montana and Lemhi County, then possibly reaching as far north as
the Mission valley in Montana by Wednesday.

&&

.AVIATION...Fair flying conditions are expected with the exception
of impacts from smoke due to local wildfires. KSMN will continue
to experience reduced visibility due to smoke, though some
improvement is likely later this afternoon and evening. An
northeasterly wind gradient will develop overnight tonight and
strengthen across western Montana through Friday morning.
Northeast to east winds of 10 to 15 kts will be common. This will
help improve smoke conditions for some, but high resolution
models show smoke concentration through north central Idaho, which
may cause additional limitations to ceiling and visibility,
including for KGIC.

&&

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

$$