304
FXUS63 KDMX 180755
AFDDMX

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

.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 /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1058 PM CDT Fri Jul 17 2026

VFR conditions to prevail through the period. Continued to add
FM groups to reflect a wind shift with a passing front tomorrow.
20% chance of showers and thunderstorms mainly for KOTM after
20z. Will be able to add in mentions once the placement of the
front is better known.

&&

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

&&

$$

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