922
FXUS63 KDMX 261123
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
623 AM CDT Fri Jun 26 2026

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

.KEY MESSAGES...

- Light showers and possibly a brief thunderstorm are forecast
  across southern Iowa today (20-40% chances of rain), but any
  rainfall will be spotty and generally light.

- More showers and storms are forecast late Saturday and
  Saturday night. A few severe storms may be possible during
  this time.

- Hot and Humid weather arrives Sunday and will persist much of
  next week. Heat headlines will likely be needed at times.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 103 AM CDT Fri Jun 26 2026

A 500 MB shortwave impulse is traveling eastward across the
region this morning, resulting in expanding cloud cover and
broad but weak forcing for ascent. At the surface however, a
warm front remains well to our south across Kansas and MIssouri,
with a high pressure area anchored over the western Great Lakes
region extending its influence into Iowa. This is resulting in
light winds and a layer of drier air that is helping to undercut
any developing precipitation, resulting in light and spotty
radar echoes that are only intermittently reaching the ground
and producing any measurable rainfall. Once such area is in our
southeastern counties and adjacent portions of Missouri and far
southeastern Iowa, while another is moving over the tri-state
area of NE/SD/IA and into northwestern Iowa. Some short-range
models and CAMS still attempt to expand and intensify the former
area of rain across southern Iowa early this morning and even
lingering through today into tonight in some cases, but it is
more likely that any appreciable moisture will remain cut off to
our south where the nocturnal LLJ is focused around the
aforementioned warm front. Have thus trended PoPs a bit further
downward and southward in our southern counties, maintaining
just 20-40% rain chances with light QPF. Also included a couple
hours of slight chance (20%) rain chances in our northwestern
counties in deference to the light echoes approaching from
Siouxland, but these should fade out as the morning progresses.

Aside from PoPs, the other notable sensible weather today will
be in the form of relatively cool temperatures once again, due
to the light surface flow and prevalence of cloud cover. Late in
the day as the 500 MB impulse begins to move off to our east,
low-level flow will come around to southeasterly in our
northwestern counties and some breaks in the clouds may occur
there, so have maintained highs near 80 in that area. In our
east and southeast, however, clouds will linger along with
possibly a light shower or two, and have notched temperatures
down another degree or two into the low/mid-70s in those areas
accordingly.

On Saturday a 500 MB ridge will start to become established
across the central U.S. and Midwest, bringing in warmer
temperatures aloft. This will also induce the Great Lakes
surface high to retreat eastward while a broad surface low
pressure trough develops along the lee of the Rockies. Surface
winds will come around to southeasterly across all of Iowa and
temperatures will rise modestly, peaking in the lower 80s in
most of our forecast area. This will herald the beginning of a
notable and rapid shift in the weather pattern, making Saturday
the last day of relatively comfortable temperatures before a
much hotter period begins as discussed in the LONG TERM section
below.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 232 PM CDT Thu Jun 25 2026

The extended forecast weather story remains the upcoming pattern
change and the arrival of summer heat. As discussed for several
days now, the combination of upper low pressure moving into the
Pacific Northwest and sub-tropical high developing over the
lower Mississippi Valley will create steepening southwest flow
and strong warm advection across Iowa late Saturday and Saturday
night. A few elevated thunderstorms are possible but the
moisture advection portion of the theta-e advection may be
limited. This could lead to the elevated mixed layer becoming
established more quickly and leaving no activation point for
convective initiation. The latest model soundings do show some
potential for storm development over southern Iowa and then lift
north. Any storm development would pose an attendant large hail
threat and potentially damaging winds should any gravity wave
interaction occur.

The impending heat then is the main weather focus for Sunday and
through much of next week. A stout EML will be in place on Sunday.
The main upper level energy begins to eject northeast out of the
Pacific Northwest on Monday and will force a boundary westward.
There remains a low chance that the boundary moves far enough east
for thunderstorm chances to reach northwest Iowa late Monday and
Monday night. The upper low will flatten the top of the upper ridge
mid next week and may bring a brief periods of ring of fire MCS
development that could impact northern Iowa. This could also impact
high temperatures into that part of the state mid-week and bring a
brief reprieve to the heat before it resumes for the entire state
moving into the end of the week and into the holiday weekend.

High temperatures by the NBM Sunday and early next week may be a
touch high though it is currently running with a cooler bias due to
recent weather. In addition, northwest Iowa has been relatively dry
this month and that will also be the region closer to the thermal
ridge so if good mixing occurs, temperatures may approach these
values. As noted above, the EML will be in place at times and that
will limit the mixing depths to below 850 mb at times so despite the
impressive 850 mb temperatures in the mid 20s Celsius range, these
may not be fully realized at the surface as those may remain in the
EML area. Dew point values are more interesting. The Gulf flow
becomes wide open into Iowa and dew points well in the 70s have
resided in the recent warm sectors to the south that had access to
Gulf flow. In addition, evapotranspiration of the Iowa crops is
beginning to take off now that rapid growth rates are now taking
place. This will further accelerate next week. Therefore, dewpoints
well in the 70s are likely as moisture becomes trapped below the EML
with limited options to mix these out. Raw model guidance from the
NAM/GFS/ECMWF/SREF have 75+ dew points for Sunday afternoon as a
theta-e plume moves across the state. The combination of these
higher dew points and high temperatures in the 90s, will create heat
index values above 100 common from Sunday through much of next week
and will require heat headlines at times as we move into a prolonged
period of heat.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 623 AM CDT Fri Jun 26 2026

VFR conditions will prevail through the TAF period. A few light
showers or sprinkles will affect the area early this morning,
but any visibility reductions will be brief and minimal. On
Friday morning, right at or just before the end of the 12Z TAF
period, MVFR ceilings may be possible at DSM and OTM but
probability is currently too low (30% or less) to advertise in
the TAFs at this range, and potential will be re-evaluated for
later updates.

&&

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

&&

$$

SHORT TERM...Lee
LONG TERM...Donavon
AVIATION...Lee