881
FXUS63 KDMX 300837
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
337 AM CDT Wed Sep 30 2026

.KEY MESSAGES...

- Rain continues this morning and through much of the day today.

- A reinforcing push of rain and thunderstorms arrives later
  this afternoon and evening, bringing heavy rain and flash
  flood potential. The prolonged rainfall and already saturated conditions
  may lead to river flooding as well.

- Rain and storms diminish from northwest to southeast through
  the day on Thursday, giving way to cooler and drier conditions
  into the weekend.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 333 AM CDT Wed Sep 30 2026

"Soggy" feels like a fitting word to describe the weather in Iowa
early this morning (and really through the next 24 to 48 hours), as
much of the state is either experiencing a light to moderate rain or
patchy fog from moisture leftover from rains earlier in the night.
Rain amounts as of 2 AM from personal weather stations show an
average of about a half an inch of rain, albeit with multiple swaths
of relatively higher amounts in the 1 to 2 inch range. We are seeing
a lull in rain activity over northern into central Iowa, with much
of the rain only occurring in southern and eastern Iowa at this
time. In the areas no longer raining, visibilites around 3 to 6
miles are being reported from patchy fog/mist.

Through the morning, steady rainfall will continue over south
central Iowa with a subtle northward progression. An 850 mb low
level jet will keep a steady stream of moisture pointed into the
area, accompanied by a swath of increased deep moisture convergence.
Eventually, this activity will be reinforced by the approaching
remnants of Hurricane Polo, which are now being ejected out ahead of
the southern stream 500 mb trough and sit roughly over the
Texas/Oklahoma panhandle region. This secondary plume of moisture
and lift looks to first arrive in southwest Iowa around 21 to 00z
today, fusing with the already moisture rich environment overhead
and bringing rain and thunderstorms to the area through tonight into
Thursday. Forecast PWATs of 2.00 to 2.10" will be well above the
climatological daily max (1.61") for this time of year, and storm
motions overnight will be roughly parallel to the SSW to NNE
oriented stationary boundary, resulting in efficient rainfall and
high forecast rainfall amounts.

Most of guidance continues to show a broad area of 1 to 3" falling
over much of central into southern Iowa by mid-day Thursday, with
deterministic guidance indicating there could be embedded swaths of
higher amounts nearing 5 to 6 inches. These swaths will coincide
with higher rainfall rates/convective processes and training storms,
bringing an increased potential for flash flooding. This QPF axis
has moved around quite a bit over recent shifts, ranging anywhere
from northwest Iowa a 2 days ago, to south central Iowa yesterday,
and is now seeing a slight retreat back northward, placing it
roughly from Highway 30 southward. Given this, have decided to take
some of the counties in far northern Iowa out of the Flood Watch,
but, given the variability in the QPF axis, have remained
conservative with adjustments. Therefore, the Flood Watch remains in
effect for Highway 3 and Highway 20 counties and south through
Thursday. For more information on flooding concerns, please
reference the hydrology discussion below.

While heavy rainfall is the primary concern today, the storm
prediction center (SPC) has pulled the marginal risk for severe
weather (level 1 of 5) slightly farther north now nudging right up
to our far southwest CWA. A pocket of higher instability (~1000
J/kg) does develop just to our southwest ahead of the low pressure
this afternoon and evening, which combined with favorable wind
fields and an assumption of surface destabilization, could result in
a few supercells. The warm cloud layer likely won`t support much
hail production, but gusty winds and even a tornado could occur with
these storms. Fortunately for those in Iowa, we generally don`t see
the clearing that may take place to our southwest, keeping profiles
saturated with very poor low to mid-level lapse rates. Likewise, the
time the warm sector arrives in Iowa will be favoring a decreasing
severe thunderstorm potential. Therefore, it seems unlikely that any
severe weather makes its way into our area, but it will be something
worth monitoring should any stronger storms linger into far
southwestern Iowa.

Rainfall continues into early Thursday morning, but slowly pushes
south and eastward as the front sags through mid-day. Rain will
activity will linger along the front along far southeastern Iowa
into Thursday afternoon, but the heaviest amounts will have already
pushed out of our area. Rain looks to completely depart by around
00z Friday (Thursday evening), giving way to drier conditions
overnight.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Issued at 306 PM CDT Tue Sep 29 2026

The extended forecast begins with decreasing coverage of showers and
thunderstorms as a cold front pushes the slow-moving surface low out
of the region, bringing an end to the prolonged period of heavy
rainfall that has affected the area since Tuesday. Behind the front,
cold air advection will support cooler, much more autumn-like
temperatures starting Friday and persisting through much of the
extended period. In addition to the cooler temperatures, surface
high pressure will build across the region, keeping conditions
predominantly dry. However, long-term deterministic models indicate
a minor shortwave passing through the area Saturday night into
Sunday, though measurable precipitation associated with this feature
will likely be confined to northern portions of the CWA. Otherwise,
surface high pressure rapidly reestablishes itself, ensuring a
continued period of seasonable autumn weather across the region.

A passing cold front will clear the slow-moving surface low out of
the region, putting an end to the persistent heavy rainfall seen
since Tuesday. High pressure and post-frontal cold air advection
will bring cooler, dry, autumn-like conditions from Friday through
the extended forecast period, with only a minor shortwave bringing a
brief chance of precipitation to northern portions of the area over
the weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1150 PM CDT Tue Sep 29 2026

Showers are gradually decreasing in coverage across Iowa tonight,
though KOTM/KDSM may not see a long break before more showers build
in mid day. CIG lowerings and fog is off to an early start in
central and southwest Iowa. IFR/LIFR thresholds may be reached at
various points tonight as this area expands to all the terminals,
especially from 11z-13z. A prolonged and high confidence period of
showers builds south to north tomorrow, likely affecting all except
KMCW. Some chance for thunder exists towards the end of the period,
though confidence is too low for inclusion in this issuance.

&&

.HYDROLOGY...
Issued at 306 PM CDT Tue Sep 29 2026

Potentially significant hydrologic event will affect our CWA over
the next several days, with flash flooding, areal flooding and river
flooding possible. Shifts in locations and amounts of heaviest
rainfall may significantly affect stream responses especially creeks
and smaller streams.

Greatest threat of heaviest rainfall is presently across the
southeast two-thirds of CWA per latest meteorological model trends,
however possible later wobbles to the north may bring our northwest
counties into play again, thus we have continued the flood watch in
those areas. Elsewhere, the river basins of most concern presently
include the middle/lower Raccoon basin, Des Moines River basin below
Saylorville Reservoir including tributaries like the North, Middle
and South Rivers, and the South Skunk River basin especially
downstream of the Ames area. Of those three, the Raccoon is of most
concern due to recent moderate to heavy rain across portions of that
basin, leading to increased soil moisture, which will allow more
runoff to occur more quickly.

Latest Hydrologic Ensemble Forecast System (HEFS) and QPF ensemble
hydrographs, which include longer QPF time durations than our
deterministic river forecasts, suggest the most likely scenario in
many locations will significant within-bank rises to around
bankfull, with some isolated minor river flooding. One outlier is
the lower Raccoon basin where some moderate flooding is possible. If
rainfall amounts overachieve then more widespread minor to moderate
river flooding would be possible. Although unlikely, higher end
rainfall amounts would lead to more widespread moderate to major
river flooding. Refer to our HEFS or QPF ensemble hydrograph
forecasts for more details.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through late Thursday night for IAZ024>028-033>039-
044>050-057>062-070>075-081>086-092>097.

&&

$$

SHORT TERM...Dodson
LONG TERM...Vorst
AVIATION...De Bruin
HYDROLOGY...Zogg