717
FXUS63 KDMX 221855
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
155 PM CDT Tue Sep 22 2026

.KEY MESSAGES...

- Drizzle and fog continue to diminish from northwest to
  southeast over central Iowa through late today.

- Brighter skies, but still cool on Wednesday.

- Showers and occasional storms return from west to east
  Thursday or Friday before drier air arrives on Sunday.
  Conditions remain cool through first half of weekend.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 155 PM CDT Tue Sep 22 2026

The lead shortwave trough is moving toward Lake Michigan early
this afternoon as evident on GOES-East upper level water vapor
imagery. This has pulled most of the very spotty showers that
were over our southeastern forecast area into eastern Iowa.
However, clouds will remain through the day as low level
saturation persists in the lowest 2km. Areas of drizzle and
patchy fog will persist beneath these clouds in this
saturation through at least this afternoon as it ends from
northwest to southeast across central Iowa. The drizzle may
need to be extended further into tonight given that RAP
soundings show the saturation continuing until around midnight.
The drier air does eventually arrive, albeit slowly, as the
trailing shortwave trough moves through the state and high
pressure influence noses in from the east finally. Despite the
drier air moving in, relative humidity remains high and low
chances of light fog remain, which is shown in the NBM and GFS
MOS guidance. Forecast soundings show no full saturation at the
surface so will forgo any fog mention at this time. However, if
the sky does clear, this may increase fog chances and in
addition may result in temperatures falling lower than forecast,
such as northeastern Iowa into the low 40s.

With the drier air pushing westward through the morning
Wednesday, skies will turn brighter first in eastern parts of
our forecast area and then in western parts by midday
Wednesday. Cross sections persist a thinning layer of low level
moisture such that cumulus clouds may develop in the afternoon -
particularly over eastern Iowa/along and east of I-35. This
moisture will be beneath a ridge axis that will poke up into
Siouxland at least keeping conditions dry through the day.
However, a shortwave trough lifting northeastward will tamp back
down the ridge and bring a return of higher atmospheric
moisture into the state. Further, a ribbon of modest QG
convergence will spread over western into central Iowa with a
few pulses of theta-e advection. This will prompt scattered
showers and storms to arrive over western Iowa in the early
morning hours of Thursday. At this time, these may be confined
to mainly the western half of the state through the day where
the stronger forcing will reside along with light, southeasterly
flow that will funnel in low level drier air from surface high
pressure over the Great Lakes. The low level jet pointed into
eastern Nebraska will keep scattered showers and storms going
over the western part of the state Thursday evening, but as that
veers toward Iowa late Thursday night/early Friday morning this
activity may start to spread farther eastward into the state.
Severe weather is unlikely given weak instability and lapse
rates, though efficient rainfall may be possible with high
precipitable water values and deep warm cloud depths.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Issued at 155 PM CDT Tue Sep 22 2026

Intermittent showers and storms will persist Friday into Saturday as
low level QG convergence and theta-e advection slowly move eastward.
While it will not be days full of rainfall, the days will be more
common to the ones we have had recently with plenty of clouds and
times of precipitation. While there will be instability for
occasional storms, the higher instability and overlapping shear
is displaced west of the area. Thus, locally heavy rainfall
continues to be the main concern due to the antecedent wet
conditions. While soils will have a 24 to 48 hours break with
dry conditions, infiltration capacity will remain reduced along
with elevated streamflows. Rainfall totals still look on track
between 1 and 3 inches on the high end with ensemble
probabilities of a 1" of rainfall in 24 hours between 45 and 55%
over western Iowa Friday morning into Saturday morning
dwindling to 20 to 30% chance over central Iowa Saturday morning
through Sunday morning. A break in the rainfall will arrive as
another shortwave trough lifting northeastward or eastward moves
through the region. This should bring large scale subsidence
into the area on Sunday providing drier conditions that may last
into at least Monday. Temperatures late this week into early
this weekend will remain on the cool side.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1202 PM CDT Tue Sep 22 2026

Widespread clouds with IFR and low end MVFR ceilings will be
common through this afternoon, but ceilings will trend upward
tonight with VFR conditions expected over the eastern terminals
this evening and the western terminals by around midnight.
Drizzle and/or patchy fog this afternoon is expected to
dissipate through the afternoon; however, it is possible light
fog may try to develop toward sunrise. Confidence is low in this
potential so it is not included at this time. Further, may see
scattered cumulus clouds developing by the end of the period
over the eastern terminals due to lingering low level moisture,
which is shown by the FEW025-FEW040 ceilings.

&&

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

&&

$$

SHORT TERM...Ansorge
LONG TERM...Ansorge
AVIATION...Ansorge