164
FXUS63 KDMX 181743
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1243 PM CDT Sat Oct 18 2025

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- Patchy fog early this morning across central Iowa

- Showers move across the area this afternoon into tonight with
  breezy northwest winds.

- Cooler Sunday into next week with highs in the 60s.

&&

.UPDATE...
Issued at 249 AM CDT Sat Oct 18 2025

Patchy fog has developed across parts of central Iowa early this
morning, due to available low level moisture, clear skies behind the
line of precipitation, and cooling overnight. Webcams across the
area show the fog fairly patchy in nature. This will be watched
closely for expansion through the morning in case an SPS or
advisory is needed.

Much of today will be mild and quite. By this afternoon a
reinforcing lobe of vorticity sinks south across the area, tapping
into the plume of moisture to the south and east as it moves across
the area. Precipitation will begin across northwest Iowa as
scattered showers. As it moves east this will phase with the parent
trough axis and moisture plume, allowing for more widespread
precipitation central and east through the evening. With very little
instability, severe storms are not forecast and lightning will
be limited. Along and behind the precipitation winds shift to
out of the northwest and increase with subsidence and cold air
advection. Winds may gust 25-30+ mph.

Sunday will be dry and cooler with highs in the low 60s. Winds
remain breezy to start, gradually easing through the day. With dry
air in place relative humidity falls to around 30%. This may result
in increased agricultural fire concerns, however rain Friday
and Saturday should help to mitigate most of these concerns.

&&

.DISCUSSION...
Issued at 243 PM CDT Fri Oct 17 2025

Surface map analysis this afternoon depicts a deepening surface low
pressure system that is centered over North Dakota into Southern
Canada, with a weak front indicated by a southwest to west wind
shift that is oriented from roughly Forest City to Audubon.
Southerly/southwesterly flow remains established overhead, with warm
air advection keeping the warmer temperatures into the state as
values reach through the mid 70s to low 80s ahead of the front, and
in the upper 60s to low 70s behind it. This increase in flow and a
somewhat tighter pressure gradient ahead has brought about continued
breezy conditions as well, with gusts around 20-30 mph that will
continue into the afternoon before decreasing tonight. Along and
ahead of the aforementioned boundary, a line of showers with
embedded weak storms have recently developed, moving northeast
across central Iowa. Limited instability and forcing this afternoon
should keep any storms below severe limits, but storms may continue
at times with the shower activity into the remainder of the
afternoon, with the front stalling near to just east of I-35.
Guidance still indicates that an increase in moisture and better
forcing by early evening should allow for additional and more
scattered development of showers and storms largely over
southern/eastern Iowa. CAM guidance continues to indicate
instability increasing up to 500-1000J/kg of MUCAPE, along with
shear of 30+ knots ahead of the boundary over southeast Iowa that
could result in some stronger storms, though lapse rates are less
supportive. Therefore, the severe risk is low but cannot completely
rule out a strong storm or two with this evening activity, with
small hail and some gusty winds possible.

Showers and weak storms are expected to continue but gradually
decrease in coverage over south/east Iowa through the morning as the
low level jet activity weakens, with a brief period of dry
conditions across much if not all of the state into the afternoon.
However, the boundary will generally remain over southeast Iowa,
which will lead to a noticeable difference in temperatures across
the state, with values in the 60s to low 70s over the northwest half
of the state, and in the mid to upper 70s further southeast. Winds
will be breezy again out of the northwest with gusts up to 20-30
mph. A rather potent lobe of energy within another shortwave trough
pivoting into the Upper Midwest from the larger scale circulation is
expected to drop into Iowa into Saturday evening, paired with
moisture return that is expected to bring additional chances
(20-50%) of light shower activity into the state. Storms are not
expected given very little instability overhead.

The aforementioned trough deepens further as it becomes negatively
tilted into Sunday morning, which will develop a rather strong low
pressure system into the Ohio Valley, extending a cold front
through Missouri where enhanced forcing will lead to a large
area of showers and storms in that area. Trends remain in the
decreasing potential for this to backbuild into far eastern Iowa
per latest guidance, which will lead to drying conditions into
Sunday overhead. A notable push in cold air advection and drier
air from northwesterly flow will continue Saturday evening into
Sunday, with upper level ridging building across the
northwestern CONUS that will quickly move across the Midwest.
Highs will be more seasonal with values in the 60s across Iowa,
along with breezy conditions. Low RHs in the upper 20s to low
30s with the breezy winds could lead to at least some potential
for elevated fire weather conditions Sunday. Dry conditions
remain into the start of the work week with highs in the upper
60s to low 70s, before the next trough dropping into the Midwest
from Canada drops a frontal boundary into the region by Monday
evening. Per NAM guidance, weak lift and moisture into eastern
Iowa is suggested that would bring another chances for showers,
with the GFS indicating activity from this feature mainly over
northeast Iowa while the Euro has more widespread coverage
across Iowa. These differences are still expected given this is
several days out, but seem to agree on at least eastern Iowa
seeing rainfall so have left chances (<20%) there at this time
and will update as new data comes in. Regardless, the frontal
passage will result in cooler temperatures in the upper 50s to
low 60s. Upper level northwest flow then seems to settle at
least through midweek, keeping conditions generally on the dry
side with high pressure over the region as temperatures remain
in the 60s through Thursday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1240 PM CDT Sat Oct 18 2025

An area of showers and perhaps isolated thunderstorms will move
across central Iowa late this afternoon over the northwest and
over the rest of the area overnight. Cigs will remain mainly VFR
but local MVFR may occur. Vsby restrictions in rain may occur.
The period of rain at sites will range from 2-4 hours. Gusty
north winds will develop as well later this afternoon and
overnight. Expect clearing late tonight and into Sunday.

&&

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

&&

$$

UPDATE...Hagenhoff
DISCUSSION...Bury
AVIATION...Donavon