156
FXUS63 KDMX 310418
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1118 PM CDT Thu Jul 30 2026

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

.KEY MESSAGES...

- Showers and thunderstorms in the west this afternoon slowly
  move eastward with time tonight. More widespread rain/storms
  are then expected late tonight into early Friday morning.
  There is a chance for some gusty winds but the overall chance
  for severe storms is low tonight. There is a potential for
  heavy rain Thursday night into Friday morning.

- Additional rain and thunderstorms are possible on Friday
  midday into the evening, with an isolated threat for severe
  weather, especially in southeast Iowa.

- Breezy conditions are expected Friday afternoon with wind gusts
  reaching up to 40-45mph.

- Relatively cooler and quiet weather is then forecast Saturday
  through at least Monday.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 252 PM CDT Thu Jul 30 2026

Surface high pressure continues to drift eastward this afternoon as
the first in a series of shortwaves moves into the area. Radar
returns have slowly crept into Crawford and Sac counties over
the last several hours with returns also diminishing as they
creep eastward, thanks to dry air in the low to mid levels. As
time goes on, profiles do start to saturate so it is possible
western to northwestern counties do start to see some light rain
this afternoon to early evening as the first shortwave pushes
east into tonight. Prior to saturation occurring, profiles show
the inverted V soundings so an isolated strong wind gust remains
possible with the shower activity as it reaches our western
area, but overall the severe threat remains low this afternoon
with limited CAPE/Shear in the bulk of the area. As this
saturation occurs, these showers will then likely percolate
across portions of western and into northern and central Iowa
through the evening posing mainly a heavy rain threat as they
will be slow moving. The bulk of this rain initially looks to
fall in western Iowa, just outside of our area.

Attention then turns towards the activity developing in NE/SD this
afternoon, as these are the storms we are monitoring as they near
our area late tonight. Although there remains some overall agreement
in storms diminishing in intensity as they reach into our area late
tonight/overnight, there is less confidence in the track of the
storms with some recent guidance sinking them southwest, others
right through the area, and then even less acquirement amongst
CAMS in timing with many suggesting a slower evolution while
others still have most activity through between 06-12Z (1AM to
7AM). There remains some idea of the storms congealing into a
line but should they dive southwest, there may then be a spatial
break between the diminishing line of storms and the
percolating activity closer to the low (more on this in a
minute). The timing and strength of this next line of storms has
many implications on the going forecast in 1) QPF/rain
amounts/locations of the highest rain amounts, and 2) the severe
threat to follow on Friday. We`ll get back to this in a second.
What we do know is by late tonight cyclogenesis occurs with a
surface low developing around the IA/SD/NE border. The parent
upper trough and related surface low both cross through the area
through the day Friday, finally departing the state by early
Saturday morning. There is likely to be a break in the activity
between the line late tonight/overnight and the additional
activity developing in the deformation zone on the backside of
the low tomorrow. If there is enough of a break (e.g. the faster
solution noted above), there is a conditional severe threat
that may develop in southern to especially southeast Iowa Friday
later afternoon to early evening provided some clearing can
occur. Sufficient 0-3 CAPE and low LCLs could combine with the
backing flow to create a tornado threat, or at the very least
some funnel cloud potential in addition to a wind threat with
any storms that can develop. Gradient winds on the back side of
the low are expected to increase through the afternoon Friday
with gusts to around 30-45 mph, so it wouldn`t take much to get
an even stronger gust with a storm. If the slower solution noted
above occurs, this could potentially increase rain amounts, but
it makes destabilization much harder and thus decreases the
severe threat Friday afternoon. Rain amounts largely remain in
the 1-3" range, the highest totals looking to be in portions of
northern to eastern Iowa, though isolated higher amounts are
certainly possible in localized areas and should they get closer
to the 3-5" range, especially if in an urban area, this could
lead to some heightened flash flood concerns. The location of
these higher rain amounts remains uncertain, however, with the
increasing variability in location/timing of the showers/storms
through the rest of the day/night tonight into Friday morning.
See the HYDROLOGY section below for some additional details in
the Hydro threat.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 252 PM CDT Thu Jul 30 2026

Drier conditions return on Saturday as an upper ridge starts to
build back into the area. Temperatures remain cooler for the season
and in the 70s Saturday to 80s into early next week making for
another pleasant stretch. The next chances for precipitation start
to move in midweek as upper troughing returns with several rounds
possible as waves move through the overarching upper level pattern.
Details will continue to be fine-tuned as we get closer.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1117 PM CDT Thu Jul 30 2026

Main forecast impact is the showers and thunderstorms moving in
tonight into tomorrow. Initially showers are expected to give way to
a main line of showers and embedded thunderstorms that will move
across the entire state this overnight before clearing out shortly
after 12z. Some uncertainty exists in when the rain will clear out
and a morning break in the rain occurs. The onset of rain will be
associated will lowered ceilings, and there is moderate
confidence in IFR ceilings being reached around morning.
Showers may linger in northern Iowa for most of the day, though
the specific timing is uncertain and is generally handled with
PROB30s. A 2nd less certain round of thunderstorms is expected
in the afternoon tomorrow, particularly in central to southeast
Iowa, and is therefore handled with PROB30 groups as well. Gusty
northerly winds up to 30 knots build in tomorrow afternoon and
evening across Iowa.

&&

.HYDROLOGY...
Issued at 252 PM CDT Thu Jul 30 2026

Risk of flash flooding (initially) and subsequent river flooding
returns to our CWA late in the work week due to aforementioned heavy
rain potential. For the flash flood risk, the most likely QPF
scenario would mainly confine flash flood concerns to urban areas,
where ponding or lower-end flash flooding may occur. Crops in the
rural areas are well into their growth which tends to significantly
increase infiltration capacity. Three potential nuances are (1)
slightly elevated soil moisture percentiles from central into
northeast IA, which would increase the risk of runoff in rural
areas; (2) intense rainfall rates may increase the risk of increased
runoff in rural areas; (3) rainfall that overachieves vs. QPF would
increase the flash flood risk even in rural areas. Rural rain
amounts that exceed ~3-4 inches over a few hours would especially
increase the risk.

River flood risk depends significantly on rainfall amounts, location
and timing. Presently the most likely scenario is moderate to
significant within-bank rises on many streams with a few river
forecast points possibly reaching action stage, but remaining below
flood stage. Rainfall that overachieves vs. QPF would result in
higher stages, with more forecast points reaching minor flooding,
along with some isolated moderate river flooding.

&&

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

&&

$$

SHORT TERM...05
LONG TERM...05
AVIATION...De Bruin
HYDROLOGY...Zogg