Duncan, Iowa Weather Forecast Discussion

298
FXUS63 KDMX 071851
AFDDMX
Area Forecast Discussion
National Weather Service Des Moines IA
151 PM CDT Sun Sep 7 2025
.KEY MESSAGES...
- A few sprinkles are possible in northern Iowa late tonight,
  then shower and thunderstorm chances (20-30%) return to the
  forecast at times from Monday night into Tuesday night.
- Notably warmer weather will build in later this week, with
  daily high temperatures well into the 80s from Wednesday
  onward. Rain chances will return again next weekend.
&&
.DISCUSSION...
Issued at 151 PM CDT Sun Sep 7 2025
A surface high pressure area currently covers Iowa and
neighboring states, resulting in relatively cool and sunny
conditions with light and variable winds. The high pressure will
move away to the east tonight and Monday, bringing low-level
winds around to southeast then south by Monday afternoon. A
broad low pressure trough will also develop along the lee of the
Rockies during this time, and between 850 MB and 700 MB a band
of modest warm air/moisture advection will move from
northeastern Nebraska over to and along the Iowa/Minnesota
border region overnight tonight. While most CAMs depict
scattered light radar reflectivity echoes associated with this
feature, corresponding QPF fields are zero and forecast
soundings show the column remaining quite dry overall, including
a substantial dry layer between the surface and any cloud bases,
not to mention a lack of instability and only nebulous forcing.
Given this environment, it is likely that precipitation will be
difficult to generate, and even if it does occur would likely
evaporate before reaching the surface. Have introduced just a
chance (30%) of sprinkles across our northern counties late
tonight/early Monday morning accordingly.
During the day on Monday a broad and fairly weak 500 MB trough
will move eastward over the High Plains, then slowly cross Iowa
Monday night through Tuesday. As this trough approaches, HRRR
Vertically Integrated Smoke indicates a large area of elevated
smoke from distant fires will spread over the region from late
Monday into Tuesday, however, the aforementioned trough will
also result in partly to mostly cloudy skies during this time so
any degree to which smoke aloft will be visible is limited, and
in any event it is unlikely to reach the surface. In addition,
the approach and passage of the trough has been consistently
generating light QPF across our forecast area from late Monday
into Tuesday night, however, now that the time is approaching
the high-res models are really backing off on this, and once
again it would seem dry air in the column is the primary
limiting factor. There is some minimal instability in western
Iowa, where MUCAPE is forecast to peak below 1000 J/kg late
Monday, but moisture is likely too paltry to support
precipitation in the absence of stronger forcing or instability.
Have thus gone with a dry forecast through Monday afternoon. As
the trough moves slowly through between Monday night and
Tuesday night, gradual moistening of forecast soundings will
allow for some showers and a few thunderstorms, and have
maintained chance (30-50%) PoPs during this period. However,
instability and shear are far too limited to support a severe
weather threat and little to no impact is anticipated.
In the latter part of this week, generally between about
Wednesday and Friday, a large 500 MB ridge will build across the
Midwest. While some model solutions attempt to generate spotty,
light QPF during this time, large-scale subsidence would appear
to dampen such hopes and have continued a nearly dry forecast,
with only occasional patches of 20% rain chances. This period of
ridging will also promote even warmer temperatures. After highs
generally around 75-80 degrees Monday and Tuesday, they will
range well into the 80s from Wednesday through Friday and may
even reach 90 degrees in a few southern Iowa locations at the
end of the week. By next weekend a large 500 MB low will
develop over the northern Rockies or thereabouts and may support
a return of rain chances and somewhat more active weather to
Iowa, but model variability is high and confidence in such
details very low at this range.
&&
.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1225 PM CDT Sun Sep 7 2025
VFR conditions are expected through the 18Z TAF period, with no
aviation impacts.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
DISCUSSION...Lee
AVIATION...Lee

NWS DMX Office Area Forecast Discussion