Polebridge, Montana Weather Forecast Discussion

162
FXUS65 KMSO 211828
AFDMSO
Area Forecast Discussion
National Weather Service Missoula MT
1228 PM MDT Sun Sep 21 2025
.DISCUSSION...
KEY MESSAGES:
- Breezy with showers and thunderstorms this afternoon and
  evening.
- Widespread valley frost possible Tuesday morning, especially
  western Montana
- Warming and drying trend through late week
A cold front is poised to cross through north central Idaho and
western Montana this afternoon, serving as the primary forecast
driver through tonight. Expect widespread showers to accompany and
follow the frontal passage. Gusty southwesterly winds of 20 to 30
mph will develop ahead of the front, shifting to the west/northwest
and remaining gusty this evening. These winds will create choppy
conditions on area lakes, posing a potential hazard to boaters.
Instability will be sufficient for thunderstorm development this
afternoon, with the greatest potential focused south of the I-90
corridor. Any thunderstorms will be capable of producing locally
heavy rainfall and accentuating winds, with gusts potentially
reaching 40 mph.
Post-frontal high pressure begins to build in on Monday, ushering
in a cooler, drier, and more stable airmass. This will lead to
clearing skies and diminishing winds through the day, with high
temperatures returning to near-normal values for late September.
Some smoke from fires in Washington may cause hazy skies,
especially in north central Idaho and west-central Montana.
The first widespread frost/freeze event of the season is
anticipated Monday night into Tuesday morning. With clearing
skies and light winds, strong radiational cooling is expected.
Probabilistic guidance indicates a 50-70% chance of
temperatures falling below 37 degrees in the Missoula/Bitterroot
and northern Flathead valleys. Confidence is higher for a freeze
in the higher valleys of north-central Idaho and near the
Continental Divide (e.g., Butte, Seeley Lake, Elk City), with a
70-80% chance of temperatures reaching the freezing mark or colder
(32 degrees). Residents should take action to protect sensitive
vegetation.
An upper-level ridge will amplify over the region, dominating the
weather pattern for much of the upcoming week. This will result
in abundant sunshine and a significant warming trend, with
afternoon highs climbing into the 80s by mid-week (roughly 10 to
15 degrees above seasonal normals). The strengthening ridge and
development of a stable airmass will also likely trap smoke/haze,
potentially degrading air quality in valley locations at times.
Toward the end of the work week, guidance suggests some flattening
of the ridge, which could lead to an increase in winds. However,
ensemble guidance shows considerable spread in the day 7-10
period, resulting in low forecast confidence for next weekend.
Solutions diverge significantly, with various members supporting a
persistent ridge, a transition to southwest flow with increased
moisture (thunderstorms?), or the arrival of a cooler trough.
&&
.AVIATION...A cold front will be moving across the region today.
Showers and thunderstorms are possible generally from Polson (30%
chance) southwards to Lemhi County (50% chance), and northeast to
BTM (50% chance) this afternoon and evening. General westerly
winds, gusting over 25 knots, will increase this afternoon through
early evening as the cold front moves through. Between 7 pm and
11 pm MDT this evening (22/0100UTC to 0500UTC),there is a 35%
chance for thunderstorms across Lincoln County in northwest
Montana. Depending on how fast the clouds clear out, there could
be lower ceilings and/or patchy fog from SMN to BTM Monday
morning. Latest wildfire smoke projections depict possible
increase across north- central Idaho into west-central Montana
late tonight through 22/1700z (11 am MDT Monday). Expect to see at
least some haze in the mountains in these areas.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&
$$

NWS MSO Office Area Forecast Discussion