330
FXUS63 KDMX 161134
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
634 AM CDT Wed Sep 16 2026

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

.KEY MESSAGES...

- A Flood Watch remains in effect through this afternoon as
  lingering heavy rain threats persist through this morning.

- Many rivers and streams south of Highway 30 and along/north
  of US 34 have seen rises, mostly within bank, but a few
  locations have reached or exceeded minor flood stage.

- Diminishing showers/storms through the day today into this
  evening before coverage of storms increases after midnight
  into Thursday morning.

- Trend towards the heaviest rainfall late this week pushing
  over northern Iowa and north, but saturated soils farther
  south leave conditions susceptible for flash flooding and
  potentially further stream rises.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 340 AM CDT Wed Sep 16 2026

The forecast period begins with the area situated between two main
synoptic features while remaining under the influence of surface
high pressure. Regarding the first feature, yesterdays cold front
has passed through the CWA, but its impacts persist with ongoing
showers and thunderstorms across Missouri and southeastern Iowa. To
our northwest, a second cold front, associated with the persistent
upper-level trough and surface low that pushed yesterdays front
through, is moving southeast from the Northern Plains. Additionally,
a surface wave is noted over the High Plains of western Texas.
Locally, showers and isolated thunderstorms are beginning to lift
northward back into the area from Missouri. While heavy rain is not
anticipated initially, this additional round of rainfall will
maintain moist antecedent conditions ahead of subsequent rounds of
showers and storms.

Through the remainder of the morning and the rest of today, the
stationary boundary will begin lifting north as a warm front,
supported by an upper-level trough moving onshore along the
California coast. This trough will amplify the downstream flow,
leading to upper-level height rises and a gradual decline in PoPs
through the afternoon. However, PoPs will remain around 30 percent
or less through late this evening, primarily over the southeastern
CWA. With decreasing precipitation chances, a temporary reprieve
from heavy rainfall is expected today, allowing the Flood Watch to
expire on time.

This break will be brief, as the aforementioned Texas disturbance
lifts north, driving the warm front across the region late tonight
through Thursday. This system will introduce another round of
potentially heavy rainfall overnight. Forecast soundings ahead of
the boundary exhibit classic heavy rainfall signatures, with
precipitable water and integrated vapor transport values climbing
toward the 99th percentile to maximum of local climatology.
Furthermore, a 25 to 35 knot nocturnal LLJ will advect deep moisture
into the region, serving as a primary focus for convective
development and maintenance. The highest rainfall totals through the
end of the period are currently forecast across Missouri; however,
if the boundary lifts further north or convection over-performs
Wednesday night into Thursday, these higher totals could extend into
areas along and south of the I-80 corridor.

In summary, a short break in precipitation is expected today under
very weak high pressure as yesterdays cold front exits. However, a
disturbance lifting from Texas will drive a warm front into the
region tonight through Thursday, bringing another round of
potentially heavy rain supported by high moisture levels and a
strong low-level jet.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 253 PM CDT Tue Sep 15 2026

Similar to Wednesday, whatever showers and storms early Thursday
look to become less common through the day as forcing weakens.
This will be in part as the ridge over the southeastern US
bulges a bit poleward, which pushes the upper level kinematics
and track of the nebulous vorticity piece away from Iowa.
Further, low pressure over the High Plains look to surge the
elevated warm front well north of the state with the highest
rainfall amounts now trending northward to northern Iowa if not
points farther north over South Dakota and Minnesota. This focus
of rainfall may remain north Friday night into Saturday.
Meanwhile, a substantive trough over the interior West will push
eastward on Friday, which will finally shunt the ridge
southeastward, but also bring the return of favorable heavy
rainfall parameters this weekend. This front should bring drier
conditions at some point, eventually, next week in what is an
overall wet and active pattern until then.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 627 AM CDT Wed Sep 16 2026

Showers are moving across the southern half of the area this
morning with KOTM experiencing light rain but showers are slowly
working northeast toward KDSM. However, showers are beginning to
dissipate; therefore, opted to use a PROB30 at KDSM through
15Z. Otherwise, showers will gradually taper off throughout the
day but KOTM could see lingering showers as a frontal boundary
remains centered over northern Missouri. As the boundary starts
to lift back north, showers and thunderstorms are expected to
move back into KOTM and KDSM after 06Z with PROB30s for KFOD,
KMCW and KALO through the remainder of the period. Along with
increasing rain showers, CIGS and VSBY are forecast to plummet
overnight and widespread categorical IFR to LIFR conditions will
prevail through the remainder of the forecast period. Lastly,
winds will be light and variable.

&&

.HYDROLOGY...
Issued at 253 PM CDT Tue Sep 15 2026

Although flash flood and river flood concerns persist this week, the
overall threat decreased from Monday. In the short term (through
tonight), flash flooding remains a threat mainly along and south of
US Hwy 30, and along and north of US Hwy 34, where top-layer soil
moisture saturation percentages are highest. Additional heavy rain
through tonight may lead to ponding and lower end flash flooding as
far south as the MO border, where amounts and rates may be higher.
At this time, significant flash flooding is not anticipated.

Some rivers and streams have increased significantly from last
night`s rain. These elevated stages and flooding will remain a
concern through at least the end of this week. The NBM-forced
National Water Model (NWM) with 10 days of QPF agrees, suggesting
significant within-bank rises on many streams mainly between US Hwy
30 and US Hwy 34, with some minor flooding possible. The GEFS-driven
Hydrologic Ensemble Forecasting Service (HEFS) basically agrees as
well, however its probabilities decreased from Monday, reflective of
lower trending QPF. The 50% exceedance probabilities show multiple
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 more
pervasive moderate flooding with a few locations at major flooding.
Variations in QPF location and amounts may impact the probabilities,
so people should continue monitoring for river flood potential.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 1 PM CDT this afternoon for IAZ057>062-
070>074-081>084-092>095.

&&

$$

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