305
FXUS63 KDMX 181943
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
243 PM CDT Sat Jul 18 2026

.KEY MESSAGES...

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

- Scattered thunderstorms across south central to southern Iowa
  this afternoon and evening. The severe potential is low,
  though an isolated severe storm cannot be ruled out in SE Iowa.

- More widespread thunderstorms are expected into Monday
  morning, and again into late Monday afternoon through the
  evening. Strong to severe storms are possible.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 243 PM CDT Sat Jul 18 2026

A look at surface features today shows an area of low pressure over
the northeastern CONUS, while an area of weaker high pressure sits
over the Northern Plains. Over Iowa, a boundary is draped generally
from west to east across central Iowa, near the I-80 corridor, which
did produce weak showers and storms through about mid-morning over
northern to northeastern Iowa before tapering off. Much of
northeastern Iowa received around a quarter to half inch of rain,
with localized three-quarter inch values from this earlier activity.
Thanks to this passing boundary to the north, temperatures so far
are slightly cooler with values in the low to mid 80s, which may
only increase a few more degrees this afternoon yet. Ahead of the
boundary, temperatures are still expected to warm up to similar
values as have been observed the last several days, with highs in
the low to mid 90s. This boundary will also be the focus for the
expected development of showers and thunderstorms into the late
afternoon through the evening. Moisture convergence along the
boundary will aid to lift parcels through a favorable environment
characterized by instability values around 2500-3000 J/kg, though
weak shear values around 10-15 knots and poor lapse rates will
largely be working against storms from becoming strong/severe. There
is a low possibility that a storm could produce a sub-severe and
possible isolated severe gust over southeast Iowa where DCAPE values
over 1000 J/kg are noted. Besides the potential for wind, efficient
rainfall is possible during the extent of storms as they go up and
quickly come down, given PWATS around 2 inches and warm cloud depths
over 15 kts that could lead to rainfall amounts up to an inch or
slightly higher. Outside of localized heavy rainfall with this
activity, flooding is not a concern at this time.

While the aforementioned area of low pressure departs further east
late tonight, the surface high will pass southeast into the Great
Lakes, with the boundary moving into northern Missouri. A gradual
decrease in instability and continued weak flow will lead to the
waning of storm development and the overall return of dry conditions
across the state. Overnight conditions will feature more comfortable
temperatures in the 60s, paired with mostly clear skies. Cannot rule
out localized patchy fog in low lying areas through sunrise. As the
previously mentioned area of high pressure tracks southeast across
the Midwest, the area of subsidence associated with it will cover
the greater majority of Iowa, keeping much of the area dry with
light southeast winds as highs reach into the upper 80s to low 90s,
with similar heat indices given slightly lower dewpoints than
yesterday in the mid to upper 60s. Wildfire smoke that has impacted
areas further north and east of Iowa over the past several days will
make it`s way into portions of eastern Iowa through the day due to
this shift in winds, before decreasing into Monday. However, the
thicker smoke should generally remain east of the forecast area.
Over southwestern Iowa, a lingering boundary and instability axis is
indicated to be overhead, which could result in some development of
isolated showers and storms into the afternoon to early evening
timeframe, though the bulk of activity looks to generally occur over
Missouri.

Into the start of the upcoming work week, a rather potent shortwave
trough over Alberta/Saskatchewan Canada is progged to gradually
shift southeastward across the Upper Midwest through Monday, which
will shove the ridge westward of Iowa and therefore place the
Central Plains into an upper level northwest flow regime. At this
same time, low level west/southwest flow will increase into the
area, resulting in the advection of warmer and more humid air into
Iowa. In the morning, a boundary is expected to pass
east/southeastward across Minnesota and into Wisconsin, where a
decaying MCS is indicated to gradually track. There is a
potential that this system passes through some portion of
northern and northeast portion of Iowa during this period, with
the main concern being damaging wind gusts as storms organize
into a bowing segment, though small hail cannot be ruled out
given the elevated nature of these storms. There is still
uncertainty on the exact track of this system, so will have to
keep an eye on later model runs and adjust per latest trends.
Dry conditions are expected to return later in the morning
through the afternoon, with the push of warmer and more humid
air into Iowa leading to the hottest day in the forecast as
highs are expected to push through the mid to upper 90s and
dewpoints surge into the low to mid 70s across the forecast
area. These conditions will result in widespread heat index
values over 100 degrees, with heat headlines likely issued later
this weekend as confidence continues to grow, so stay tuned.
Those spending time outdoors should take frequent breaks in the
shade and stay hydrated.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Issued at 243 PM CDT Sat Jul 18 2026

As the deepening shortwave arrives into the Upper Midwest into
Monday evening, a cold front is expected to push into northern Iowa
and gradually track southeast over the state. Stronger forcing for
ascent and moisture availability will be present overhead, paired
with aforementioned hot and humid conditions. This environment
will feature high instability values over 4000+ J/kg and strong
shear values over 50 knots, which will be more than favorable to
produce organized convection capable of becoming strong to
severe, where all hazards would be in play. As storms evolve
into late Monday to early Tuesday morning, the development of
another MCS is indicated that looks per model guidance to move
across northern into eastern Iowa, with additional concerns for
potential severe winds and heavy rainfall given very favorable
PWATS around 2+ inches and warm cloud depths around 16 kft. More
specific details will become more clear in the coming days, but
planning for potential severe weather can start now by
monitoring the forecast, having multiple ways to receive
warnings, and altering plans as needed.

Showers and storms are expected to taper off after sunrise Tuesday,
with surface winds shifting northwest as the mid-level trough and
associated deepening low pressure system departs the region. A
tightened pressure gradient on the backside of this system will
bring breezy conditions through the day, with gusts up to 20-30 mph.
Highs as a result will also be ``cooler`` with values in the 80s,
and dewpoints in the upper 50s to low 60s. The pattern through
midweek generally remains the same as the ridge remains west of the
region and upper level northwest flow continues to bring slightly
cooler and less humid conditions overhead, as highs generally top
out in the 80s and dewpoints reach into the upper 50s to low 60s.
Subtle waves riding the larger scale flow with periods of some level
of moisture return though could bring additional chances of showers
and possible storms to Iowa later Wednesday through Friday, though
details are not as clear on exact timing and coverage details of
this activity and will be refined in the coming days. More summer
like conditions are expected to return near the end of the work week
as temperatures gradually return into at least the low 90s as the
ridge strengthens once again.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1238 PM CDT Sat Jul 18 2026

A boundary slowly sinking across Iowa this afternoon has led to
some localized areas of MVFR conditions due to low ceilings at
KFOD and KALO, but should improve over the next few hours, with
a potential for similar conditions to arrive at KDSM and KOTM
after 20-21z or so, but only for a short period. Otherwise,
expecting storms to develop into south central to southern Iowa
late this afternoon to evening, with KOTM possibly impacted and
less confidence further north to KDSM, though trends will be
monitored closely. Winds through the period are expected to
remain light, shifting northeasterly tonight and then
southeasterly towards the end of the period. Cannot completely
rule out localized patchy fog around sunrise. Wildfire smoke
moving into Iowa from the southeasterly flow late in the period
may also bring in slightly reduced visibilities but still VFR
conditions.

&&

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

&&

$$

SHORT TERM...Bury
LONG TERM...Bury
AVIATION...Bury