203
FXUS63 KDMX 030617
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
117 AM CDT Thu Sep 3 2026

.KEY MESSAGES...

- Heat and humidity will persist through Friday and perhaps
  beyond. The Heat Advisory remains in effect for areas along
  and south of Interstate 80.

- Scattered thunderstorms will affect portions of western and
  northern Iowa through this morning, but severe weather is
  unlikely. Low thunderstorm chances (~30%) are then forecast in
  far northeastern Iowa late tonight into Friday morning, where
  there will be a marginal risk of severe storms.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 117 AM CDT Thu Sep 3 2026

A large heat dome remains entrenched across the southeastern
and central U.S., with a deep-layer ridge extending northwest
from it that will steadily build over the Midwest and Iowa
through the end of the week. This will support a continuation of
the hot and humid conditions we have seen for much of the week
already, and little change has been made to the temperature and
humidity forecast, nor has any change been made to the ongoing
Heat Advisory in our central and southern counties that runs
through Friday evening. The only fly in the ointment regarding
heat persistence would be convective/precipitation impacts, but
those appear generally less likely the next couple of days, at
least during peak heating times.

At the surface, a large ridge lies to our southeast beneath the
aforementioned heat dome, while a broad low pressure trough
remains in the lee of the Colorado Rockies. A largely washed out
surface trough/boundary extends from that area up into the
Midwest, and currently appears to lie across far northern and
northwestern Iowa. Meanwhile, the nocturnal low-level jet has
once again developed/intensified since last evening, but tonight
is oriented more over eastern Nebraska and pointing into the
Iowa/Minnesota/South Dakota tri-state region. Scattered
thunderstorms have developed in northwestern Iowa over the last
few hours, as a result of the strengthening low-level jet
overlying the nebulous surface boundary. As the jet pivots
slightly northeastward early this morning, it will lead to an
expansion of showers and storms across our northern and western
counties, though instantaneous coverage should remain isolated
to scattered and thus POPs are capped around 50% in that area.
Without upper-level support for ascent and with effective bulk
shear fairly weak and steadily weakening further, severe weather
is unlikely. The showers and storms will then gradually fade out
this morning after sunrise as the jet diminishes and the warm
layer aloft reasserts itself.

A 500 MB trough will move east northeastward across the Dakotas
today, overtopping the ridge and then turning more southeastward
late tonight. It is likely that an MCS will develop in the
regions to our north around this evening, then track
southeastward across Wisconsin and surrounding areas as a
result. There is a possibility these storms could scrape our far
northeastern counties late tonight/Friday morning, however,
with the synoptic ridge building overhead it is more likely they
will remain farther northeast toward Wisconsin, and most model
guidance has trended in that direction as well. The SPC
Convective Outlook reflects this trend, with a Marginal Risk
coming down to around Mason City and Waterloo, but the higher
risk categories shifting into Minnesota/Wisconsin/Lake Michigan.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 243 PM CDT Wed Sep 2 2026

Nocturnal and morning convection, mainly across northern Iowa, is
expected to continue each day through at least Sunday morning. With
only modest forcing severe chances each day are fairly low. The next
more organized convection chance is not until early next week and
that will help to squash the ridge and bring at least some relief to
temperatures for a few days. Until then, heat continues this weekend
with heat indicies in the upper 90s to low 100s across southern and
into central Iowa. With the holiday weekend coming up it is
important to remember heat safety for any outdoor plans that are in
place. Minimize time outside, hydrate, and take breaks in the shade.
By late week the thermal ridge looks to rebuild with heat and
humidity lifting back north into the area, along with continued
scattered storm chances.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1151 PM CDT Wed Sep 2 2026

The expectation remains for showers and storms to develop
further across northern Iowa through the morning hours, but
should remain VFR. Exact timing and coverage details may need to
be adjusted slightly based on trends over the next several
hours. Otherwise, widespread LLWS is expected through the
morning for all sites but KOTM, before decreasing after 14-16z.
Drying conditions are then expected across the terminals beyond
16z, with winds out of the south/southwest increasing up to
15-20 knots.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...

Heat Advisory until 7 PM CDT Friday for IAZ057>062-070>075-
081>086-092>097.

&&

$$

SHORT TERM...Lee
LONG TERM...Hagenhoff
AVIATION...Bury