443
FXUS63 KDMX 142055
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
355 PM CDT Mon Sep 14 2026

.KEY MESSAGES...

- Severe thunderstorms late this afternoon into this evening
  with large hail, damaging wind gust, and a few tornadoes
  possible. Heavy rainfall with the potential for flash flooding
  becomes an increasing concern overnight, particularly in
  cities and towns.

- Heavy rain and storm chances continue through at least the
  middle of the week and possibly the end of the week, leading
  to both flash flooding and river flooding concerns.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 355 PM CDT Mon Sep 14 2026

The main weather theme over the period will be an active, wet
pattern into this next weekend. Of course, there will be intervals
of dry conditions, but rounds of rainfall will lead to increasing
threats of flash flooding over varying parts of the state. All of
the rainfall will also lead to rises on many if not most of our area
waterways. In some places, this may push the rivers above flood
stage. In addition, there is the risk of severe storms late this
afternoon into this evening before the event transitions to heavy
rainfall and flash flooding potential.

At present, the warm air advection wing of showers and thunderstorms
has lifted northeastward through much of central Iowa early this
afternoon. One of the forecast questions in previous days has been
the amount of clearing and potential destabilization. GOES-East
visible satellite imagery shows clearing in southwestern Iowa, which
should migrate into central Iowa. To the north over northern Iowa,
cloud cover may linger along with showers and this may create a
differential heating boundary in addition to the synoptic cold front
that will move in late today into tonight. Forecast soundings show
low level warm layer capping, which is expected to inhibit any
surface based storms. However, if storms are able to develop and
overcome this inhibition through daytime boundary layer mixing, a
few tornadoes would be possible given the strong kinematic
environment. If surface based storms do not form, elevated storms
are likely with strong MUCAPE values and mid-level lapse rates
around 6C/km. As alluded to, there is no lack of kinematic forcing
and shear with the right entrance region of a jet streak over the
region. The storms being elevated does take some edge off of the
impressive deep layer shear and storm relative helicity (SRH)
values; however, the bulk shear and SRH values are still very
favorable for severe storms, including elevated supercells, at least
initially, until they merge into a line of storms. These storms
would pose a risk of damaging wind gusts and hail with the hail risk
waning as the storms merge into a line. As this occurs, the 0-3km
shear values over 30 knots are in place to support a mesovortex
potential, especially if a line of storms can orient itself north to
south and thus more orthogonal to the shear vector. This remains to
be seen whether anything to the surface could materialize.

While the severe risk will wane by late evening, the heavy rainfall
and flash flooding potential will be going up through the evening.
There will be strong moisture transport into the region on the nose
of the low level jet upwards of 50 knots. This will bring
precipitable water values (PWATS) up to around 2 inches with warm
cloud depths topping 4000m - both unusually high for mid-September.
The 850-300mb around 40 knots, this is a bit fast, but it is
oriented fairly parallel to the boundary, which would result in
repeat rounds of rain (aka training storms). Deterministic has 2 to
4 inches with ensemble localized probability matched mean
(LPMM) from the HREF and REFS of 3 to 5 inches with localized
bullseye amounts of 7" in southwest to northeast oriented swaths
from somewhere in southwest Iowa into central Iowa. These are
areas that saw significant rainfall middle of last week with
additional rainfall across much of the area today. NASA SPoRT
soil moisture percentiles show reduced capacity in those areas
and a heightened risk of flash flood potential. Thus, the flash
flood watch continues to look well placed for tonight into
Tuesday morning with a slight expansion on the eastern side,
which will be discussed more below.

The surface boundary is forecast to slip south of the state by
midday Tuesday, but this does not mean the end of heavy rainfall,
just a change in location. The elevated 850mb boundary never leaves
the state and is forecast to lift back northward Tuesday night into
Wednesday. So, while the highest PWATs may be pushed to around the
Missouri border Tuesday night, they will move back northward,
especially into the day Wednesday. Thus, the risk of heavy rainfall
and flash flooding potential in play is highest from roughly I-80
southward through Tuesday night into Wednesday morning. With the
risk for another round of heavy rainfall, have extended the flash
flood watch through through midday Wednesday. There may be some
adjustment in area, but for now have kept the watch as simple as
possible. There does remain uncertainty in the amount of coverage of
rain and storms on Wednesday, but the environment that will be in
place will be favorable for heavy rainfall.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Issued at 209 PM CDT Mon Sep 14 2026

On a broad scale, Iowa will reside in generally fast flow around mid-
level high pressure over the Deep South/Southeastern US, which will
migrate slowly back to the west by week`s end. In this fast flow,
there will be a few shortwave troughs that pass through along with
fragmented vorticity pieces, which will interface with a surface and
elevated boundary draped across the region if not the state at
times. The pattern is thus conducive to additional rounds of
rainfall on what will be increasingly saturated soil and thus
increased risk of flash flooding with each successive round of rain.
This rainfall will route into waterways and lead to increasing river
levels with additional details in the hydrology discussion
below.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1255 PM CDT Mon Sep 14 2026

Aviation concerns in this period are multi-fold with storm
timing and impacts as well as low level wind shear. Showers and
storms are moving to the northeast from FOD to GGI and will
continue to lift in that fashion with brief bouts of IFR/MVFR
restrictions possible as these pass over MCW/ALO in the next few
hours. MVFR ceilings over northern Iowa are forecast to largely
miss terminals so VFR conditions are expected after the storms
this afternoon. However, additional storms are forecast into
tonight sliding southeastward with time, but lingering the
longest at DSM and OTM. Low level winds will also increase and
create a period of wind shear. Precipitation will end over
northern Iowa (e.g. FOD/MCW) by daybreak Tuesday and likely ALO
by midday Tuesday.

&&

.HYDROLOGY...
Issued at 210 PM CDT Mon Sep 14 2026

Flash flood and river flood concerns continue this week due to
forecast multiple rounds of moderate to heavy rain. Flash flooding
is more of a concern in the short term (later today into Tue
morning). Short term National Water Model rapid onset flooding (ROF)
guidance continues suggesting the greatest risk of flash flooding
mainly between US Hwy 30 and the MO border, or roughly the same area
included in the current flood watch. Most likely scenario will be
ponding and low end flash flooding, however if QPF overachieves then
pockets of more significant flash flooding may occur especially over
urban areas. Since general storm motion is anticipated to be from W-
E or SW-NE, small stream basins oriented in those directions would
be most susceptible to flash flood impacts especially with training
thunderstorm activity. Additional heavy rain will prolong flash
flood concerns beyond Tue morning.

Longer term, river flood concerns exist too. The NBM-forced National
Water Model (NWM) with 10 days of QPF shows significant within-bank
rises on many streams across roughly the southeast half of the CWA,
with some minor flooding possible. The GEFS-driven Hydrologic
Ensemble Forecasting Service (HEFS) basically agrees, with 50%
exceedance probabilities showing several streams reaching action
stage or minor flood stage in central IA. The 30% exceedance
probabilities show more pervasive minor flooding with a few
locations at moderate flooding. The 10% level shows moderate to
major river flooding across much of the southeast half of the CWA.
Variations in QPF location and amounts as well as mesoscale features
after each successive round will greatly dictate what happens, but
the river flooding component is worth monitoring closely.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Wednesday afternoon for IAZ025>028-034>039-
045>050-057>062-070>074-081>084-092>095.

&&

$$

SHORT TERM...Ansorge
LONG TERM...Ansorge
AVIATION...Ansorge
HYDROLOGY...Zogg