564
FXUS63 KDMX 311129
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
629 AM CDT Mon Aug 31 2026

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

.KEY MESSAGES...

- Increasing late season heat and humidity this week, especially
  over southern Iowa the next few days where heat index values
  will peak around 100 degrees in the afternoons and evenings. A
  Heat Advisory remains in effect for portions of southern Iowa
  from this afternoon through Wednesday afternoon.

- Thunderstorms will be possible at times for the next several
  days, but generally coverage and frequency will be low. Only
  20% chances are carried at times through Tuesday, with a
  higher chance across northern Iowa Tuesday night. There is
  some potential for severe weather, but it is generally
  limited.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 241 AM CDT Mon Aug 31 2026

The forecast for the next few days remains largely unchanged
and characterized by persistent heat and humidity, along with
occasional thunderstorm chances. 500 MB analysis indicates the
large southern U.S. heat dome is currently centered over
Missouri, Arkansas, and Oklahoma. Meanwhile, a low has closed
off over far southern Saskatchewan. Between these two systems,
west southwesterly 500 MB flow is found across the Midwest and
Iowa. This general synoptic pattern will not change appreciably
through Wednesday, except that both the low and the heat dome
will slide slowly eastward, such that by Wednesday afternoon
they will be centered near the Ontario/Quebec border, and
around Kentucky/Tennessee, respectively.

At the surface, a weak low pressure trough has developed along
the High Plains in response to the approaching Saskatchewan 500
MB low. This surface trough currently stretches from around
Western Kansas, up across Nebraska to near the South
Dakota/Minnesota border. A few thunderstorms have developed near
this trough in western Kansas overnight, but have generally
faded as they have attempted to move northeast toward Nebraska
and Iowa. Later today, the trough/wind shift will move eastward
and sag into Iowa, becoming a nebulous stationary front draped
somewhere across our service area. As it does so, there is some
potential for convective initiation to occur in the frontal zone
at times, likely somewhere from our southwestern, through
central, to northeastern counties. A generally moist airmass
will be in place and MUCAPE of 1500-2500 J/KG or so will support
the potential for thunderstorm development. That being said, a
warm layer aloft associated with our proximity to the 500 MB
heat dome will have a suppressing effect, and there is also no
large-scale forcing mechanism to support convective initiation.
The resulting expectation is that a few thunderstorms may
develop during the day, however, coverage will be very low and
any potential for strong or severe storms would be highly
conditional.

Tonight into Tuesday morning, the frontal zone will shift
slowly northward in response to the heat dome to our southeast
reasserting its influence. Once again showers and storms may
develop overnight, however there remains a lack of large-scale
forcing for ascent, and mid-level lapse rates will also become
much less favorable during this time. There are some signs that
the nocturnal low-level jet may redevelop which would aid
initiation, but model depictions of the jet are far less
impressive than on previous nights. Have thus maintained only
slight chance (20%) POPs in a strip near the expected frontal
location overnight, but local adjustments may be needed to POPs
today and tonight based on short-term convective trends if and
when any storms do develop.

After a likely dry day on Tuesday, a 500 MB shortwave trough
will move over the Upper Midwest on Tuesday night and likely
generate clusters of thunderstorms moving roughly from west to
east along the surface frontal zone. By that time mid-level
lapse rates will be steeper and instability will be even higher,
supporting a somewhat larger severe weather potential. However,
it remains to be seen how much these storms would impact
northern Iowa versus Minnesota, as many model solutions have
been trending farther and farther north with the position of the
front.

Aside from generally low chances for thunderstorms and severe
weather, the more widespread weather impact over the next few
days will be oppressive heat and humidity. The onset of the heat
wave was somewhat stunted on Sunday by lingering after-effects
of morning convection. However, more substantial warming is
expected today with the lower rain chances and continuing
airmass modification, and will persist through much of this
week. The primary uncertainty in temperature forecasts revolves
around the position of the stationary front discussed above, and
the nebulous precipitation/thunderstorm chances at times.
Confidence in stifling heat is therefore highest in our southern
counties, which will be more consistently south of the front and
any convective impacts, and also in closer proximity to the heat
dome and associated warm air advection. Have maintained daily
highs in the low to mid-90s in this area for the next several
days, and the Heat Advisory remains in effect to highlight
cumulative heat health effects during this time.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
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 /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 629 AM CDT Mon Aug 31 2026

VFR conditions will prevail through the TAF period. There will
be isolated showers and thunderstorms at times, however, even
within the showers and storms any low ceilings or reduced
visibility will be brief and highly localized. The probability
of such impacts at any terminal at any given time are far too
low for TAF inclusion. If any storms are imminent at a terminal
then an amendment may be considered.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...

Heat Advisory from 1 PM this afternoon to 7 PM CDT Wednesday
for IAZ059>062-072>075-082>086-093>097.

&&

$$

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