368
FXUS63 KDMX 161143
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
643 AM CDT Wed Jul 16 2025

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

.KEY MESSAGES...

- Rain and storms to clear out faster today, with a heavy rain
  setup possible in southern Iowa tonight (60% confidence in
  rain).

- Multiple chances of heavy rain this weekend. Slight Risk ERO
  out for multiple days in a row.

&&

.UPDATE...
Issued at 239 AM CDT Wed Jul 16 2025

An MCS moved into Iowa ahead of schedule overnight with most of the
model guidance available initializing too far west geographically.
Have translated this discrepancy into the PoPs by accelerating the
departure of precipitation by about 2 hours. The line of storms that
moved through Omaha zapped the main instability axis as expected, so
the severe threat in the short term dwindles. Could see some gusty
winds where the line of storms latches onto the warm front. Another
feature of note is an MCV that has formed in Northwest Iowa. This
will keep precipitation going across the north through the morning
hours. Scattered convection will also be possible immediately
ahead of the MCS due to the LLJ angled into the state.

The main baroclinic zone will move across the state during the
daytime and usher in dry air from behind, this being the culprit for
such cool low temperatures across the north Thursday night. Its
trailing cold front will stall somewhere near the IA-MO state line
tonight. The mean wind and LLJ will have similar direction and will
be blowing parallel to the stalled front, appearing similar to a
Maddox frontal pattern for heavy rain. Corfidi vectors point
parallel to the orientation of the front, meaning there will be
training storms in a prime heavy rainfall environment. PWATs upwards
of 2.5" with warm cloud depths over 4000m are collocated. Soundings
also have a long, skinny CAPE profile in the warm sector, helping
lift parcels evenly throughout the profile. While most guidance
keeps the heaviest rainfall south of the state for now, have still
preserved PoPs in the overnight period for southern Iowa. The
thinking is that location issues could persist through the entire
model run. The surface low this afternoon could be further northeast
than what is displayed, meaning it would have pulled its cold front
further north. The RRFS supports this thinking, the 00z run being
one of the models closer to spatial reality. It has the H850
boundary firing off in the bottom row of Iowa counties, producing
over 2 inches of QPF along the way. In this regime, there will be
spots along the front that overperform, making a push at 5 inches.

High pressure gives us a brief pause on Thursday and gives us
comfortable temperatures in the process. Highs will only be in the
70s. All eyes then turn to the weekend as that stalled boundary
doesn`t really go anywhere, and it will be subject to upper-level
northwest flow as well as an open plume of Gulf moisture aimed
near the state. The upper-level jet comes into play come late
Saturday, so add some deep-layer shear to the mix.

&&

.DISCUSSION...
Issued at 256 PM CDT Tue Jul 15 2025

Another warm and humid afternoon is ongoing with temperatures in the
80s and dew points in the 60s to 70s resulting in heat indicies in
the upper 80s to upper 90s across the area. Flow out of the south to
southwest will continue to bring in moisture off the Gulf into
Wednesday morning ahead of the approaching low-level low which will
be moving through southern MN through the daytime Wednesday dragging
a cold front with it through the state into Wednesday evening.

Attention first is on the developing convection in Nebraska this
afternoon into evening which will progress eastward towards the
Missouri River into late tonight, maintained in NE by a 30-40 knot
LLJ. The overall parameter space into our far western CWA will make
it difficult for storms to stay in balance with current thinking in
line with previous and recent CAM trends of decaying convection
moving into western Iowa near to after midnight before any lingering
activity continues to push eastward into early Wednesday morning.
Although can`t completely rule out a strong storm as the line
initially enters our far western CWA, overall expecting any storms
to be sub-severe. For any strong storms that can maintain into
western Iowa, strong wind gusts are the primary threat followed by
locally heavy rain, though activity should be progressive enough to
limit the hydro threat overall, especially after several dry days
now.

What remains uncertain is the coverage and timing of the decaying
storm activity into central Iowa and beyond which has significant
implications on the any storm development later in the day
Wednesday. The aforementioned cold front will be drifting southward
through the area through the day and setting up somewhere near the
IA/MO border into Wednesday afternoon. Pending any other lingering
outflow boundaries/mesoscale details after the morning activity,
this is likely where additional development will occur during the
afternoon to evening but this boundary in CAMs is anywhere from
south central Iowa into northern Missouri making it difficult to
pinpoint at this range where the better storm threat is. As noted
yesterday, the better shear lags behind the boundary even though
instability blossoms in the warm sector south of the front. There
remains enough of a favorable environment for a few strong to severe
storms develop in the afternoon to evening, especially over southern
Iowa, if not further south, but at this point remains conditional on
frontal location, amount of early day clearing, and any other
mesoscale details. The primary threat will remain strong wind gusts
and locally heavy rainfall once again, though the potential
placement of rain over southern Iowa is also the area which can take
the most amount of rain given antecedent conditions and continuing
maturing crops. The LLJ is not as robust on Wednesday night into
Thursday, but may help maintain some rain/storms over far southern
Iowa into the night before clearing into Thursday morning.

High pressure drifts into and through the area later Thursday into
Friday with cooler temperatures moving in behind the frontal passage
as well. This will bring some pleasant days to end the week with
temperatures in the 70s to low 80s. Active weather returns late
Friday into the weekend, however, with multiple additional chances
for showers and storms at times. Details remain uncertain at this
range, but will continue to monitor trends.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 642 AM CDT Wed Jul 16 2025

Light rain showers are largely expected to pass across the state
through the remainder of the morning into the early afternoon,
with a chance for a few storms mainly over KFOD over the next
few hours. Otherwise, ceilings across the majority of the state
are expected to decrease further as low clouds pass through,
with MVFR/IFR conditions expected through the rest of the day.
KOTM has the potential to see additional showers this evening
into early Thursday, and maybe a storm or two, though the
confidence is fairly low, thus the PROB30 mention at this time.
Otherwise winds will gradually shift northwesterly across the
state today, with gusts up to 20-25 knots, especially over
parts of northern Iowa.

&&

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

&&

$$

UPDATE...Jimenez
DISCUSSION...05
AVIATION...Bury