804
FXUS63 KDMX 240347
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1047 PM CDT Sun Aug 23 2026

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Generally quiet weather for the upcoming work week, with high
  temperatures in the low to mid-80s each day.

- Some light showers are possible across the western half of
  Iowa late tonight into Monday morning. A few showers and
  thunderstorms will also be possible on Tuesday into Tuesday
  night, with a low risk of severe weather just to our northeast
  in parts of Minnesota and Wisconsin.

- A more active weather pattern will return with additional
  thunderstorm chances next weekend, but any further details
  remain unclear at this range.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 108 PM CDT Sun Aug 23 2026

A large surface high pressure ridge dominates the region today,
stretching from south central Canada down over the Upper Midwest
and Iowa. The result is seasonally comfortable conditions, light
and variable winds, and a lack of low-level clouds. Meanwhile, a
large 500 MB heat dome is sitting over the Desert Southwest and
southern High Plains, with a ridge extending northward into
central Canada. Two relatively subtle shortwave impulses are
overtopping this ridge, with a larger trough moving over the
Washington/British Columbia region. The first of the two
shortwaves is sliding southeastward across Nebraska at this time
and producing light showers there, as well as some higher cirrus
clouds that are streaming over central Iowa but only modestly
blunting insolation. All in all it is a beautiful day for most
outdoor interests in our area.

As the leading impulse slides from Nebraska into Kansas and
Missouri later today, some of the showers over Nebraska may just
clip the southwestern corner of our forecast area. However, dry
air entrainment and subsidence associated with the surface ridge
will inhibit any such eastward expansion, and recent regional
radar trends support the rain staying just to our southwest so
have kept the forecast dry through this evening except for some
20% POPs down by Taylor County. From tonight into Monday, as the
second impulse moves overhead and in closer proximity, gradual
saturation of the atmospheric column should support some light
rain in our western and southwestern counties, mainly after
midnight and into Monday morning. However, even then, there is a
notable lack of instability and forecast soundings still show
fairly substantial dry air to overcome, especially with the
farther eastward one goes in our forecast area. With this in
mind, have maintained relatively low (20-30%) POPs in our
western counties from late tonight into early Monday, but have
lowered them to 10% in our central counties and gone with light
shower/sprinkle wording for the most part. No appreciable
rainfall amounts are anticipated and severe weather is not
expected.

On Monday the surface ridge will begin to drift off to our east,
allowing for a return of light southerly flow. Modest ridging
aloft, in wake of the overnight shortwave impulse, will cause
any lingering showers to fade out by midday and lead to dry
conditions Monday afternoon and evening. By sunset, the
aforementioned larger 500 MB trough currently over
Washington/British Columbia will have progressed to
southeastern Saskatchewan, and will subsequently move east
southeastward to near Lake Superior by Wednesday morning. As it
does so, it will push a reflective surface trough southeastward
through our region, crossing Iowa from late Tuesday through
Tuesday night. Ahead of this surface trough, a period of modest
forcing for ascent ahead of the 500 MB trough, concurrent with
weak warm air/moisture advection in the low levels, supports a
few showers and thunderstorms during the day Tuesday and have
maintained 20% POPs accordingly. Around Tuesday evening,
thunderstorms are expected to develop along the advancing
surface trough closer to the 500 MB low, roughly near the
Minnesota/Wisconsin border. In that region stronger instability
and low-level convergence along the trough supports more robust
updrafts and some severe weather potential, however, this is
more in question heading southward down the trough into Iowa.
The forcing associated with the parent low aloft will be weaker
down here, and the surface boundary a bit more washed out with
weaker low-level convergence. Forecast soundings also hint at
possible capping in the afternoon and evening. As such, have
held POPs low (again, 20%) in our northeastern counties and the
SPC convective outlook keeps a Marginal Risk of severe weather
just to the northeast of Iowa. However, we will be watching over
the next couple days for any signs of southward expansion of
that potential and of POPs in general. As the surface trough
then sinks southeastward across our service area later Tuesday
night, 20% POPs are maintained in that area to account for
lingering showers and storms developing along it, but any severe
weather potential would diminish even further overnight.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 108 PM CDT Sun Aug 23 2026

By Wednesday the large 500 MB heat dome will remain in place
over the southwestern/south central CONUS, while the trough
described in the SHORT TERM section above moves away to our
east. This will allow deep-layer ridging to reassert itself just
to our west, leading to a period of dry, quiet, and seasonally
mild weather with daily highs in the low to mid-80s for the
remainder of the week. By Friday and Saturday the pattern will
begin to shift a bit, as two large 500 MB lows develop over
Canada and shunt the ridge southward, with the heat dome
retrograding more over the far southwestern CONUS near Arizona
and New Mexico. This will cause 500 MB flow over Iowa to become
more zonal, with multiple shortwave impulses moving through the
flow and providing several opportunities for thunderstorms from
Friday or Saturday into early the following week. While the
details of any such storms are very uncertain at this range, it
is fair to say that overall the weather pattern will be more
active by next weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1046 PM CDT Sun Aug 23 2026

Confidence in patchy fog tonight is increasing at KOTM/KFOD, though
still below 50% and will only be added with amendments as needed.
Shower chances between 12z-18z still remain low and minimally
impactful at 10-20% at KFOD/KDSM.

&&

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

&&

$$

SHORT TERM...Lee
LONG TERM...Lee
AVIATION...De Bruin