817
FXUS65 KMSO 150841
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
241 AM MDT Tue Sep 15 2026

.DISCUSSION...

KEY MESSAGES:

- Chilly start this morning across southwest Montana and north
  central Idaho with patchy valley fog.

- Warming and drying through mid week, then wetter Thursday into
  Friday.

Clear skies south of Highway 200 in western Montana and north-central
Idaho allowed temperatures to drop near or below freezing early
this morning, leading to patchy frost and valley fog that may
expand through daybreak. North of Highway 200, cloud cover remains
thicker, keeping temperatures slightly milder. Expect passing
mid- to high-level clouds across the region today, with a few
light, scattered showers remaining confined near the Canadian
border.

Sunny skies and warmer temperatures arrive Wednesday as high
pressure briefly builds over western Montana and central Idaho.

Rain chances return Thursday into Friday as a slow-moving weather
system pulls abundant monsoonal moisture into the Northern
Rockies. While widespread severe weather is not expected,
afternoon heating will trigger scattered thunderstorms. Because
these storms will likely move slowly, the primary hazard will be
intense downpours.

High pressure builds into the Northern Rockies as the low departs
Saturday afternoon, bringing warm and dry conditions through at
least early next week. Confidence remains high for dry weather
through Monday, though approximately 30% of ensemble members show
a cooler, wetter pattern returning by mid-week.

&&

.AVIATION...Patchy valley fog will continue to expand through daybreak
across southwest Montana and north central Idaho (potentially
including terminals like KMSO and KHRF), bringing localized IFR
visibilities and ceilings before burning off around mid-morning.
Farther north toward KGPI, thicker cloud cover will limit fog
development, though VFR mid-to-high level ceilings and isolated
light showers near the Canadian border will persist through the
afternoon. A northerly wind gradient may help to enhance the early
evening north winds at KMSO, and KGPI may experience more
variable wind rather than the typical southerly lake breeze.


&&

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

$$