Marshalltown, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

012
FXUS63 KDMX 052243
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
543 PM CDT Fri Sep 5 2025

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- A few sprinkles or light showers possible north and northeast
  late today, otherwise the forecast is dry through the weekend.

- Cool weather persists for a couple more days. Sunday morning
  low temperatures in the upper 30s across part of northern and
  western Iowa.

- Warming next week, with rain chances returning intermittently
  (40-60% chance around Monday night, otherwise lower than 30%).

&&

.DISCUSSION...
Issued at 138 PM CDT Fri Sep 5 2025

A large cyclone is currently parked over Ontario, with its
cyclonic flow extending down across the Upper Midwest. A lobe of
vorticity is evident in water vapor satellite imagery, crossing
South Dakota and headed toward northern Iowa this afternoon and
evening. Visible satellite imagery shows a large field of
diurnally generated stratocumulus clouds, covering much of the
region and enhanced by modest low-level cold air advection. As
the vorticity lobe swings overhead later today and provides some
mid-level lift, it may be sufficient to generate a few
sprinkles or light showers mainly in our northern counties.
However, forecast soundings illustrate most of the associated
lift will occur above the cloud layer, and the moisture is quite
shallow so any precipitation that does occur will likely be
very light and may not even reach the ground. Indeed, regional
radar imagery depicts a few light echoes approaching the
SD/MN/IA tri-state area, but so far no precipitation has
registered at surface observing sites beneath these returns.
Nevertheless, with the possibility of slight enhancement as the
afternoon progresses and in the interests of consistency, will
maintain the slight chance (20%) of showers forecast in our
north and northeast late this afternoon and evening. In any
event, no impacts are anticipated.

From tonight onward the Ontario gyre will begin to move off
slowly to the east, gradually weakening the cyclonic flow over
Iowa. Another lobe of vorticity will round the southwestern
periphery of the system again on Saturday, but farther northeast
than today with any associated showers more likely over
Wisconsin or far northeastern Iowa, so the forecast remains dry
for our service area. Concurrently, a ridge of surface high
pressure will build into Iowa from the northeast on Saturday
night and remain overhead on Sunday. This will result in light
winds and mostly clear skies, with temperatures falling to their
lowest point of the week on Sunday morning but then rebounding
by Sunday afternoon to levels higher than those seen the
preceding couple of days. The current forecast calls for lows in
the upper 30s across parts of northern and western Iowa Sunday
morning, with highs ranging in the mid 60s to lower 70s across
Iowa by Sunday afternoon.

From Monday through most of next week a synoptic pattern change
will occur, with roughly zonal 500 MB flow over Iowa on Monday
while a broad ridge develops over the Rockies. A weak trough
will dig over the Midwest around Monday night after which the
larger ridge will slowly traverse the central U.S. during the
latter half of the week. Long-range models show significant
variance in their depiction of the strength of the ridge, as
well as the timing and nature of various subtle impulses moving
through or over it during this time frame. The result is
intermittent, generally low (20-30%) rain chances next week, but
with little in the way of large or strong storm systems
foreseen at this range. The best chance for rain and
thunderstorms (40-60%) will come from around Monday night into
Tuesday in association with the aforementioned trough coming
overhead, but even then it appears instability and shear will be
modest. Temperatures will also be milder in this scenario, with
daily highs likely in the mid-70s to mid-80s for much of the
week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 543 PM CDT Fri Sep 5 2025

High confidence in VFR conditions prevailing through the period
at all terminals. VFR ceilings as low as FL050 will dissipate
this evening, but will see VFR cumulus redevelop as low as FL045
by Saturday late morning through the afternoon. Winds from the
northwest will become light and more from the west overnight
before turning breezy around 10 knots late Saturday morning into
the afternoon.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Lee
AVIATION...Ansorge