Big Arm, Montana Weather Forecast Discussion

434
FXUS65 KMSO 180734
AFDMSO
Area Forecast Discussion
National Weather Service Missoula MT
134 AM MDT Thu Sep 18 2025
.DISCUSSION...
KEY MESSAGES:
- Warm, sunny, dry conditions continue through Saturday.
- Westerly winds with gusts 30-40 mph are expected Sunday with
  choppy conditions on area lakes, especially Flathead Lake.
- Chance of showers and thunderstorms Sunday evening, then a
  return to a ridge of high pressure over the region.
The ridge over the region continues to cause sunny skies and
temperatures 10-15 degrees above average through Saturday. With
the longer nights as we are near the Autumn equinox, patchy fog
will continue to form in some of the valleys each morning. Even
some frost is possible in the high elevation valleys.
On Sunday a trough moves across the region. Current model
forecasts are pretty dry and are mainly showing stronger winds
with some isolated showers and thunderstorms Sunday evening. The
chances for measurable rain are about 30-40% in most valleys and
40-50% in the mountains and far northwest Montana. The chances for
wind gusts over 30 mph are 50-70% in the mountains of Montana, and
20-40% at the lower elevations of northwest Montana, including
Flathead Lake. Missoula southward the chances for 30 mph or
greater gusts is only 10-20% with generally 10% or less in Idaho.
After the Sunday trough moves on, the area returns to a stable,
ridge pattern for about a week. Looking at long range ensembles,
there is good consensus for the ridge to break down within a
couple of days around September 27th.
&&
.AVIATION...High pressure continues to dominate the weather for
the region through Saturday. With longer nights to cool off and
dew points in the 40s in most valleys, patchy fog is a concern in
the mornings. Terminals KBTM and KGPI are most likely to be
affected this morning, and so they have mist in their TAFS.
Terminals KHRF and KMSO may have some localized fog near the
river, but it is not expected to impact the terminals this
morning.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&
$$

NWS MSO Office Area Forecast Discussion