466
FXUS63 KDMX 301150
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
650 AM CDT Thu Jul 30 2026

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

.KEY MESSAGES...

- Showers and thunderstorms return to the area with low (20-30%)
  rain chances in the west Thursday afternoon/evening, then near
  100% chance of rain Thursday night. There is a low chance of
  severe weather in western Iowa during the day, but a more
  widespread potential for heavy rain Thursday night into Friday
  morning.

- Additional rain and thunderstorms are possible on Friday, with
  a isolated threat for severe weather. Relatively cooler and
  quiet weather is then forecast Saturday through at least
  Monday.

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

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 402 AM CDT Thu Jul 30 2026

After a benign Wednesday, big changes will arrive today. We kick off
this morning keeping an eye on a mid level shortwave trough
positioned over northern South Dakota. Current satellite imagery
reveals a cluster of showers and non-severe thunderstorms over
northern Nebraska and southern South Dakota, currently thriving on
rich low-level moisture and moderate MLCAPE values. However, as
these storms continue to push eastward, they are expected to run out
of steam upon entering a more stable airmass characterized by mid
level dry air. Now one thing worth noting is, if these storms can
survive as they enter western IA, due to the dry air in the mid to
low levels, could enhance evaporative cooling and yield a gusty wind
threat. This will be something to monitor through the morning if
instability can persist longer than guidance suggests.


Attention then shifts to a more widespread convective and heavy rain
event Thursday night into Friday. Initial shower and thunderstorm
development will take place along a cold front over in the Central
Plains Thursday afternoon. Convection is expected to quickly
consolidate into a linear complex, entering our area late Thursday
night into early Friday morning. Damaging winds will be the primary
threat with this line of storms as it enters western Iowa, but
severity will wane as the system tracks east and encounters less
instability over central Iowa. Still, an isolated damaging wind
threat could linger in western Iowa before the line diminishes.
Outside of the severe risk, abundant deep-layer moisture will also
accompany the system, presenting a heavy rainfall and potential
flash flooding threat. Further details are available in the
HYDROLOGY section below.

A second round of active weather remains possible on Friday, though
confidence in specific details is lower. The evolution of the
surface low driving Thursday night`s rainfall will play a critical
role in Friday`s severe threat. While the primary line of showers
and storms should exit the area Friday morning, secondary convective
development remains possible on the backside of the low. Meanwhile,
guidance indicates some clearing from Des Moines southward across
southern Iowa. This corridor will be closely monitored, as airmass
recovery following morning convection could support strong to severe
thunderstorm redevelopment. Models suggest a thin stripe of SBCAPE
values recovering to 1500-2500 J/kg within this destabilizing warm
sector and ahead of the cold front. Additionally, strong surface
cyclogenesis will foster enhanced low level helicity; paired with 03
km CAPE around 150 to 200 J/kg and low LCL heights, stretching could
yield a conditional threat for a few tornadoes. Ultimately, this
risk is highly conditional on daytime clearing. Lingering morning
clouds or rain would limit boundary layer destabilization and
quickly suppress the severe threat.

Also of note with this system passage on Friday will be the
potential for some gusty synoptic winds wrapping around the back
side of the passing surface low. This will first be noted over
northwest Iowa Friday afternoon, before tracking south and east
through the evening. Wind gusts of 30 to 35 mph are expected, with
some even stronger gusts over 40 mph possible as downward momentum
is enhanced by the drying precipitation field.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 156 PM CDT Tue Jul 28 2026

By Friday night the low pressure system discussed in the SHORT
TERM discussion above will be departing to the east/southeast,
with some showers and perhaps a few thunderstorms lingering into
the night before likewise departing. By Saturday the
southwestern U.S. deep-layer ridge will have been shunted
westward by the trough deepening over the central U.S., being
centered somewhere around UT/AZ/NV by Saturday afternoon. This
will result in cooler northerly mid-level steering flow over
Iowa. Meanwhile, a surface ridge will build down the Upper
Midwest in wake of Friday`s low pressure system, bringing modest
northerly breezes to Iowa by Saturday, then variable winds later
in the weekend. While Friday temperatures will thus be generally
cool due to rain and cloud cover, this weekend will present a
more enjoyable "cool" weather spell with clearing skies,
generally light winds, and highs in the low to mid 80s. This
will be a far cry from the intense heat experienced across the
region last weekend!

Next Monday will be largely the same as the weekend, with highs
around the low to mid-80s, mostly sunny skies, and light winds
as the surface ridge begins to move away to the east late in the
day. Another surface trough/front will then approach from the
Dakotas on Monday night and Tuesday, then stall out somewhere
across the region around the middle of next week. Just after
this, a broad 500 MB trough will round the base of a large gyre
over Canada, passing through the Upper Midwest and providing
some modest forcing for ascent sometime between Tuesday night
and Thursday or so. This is a classic set-up for multiple rounds
of showers and thunderstorms along the stalled frontal zone,
however, it remains to be seen where that will occur or how the
timing and details will shake out. At any rate, after a dry
period from Friday night or Saturday through at least Monday,
some chances for rain will return around the middle of next
week.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 642 AM CDT Thu Jul 30 2026

VFR conditions to prevail through Thursday evening. A few
showers and storms will build in western Iowa this afternoon
around 18z but showers are not expected to impact terminals.
Confidence is higher that showers and a few storms will impact
terminals early Friday morning starting at 03z until the end of
this TAF period. Ceiling and visibility restrictions may occur
during heavy rain showers and thunderstorms.

&&

.HYDROLOGY...
Issued at 121 PM CDT Wed Jul 29 2026

Potential for heavy rainfall Thursday night into Friday morning
as thunderstorms move across the area. NAM solutions depict very
deep warm cloud depths around 5 KM and PWAT of 2.4-2.5"
supporting very efficient rainfall processes. However, most
other model solutions are a bit less extreme with warm cloud
depths of 3-4 KM and PWAT of 2.0-2.1", which still support some
heavy rain threat but not quite as alarming. In addition, there
is broad consensus that the main swath of showers/storms moving
through the area Thursday night will be progressive, limiting
overall rainfall amounts and precluding any widespread Flood
Watch at this time. That being said, with efficient rates
likely, any deviant motion or backbuilding storms could lead to
localized heavy rainfall amounts.

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 gotchas 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 possibly up to a few river forecast points
reaching minor flooding.

&&

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

&&

$$

SHORT TERM...TDR
LONG TERM...Lee
AVIATION...TDR
HYDROLOGY...Zogg