943
FXUS63 KDMX 201057
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
557 AM CDT Sun Sep 20 2026

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Showers and thunderstorms are moving out of the area and will
  continue to move out through the morning.

- Areas of patchy fog are possible before sunrise, mainly north
  of I-80.

- More autumnal conditions expected today with cooler
  temperatures and drizzle throughout the day with the potential
  for more widespread showers and storms overnight into Monday.

- Cool temperatures and moist weather persist into Monday, with
  drier conditions expected Tuesday and Wednesday.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 253 AM CDT Sun Sep 20 2026

Showers and thunderstorms are ongoing across portions of central and
eastern Iowa. Areas to the north of the showers and storms are
currently experiencing patchy fog per the nighttime microphysics
satellite band as a moist airmass remains over the region. The
showers and storms are being fueled by the Low Level Jet (LLJ) which
will both weaken and take on a less favorable orientation closer to
sunrise. At the same time, the expansive high pressure that has been
pancaked over the southern US has begun to break down, leading to
meager flow at 850mb, which means low-level moisture transport into
the region is going to be substantially reduced. Furthermore, the
breaking down of this high combined with a weak mid-level low
forming over the western plains means mid-level moisture transport
will be favored better south of Iowa. While this doesn`t lead to a
completely dry forecast for the next couple of days, it does lead to
a day with lowered concerns for heavy rainfall once our current
showers and storms exit the area. As for rainfall amounts through
the morning, with some of the heavier bands it looks like 1-2 inches
of rainfall is expected with a few pockets closer to 3 inches. The
axis of heaviest rainfall with this activity remains to our east.

Once the ongoing showers and storms exit the area, much more
autumnal conditions are expected. Behind a cold front which will
help usher out the remaining showers, northerly flow will persist as
high pressure builds over Ontario. This leads to highs generally in
the 60s across much of the state with areas in far southern Iowa
approaching 70. While a moist airmass is already in place,
northeasterly moisture transport in the low levels will help keep
much of the atmosphere just above the surface saturated enough for
low stratus clouds and drizzle. Sounding profiles show a saturated
airmass up to about 800mb across the state. Some soundings show
there is very minimal CAPE, leading to the potential for a proper
shower or two, but values are low enough (<500 J/kg) that widespread
convection is not expected.

While drizzle will persist through the day, conditions for it remain
favorable into the overnight before another disturbance moves into
the area. A weak low over the Nebraska panhandle will develop. Weak
Theta-E advection will allow for more widespread showers and
thunderstorms to be kicked off, mainly in western and northwestern
Iowa overnight into Monday morning. Weak shear (25kts or less) and
limited instability (<500J/kg) lead to the only concern being a few
rumbles of thunder with stronger storms.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 255 PM CDT Sat Sep 19 2026

The cooler, fall-like conditions continue into Monday and early next
week with highs generally only reaching the upper 50s to near 60
both Monday and Tuesday. Our light rain generally continues into
Monday, this time with a bit more synoptic support as a an upper
level low meanders into Iowa trudging along in the zonal upper level
flow. This low hangs out overhead into Tuesday, but begins to
bring drier air into the state. Should this pan out as the
models suggest, we should finally see a few dry days Tuesday and
Wednesday of next week. However, rain chances do look to return
to at least western Iowa on Thursday. More details on that in
the coming days.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 550 AM CDT Sun Sep 20 2026

IFR to MVFR conditions are expected around the state due to low
ceilings throughout this TAF period. Conditions today are
favorable for drizzle before 18z/1pm, although low confidence
in persistence at any one location has led to PROB30 mentions at
KALO, KFOD, KDSM, and KOTM. Visibility reductions are possible,
but without a good measure of the magnitude of visibility
reductions, the PROB30 groups are left at 6SM. Otherwise, winds
will be breezy (10-15kts) from the northeast with gusts as high
as 22kts possible at times, especially in the north.

&&

.HYDROLOGY...
Issued at 312 PM CDT Sat Sep 19 2026

The moisture rich environment overhead will bring yet another night
of heavy rain potential to the state, this time central into
southern and eastern Iowa. The weather prediction center has placed
a moderate risk (level 3 of 4) for excessive rainfall to our east,
while most of the DMX forecast area resides in a slight risk (level
2 of 4) or a marginal risk (level 1 of 4). Most of the precipitation
expected tonight will develop with the low level jet oriented
roughly parallel to the boundary, supporting some training storms
and potential for prolonged moderate to heavy rainfall. However, CAM
guidance suggests storms could be fairly progressive, rather than
camping over one area for a long period of time. Likewise, HREF for
1" per hour rates are near-zero, likely thanks to the waning
instability by the time these storms develop. QPF output generally
ranges from 1 to 2" with some pockets getting closer to 3" in a few
models. While this could lead to some ponding issues, or even minor
flash flooding should one of the 3" bullseyes align with an urban
area, have decided to hold off on a Flash Flood Watch at this time.
With the low probability for 1" per hour rates and potential
progressive nature of the rainfall, confidence isn`t high enough at
this time.

As for river flooding, heavy rain in Minnesota last night has
resulted in responses on rivers upstream from the Cedar River basin.
As a result, water routing down through these basins will likely
lead to rises into action stage early this week along the Cedar
River, specifically ALOI4 and CEDI4. At this time, flooding is not
expected and any additional rainfall today and tonight should fall
south and east of these rivers basins. However, upstream
observations will be monitored closely as water routes into the
rivers and information will be provided should anything change.

For tonight, rainfall amounts of 1 to 3" should generally only cause
in-bank rises for most rivers. That said, a few rivers are running
at elevated levels from rains earlier this week, namely the North
River near Norwalk (NRWI4) and Des Moines River at Ottumwa (OTMI4).
Should these basins get hit with prolonged heavy rain tonight,
additional rises are certainly possible.

&&

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

&&

$$

SHORT TERM...67
LONG TERM...Dodson
AVIATION...67
HYDROLOGY...Dodson