Heron, Montana Weather Forecast Discussion

331
FXUS65 KMSO 270918
AFDMSO
Area Forecast Discussion
National Weather Service Missoula MT
318 AM MDT Sat Sep 27 2025
.DISCUSSION...
KEY MESSAGES:
- Warm and dry conditions this weekend with hazy skies due to
  wildfire smoke
- Pattern change to cooler and wetter next week
An amplifying upper-level ridge of high pressure will produce unseasonably
warm and dry conditions this weekend. Temperatures will climb back into the
low 80s for many valleys, which is roughly 10 degrees above normal for this
time of year. Sunday is expected to be the warmest day.  Lingering wildfire
smoke will create hazy conditions, with forecast models showing northwest
Montana seeing the most smoke due to southwest flow aloft ushering smoke in
from Washington.
A significant pattern change is expected early next week as a cool, moist
Pacific trough replaces the ridge. On Monday, increasing southwesterly flow
will advect moisture aloft over a dry low-level airmass. This setup favors
high-based convection capable of producing strong outflow winds up to 50
mph, primarily across north-central Idaho and into west-central Montana
south of I-90.
By Tuesday, a deeper moisture profile will increase the coverage and
efficiency of showers and thunderstorms. The primary threat will transition
from strong winds to locally heavy rainfall. The highest confidence for
beneficial, wetting rains is over north-central Idaho and the mountains of
western Montana. An elevated risk for excessive runoff or flash flooding
will exist near burn scars and in steep terrain.
Considerable uncertainty exists for the late-week period, centered on the
evolution of the upper low. A majority of global model ensemble members
(~60%) favor the de-amplification of the trough, which would lead to a dry
and breezy westerly flow aloft. Of the remaining solutions, a significant
minority (~25%) maintain a cooler, unsettled pattern through the weekend,
while a smaller contingent (~15%) indicates a faster transition to
rebuilding high pressure. This spread denotes low confidence in the
forecast beyond Thursday.
&&
.AVIATION...High pressure will maintain generally clear skies, warm
daytime temperatures and light/terrain driven winds through the
weekend. Wildfire smoke will cause hazy skies and may locally
lower visibility, particularly across northwest Montana.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&
$$

NWS MSO Office Area Forecast Discussion