674
FXUS63 KDMX 162307
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
607 PM CDT Sun Aug 16 2026

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- A few small showers in southern Iowa this afternoon, then
  clearing by tonight with quiet weather into Monday.

- Thunderstorm chances return at intervals from late Monday
  into Tuesday night. Severe weather may be possible in
  northwestern Iowa around Monday evening into early Monday
  night, then across much of the state on Tuesday.

- A generally active weather pattern continues with lingering
  rain chances from Tuesday night into Thursday or Friday, but
  diminishing severe weather chances during that time.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 102 PM CDT Sun Aug 16 2026

A remnant mesoscale convective forecast has drifted slowly
eastward near the Missouri/Iowa border today, spreading
stratiform rain and isolated thunderstorms across our southern
counties through the morning. Most of the rain has now departed,
but a few patches of sprinkles and a couple of small showers are
lingering this afternoon. These will continue to diminish and
end before sunset. Meanwhile, a large surface high pressure area
is approaching from the northwest and helping to push/erode
thick cloud cover slowly southward, through farther north it is
filling in somewhat with diurnally generated cumuliform. The
high pressure area will settle across Iowa overnight into early
MOnday, providing a brief respite from recent active weather and
helping skies to clear further overnight. It will also bring
lower dewpoints in the upper 50s to mid-60s, but these will be
unfortunately short-lived late tonight into early Monday before
rebounding again as modest southwesterly surface flow returns.
In the interim, very light/calm winds around sunrise Monday with
clearing skies may lead to some potential fog development,
though this is somewhat tempered by the lower dewpoints working
into the area. Some high-resolution models do indicate patchy
fog while others do not, and for now have limited mention in the
official forecast to patchy fog in our southwestern areas near
the Nish valley, but observational trends will need to be
monitored overnight.

A subtle upper level shortwave will move east southeastward
over the Dakotas on Monday, with a reflective surface front
stretching from around western Nebraska into central Minnesota
by Monday evening. With moisture pooling ahead of this boundary
SBCAPE of around 1500-2500 J/KG or so will spread across areas
just to our northwest, and at peak heating the forcing
associated with the approaching shortwave should kick off
thunderstorm development in those areas. Deep- layer shear of
40+ KT is forecast and supercells and severe weather will be
possible over eastern South Dakota, southwestern Minnesota, and
adjacent areas. The frontal boundary will then push into at
least parts of our forecast area Monday night, but with the
upper level wave pushing eastward toward the Great Lakes and
stranding the slowing surface boundary behind, storms should
gradually weaken in intensity as they spread into our area, with
upper forcing and near-surface instability waning. Mid- level
lapse rates also appear less impressive with southeastward
extent, supporting a weakening trend. Still, there is some
threat of at least isolated severe storms mainly in our
northwestern counties around Monday evening, as appropriately
outlined by SPC outlooks.

The old frontal boundary that sags in Monday night will likely
stall out somewhere across Iowa on Tuesday, as a more robust
mid/upper shortwave trough approaches from the west northwest.
Stronger destabilization is anticipated ahead of this wave, with
SBCAPE of 2000-3000 J/KG developing across much of our area by
early to mid- afternoon. Concurrently, 0-6 KM Bulk Shear of
around 40-50 KT will overspread the region from the west, with
hodographs showing weak curvature and relatively straight
orientation. While this presents a favorable synoptic set-up for
severe weather potential, questions remain regarding convective
evolution. Some model solutions depict lingering cloud cover
from decaying Monday night storms that could limit
insolation/destabilization Tuesday morning. Other solutions,
such as the 12Z NAM, develop additional storms in eastern
Nebraska late Monday night and drift them eastward across Iowa
Tuesday morning, likewise limiting destabilization ahead of
other storms that develop later in the day. In any event, high
(70-90%) POPs are maintained on Tuesday, and severe thunderstorm
potential will continue to be assessed over the next couple of
days. There is also the potential for locally heavy rainfall,
particularly in areas that may experience multiple rounds of
storms between Monday night and late Tuesday. Once the main
push of the second shortwave moves overhead around Tuesday
afternoon into the evening, showers/storms should gradually
diminish and trend a bit more southward Tuesday night.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Issued at 1249 PM CDT Sun Aug 16 2026

From Wednesday through Friday, Iowa will continue to reside
beneath northwesterly 500 MB steering flow, though which at
least two more shortwave impulses will travel overhead. At the
surface, however, the old decayed frontal zone should be pushed
to our south over Missouri by convective outflows from
Tuesday/Tuesday night storms. Additional showers may linger in
our southern counties Wednesday into Wednesday night, but then
decrease from Thursday onward with generally 10-30% POPs in the
extended. The quick passage of a surface ridge along with light
northwesterly flow should also allow for somewhat cooler
weather, with daily highs generally in the 70s to lower 80s,
though dewpoints will likely remain in the 60s to lower 70s.
There are some indications that next weekend a larger surface
high pressure system will build into the Upper Midwest and
Great Lakes region, which if this occurs, may provide more
tangible relief from the humidity that has persisted for the
past few weeks.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 607 PM CDT Sun Aug 16 2026

VFR conditions are forecast to prevail through the period at the
terminals. There continues to be a low chance around 30% or less
of MVFR visibility restrictions due to patchy fog toward
sunrise Monday. Given these low probabilities, have continued
to not advertise in the official forecast and will reassess at
6z. Some diurnal cumulus are possible Monday afternoon at least
over eastern Iowa.

&&

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

&&

$$

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