975
FXUS63 KDMX 301937
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
237 PM CDT Sun Aug 30 2026

.KEY MESSAGES...

- Increasing late season heat and humidity into this upcoming
  week, especially over southern Iowa where heat index values
  will be around 100 degrees at times. A Heat Advisory has been
  issued for portions of southern Iowa Monday afternoon through
  Wednesday afternoon.

- Storm chances highest over parts of central into northern Iowa
  with the most likely timing overnight into the early morning
  hours each day through at least Thursday morning.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 237 PM CDT Sun Aug 30 2026

Weak, low level thermal lift and strong kinematic forcing aided
in scattered thunderstorms moving over a good portions of Iowa
this morning with the back edge pushing into eastern Iowa this
afternoon. This activity is on the northern periphery of the
mid-level ridge, which will be slowly drifting and lifting
northeastward early this week. Meanwhile, broad troughing will
remain over the western US keeping the track of shortwave energy
flowing between the two, which is roughly over northern Iowa.
For today, the clouds will continue to move off to the east this
afternoon and temperatures will rise into the low 90s in
southwestern Iowa to the 80s in northeastern Iowa, though
perhaps a degree or two lower than earlier forecast. The
increasing ridge influence will also increase heights and
capping. The different PBL schemes of the convective allowing
models (CAMs) may be in part why the models have showed varied
solutions for the activity this afternoon with different ideas
of the amount of capping. However, a common theme in the CAMs,
which aligns with the conceptual model of capping, is
diminishing coverage and storm potential as any new development
struggles, such as the showers trying to enter western Iowa. The
general trend towards drier conditions is expected to continue
into this evening as the low level jet increases upwards of 45
knots over the state with its nose into northern Wisconsin.
Similar to this morning, the CAMs try to bring scattered storms
into the area from their inception in Kansas/southern Nebraska
towards sunrise and have maintained some low PoPs around this
time into the morning hours Monday after which time they should
dissipate due to weakening low level kinematics and the capping.

While the meteorological calendar will be turning to autumn on
Tuesday, a period of late summer heat and humidity will prevail
Monday through Wednesday over southern Iowa. A surface boundary will
bifurcate the region if not the state in some west to east fashion
through at least the middle of the week. This boundary will be the
focus for possible storm chances, though these will be limited in
the daytime due to the warm low level capping. Thus, storm chances
along and north of this boundary will be highest generally later at
night into the early morning hours both Monday night/early Tuesday
and Tuesday night/early Wednesday. There is a low risk for
elevated strong to severe storms given the modest MUCAPE and low
level jet contributing to higher deep shear values. The boundary
and whatever associated storm activity/cloud cover will also
keep conditions not quite as warm over northern Iowa. South of
this boundary, very warm and humid conditions for early
September will largely prevail into at least the middle of this
upcoming week. Similar to previous forecast shifts, have
continued to shave a few degrees off the initial National Blend
of Models (NBM) guidance for high temperatures, which are at the
upper statistical end of guidance. Part of this is due to
overmixing, such as the GFS which shows highs well into the 90s
to even around 105 degrees, but with dewpoints dropping into the
50s and even 40s at times. That isn`t going to happen to that
degree. Still, temperatures this high will be nearing, though
are currently below, record values by a few degrees. What is
more noteworthy considering this late season heat is the warm
overnight lows, which may challenge record values, in the upper
70s offering little relief from the heat. Experimental HeatRisk
continues to show a large portion of southern Iowa in the
extreme (level 4 of max of 4) category, keying in on the warm
overnight lows and late seasonality of this event. Given the
expected duration and the warm overnight lows despite sub-
advisory heat index values, have issued a Heat Advisory from
Monday afternoon through late Wednesday afternoon for a good
portion of south central into part of central Iowa, including
the Des Moines metro. It should be acknowledged there is
potential for conditions to fail on the northern edge of this
advisory due to potential convective contamination effects of
storms or clouds, but this will be evaluated in the coming days
along with any possible extension later in the week.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
Issued at 237 PM CDT Sun Aug 30 2026

The pattern doesn`t change appreciably late this week with the
center of the ridge over the Tennessee Valley, trough over the
western US, and Iowa on the periphery of the shortwave track.
This will keep the warmest conditions over southern Iowa with
storm chances highest late at night diminishing in the morning
hours over northern Iowa. Into next weekend, there is a signal
the ridge axis amplifies over the Plains, which pushes storm
chances north away from the state.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1211 PM CDT Sun Aug 30 2026

While VFR conditions will prevail much of this period, there
are several items to note. Showers and a few storms are moving
off to the east with their back edge at midday from FOD to OTM.
These will be clear of the terminals by early this afternoon and
bring an end to any brief, low probability MVFR restrictions.
While low chances remain for spotty showers or storms this
afternoon and then again into the day Monday, they are too low
and too uncertain in location to include any mentions.
Otherwise, low level winds will once again increase producing a
period of low level wind shear overnight, which fades from
northwest to southeast from late tonight into the first few
hours of daylight Monday.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 1 PM Monday to 7 PM CDT Wednesday for
IAZ059>062-072>075-082>086-093>097.

&&

$$

SHORT TERM...Ansorge
LONG TERM...Ansorge
AVIATION...Ansorge