533
FXUS63 KDMX 121957
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
257 PM CDT Sat Sep 12 2026

.KEY MESSAGES...

- Scattered to widespread shower and storm chances increasing
  early Sunday. Locally heavy rainfall amounts may lead to
  ponding water or minor flash flooding.

- Heavy rain and thunderstorms possible Monday. Some may be
  severe, especially in the afternoon. Heavy rainfall and
  training storms may result in flash flooding.

- Heavy rain and storm chances persist through at least mid-
  week. River flooding and flash flooding is possible.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 254 PM CDT Sat Sep 12 2026

>> MILD TODAY WITH OCCASIONAL RAIN SOUTH

Mostly clear skies and light to breezy winds are prevalent over much
of Iowa today, as the surface front this morning has now completely
pushed through the area. While many are enjoying the mild September
weather, there are a small few in southern Iowa currently
experiencing isolated showers and light rain over southern Iowa.
This activity is riding the back edge of the moisture and
instability gradient. The moisture gradient generally stalls out
along the Iowa/Missouri border this afternoon and evening which will
keep at least low end rain chances over northern Missouri and
southern Iowa. None of this activity is expected to be severe, but
occasional lightning is possible.


>> INCREASING SHOWER AND STORM CHANCES LATE TONIGHT THROUGH
SUNDAY

An 850 mb low level jet (LLJ) will begin to ramp up this evening
over the Oklahoma and Texas panhandles, nosing up into Kansas
and northwestern Missouri. While the strongest part of this LLJ
won`t quite reach up into Iowa, it will be advecting warmer,
moist air up into Iowa tonight into Sunday morning. At the same
time, a broad trough will be passing through the upper level
flow pattern and reinforcing the high pressure over Iowa. The
interaction of these two features will produce modest low- to
mid-level lift as the warm, moist air mass to the south
converges with the cooler, drier air mass over Iowa. The net
result will be scattered to potentially widespread shower and
storm chances starting early Sunday morning and lasting through
at least mid-day.

The HRRR, NAM and RAP are certainly the most bullish solutions with
this Sunday activity, as they have the southerly 850 mb flow pushing
farther up into the state. These solutions are also keying on a
frontogenetical zone setting up over southwestern into central Iowa
through the morning. Storm motions will generally be parallel to
this convergence zone, leading to training showers or storms through
the morning. PWATs in these solutions will be above the 90th
percentile for this time of year, generally around 1.6" to 1.7",
suggesting healthy rainfall. Combine this with weak instability
aloft and we could be looking at rainfall amounts around 2" or
higher within this focused area of ascent. Should these amounts over-
perform, or fall over more urban areas, we could see some ponding or
minor flash flooding issues on Sunday. It is worth noting that these
are just a few solutions. The rest of the model suite seems less
convinced by the northern extent of the 850 jet and moisture,
keeping the heavier amounts to the south and west of the area.
Outside of the heavy rain threat, the potential for severe weather
appears fairly low given the elevated storms and skinny CAPE
profile.


&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 254 PM CDT Sat Sep 12 2026

>> HEAVY RAIN AND THUNDERSTORM POTENTIAL MONDAY MORNING

The active pattern continues into at least the first half of the
work week, starting with Monday. The trough developing over the
pacific northwest will begin to push eastward toward Iowa Sunday
night into Monday, briefly pushing upper level ridging through
Sunday afternoon. However, this ridging will be short-lived as
return flow begins to advect warm, moist air up into the state
behind the 500 mb ridge and ahead of the trough. The warm air
advection wing will first arrive in Iowa on Monday morning, pushing
north and eastward through mid-day. Some isolated pockets of heavy
rainfall are possible with this early day activity, but should
progressive enough to negate flooding concerns. The severe risk also
looks fairly isolated, as instability will be meager (~500 J/kg) and
elevated. However, a 45 to 55 kt 850 mb jet will accompany the theta-
e push, bringing some gusty wind potential both with or without
storms. NBM winds are generally max out around 40 mph, but could
very well overachieve that and approach wind advisory criteria.


>> SEVERE THUNDERSTORM AND FLASH FLOOD POTENTIAL MONDAY
AFTERNOON

By Monday afternoon, better instability (~1500 J/kg) will begin to
develop in the warm sector along with 50+ kts of deep layer shear.
The limiting factor will be warm low- to mid-level temperatures
leading to a notable amount of convective inhibition. Therefore, any
thunderstorms that occur will need to overcome this cap, which will
be most likely along the southwest to northeast oriented boundary
from western into northern Iowa. This boundary is expected to be the
focal point for thunderstorm activity through the afternoon and
overnight into Tuesday. Monday afternoon, some strong to severe
storms will certainly be possible along the boundary, with hail and
wind being the primary concerns. A tornado threat does exist as
well, thanks to a healthy amount of low level turning, but would be
contingent on storms becoming rooted at the surface. This
conditional risk has prompted the storm prediction center to issue a
Day 3 slight risk focused on western into central Iowa for Monday
afternoon.

Along this boundary will also be a quite moist environment with
PWATs pushing 2" or higher, which would put them at the high end of
climatological PWATs for this time of year, suggesting efficient
rainfall production. Likewise, storm motions parallel to the
boundary will lead to training storms and a heavy rain and flash
flooding threat Monday afternoon through the overnight. The highest
amounts are currently being modeled over northern Iowa, with 24 hour
QPF amounts of 3 to 5" being depicted by 18z Tuesday. The location
of course will be dependent on where the boundary sets up, so it`s
likely this area will shift through the coming days. However, the
signal is certainly there for a heavy rain threat Monday night
through Tuesday. Should these amounts be realized, flash flooding is
possible if not likely, especially if it occurs in any urban areas.
The weather prediction center rightfully has slight risks for
excessive rainfall over Iowa every day starting tomorrow through
Wednesday.


>> FLOODING CONCERNS INTO THE MIDDLE OF NEXT WEEK

The aforementioned surface boundary continues to produce storms
Tuesday into Wednesday as well. Breaks will likely occur between
pockets of forcing, but heavy rain and storms persist each day
through Wednesday and potentially beyond. The weather prediction
center rightfully has slight risks for excessive rainfall over
Iowa every day starting tomorrow through Wednesday. In addition
to the flash flooding concerns, we may see rivers beginning to
respond as well. GEFS-induced hydrologic ensemble forecasts
suggest many of the rivers over north central into southern and
eastern Iowa could be pushing into action or flood stage by the
second half of next week. Unfortunately, the active pattern
really doesn`t look to let up through the second half of the
work week and into next weekend, but solutions diverge at that
point.


&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1219 PM CDT Sat Sep 12 2026

VFR conditions prevail over the state today. Breezy north
northwesterly winds with gusts around 15 to 20 kts have
developed behind a front that passed through this morning.
These breezy winds will persist for a few hours this afternoon,
before diminishing into the evening. Light to calm winds are
expected overnight. Rain and thunderstorm chances return to the
area Sunday morning, primarily impacting KDSM and KOTM, although
any terminal could see a shower through the morning. Confidence
is lower in the widespread nature of showers, so have only
included precipitation mention in TAFs where confidence is best
(ie KDSM and KOTM). Occasional thunder is also possible with
this activity, but have opted to leave out of TAFs at this lead
time.

&&

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

&&

$$

SHORT TERM...Dodson
LONG TERM...Dodson
AVIATION...Dodson