434
FXUS63 KDMX 181141
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
641 AM CDT Sat Jul 18 2026

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

.KEY MESSAGES...

- Hot and humid through the weekend with heat peaking on Monday.

- Scattered thunderstorms across southern Iowa this afternoon
  and evening. The severe potential is very low.

- More widespread thunderstorms are expected on Monday. Strong
  to severe storms are possible.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 255 AM CDT Sat Jul 18 2026

High pressure centered south of the state has kept skies clear
across most of Iowa through the overnight with very light wind.
Meanwhile, the trough across the Great Lakes region has deepened
with a boundary trailing across Wisconsin and into Minnesota.
Thunderstorms have developed along this boundary overnight and
continue early this morning as it sinks into northern Iowa.
Convection is expected to largely pass east of the area nearer the
better forcing and diminish with sunrise, though an isolated
thunderstorm may clip northeast parts of the area early this
morning. That trailing front will continue to sink across Iowa
through today. Northern Iowa will see the most notable effects, as
the boundary pushes south early enough to impact day time highs.
Temperatures there will top out in the mid 80s. Central and
southern Iowa will be delayed such that temperatures will warm
through the low 90s yet today. With dewpoints in the low 70s
south of the boundary, heat indicies in central to southern
Iowa will near 100 this afternoon. The boundary reaches southern
Iowa late afternoon into the evening. Thunderstorms are
expected to redevelop along the front which will likely be along
and south of the I-80 corridor. There will be 1500+ J/kg of
MLCAPE available for storm development, but very little (<15
kts) effective shear to organize convection. As such, storms are
expected to be short lived and sub-severe.

On Sunday the thermal ridge rebuilds and shoves the boundary off to
the north and east with temperatures into the low 90s again for much
of the area. Isolated thunderstorms are possible in the
afternoon along this remnant boundary, however forcing is quite
weak and any development is expected to be rather isolated in
nature should it occur. Zooming out, a shortwaves moving across
Canada will reach the upper midwest and the Great Lakes trough
late Sunday. This interaction will result in a couple local
impacts. First, the trajectory of upper level flow will shift
such that smoke that was sweeping east may filter into parts of
northern and eastern Iowa on Sunday. This trough will also bring
better forcing to the area with a strong upper level jet now
overhead later Sunday and on Monday. With the troughing north
and east and thermal ridge to the west, a notable gradient in
instability looks to set up across Iowa along which storms are
expected to develop and follow on Monday. With better shear (40+
kts at 0-6 km) for storm organization and more than sufficient
instability (2000-2500+ J/kg MLCAPE), severe storms are
possible.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 225 PM CDT Fri Jul 17 2026

The long-term forecast has much more uncertainty. For Monday,
deterministic models are hinting at more thunderstorm potential with
our biggest consideration being the location of the ridge. The
eastern extent of the ridge`s influence will determine the axis
of where any organized convection would track. The most notable
takeaways as far as storm potential Monday is that the
ingredients are in place and better forcing will be available as
we have a pattern change taking place. As we transition to
northwesterly flow, subtle shortwaves will ripple overhead which
will drive any precipitation chances through the next week.
LREF and deterministic guidance show that the ridge will be well
clear of Iowa through midweek, which would lead to an increased
area of potential coverage for showers and thunderstorms as
opportunities arise. Finally, with this pattern chance,
temperatures are going to trend cooler. Instead of making daily
runs for the 90s, temperatures will be in the lower to mid 80s
at points through the week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 641 AM CDT Sat Jul 18 2026

A few scattered thunderstorms have developed near KMCW that will
be south of the terminal by 12z. A front will sink south across
Iowa today with winds shifting to out of the north behind it,
then northeast by this evening. Scattered thunderstorms will
redevelop on the front in central and southern Iowa this
afternoon and evening. Have included prob30 mention of -TSRA at
KOTM where impacts are most likely. A stray storm may reach
near KDSM, however confidence is lower here and have not
included in the TAF at this time.

&&

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

&&

$$

SHORT TERM...Hagenhoff
LONG TERM...67
AVIATION...Hagenhoff