475
FXUS63 KDMX 051140
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
640 AM CDT Sat Jul 5 2025

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

.KEY MESSAGES...

- Several rounds of thunderstorms possible today into this
  evening. A few strong storms with the potential for damaging
  winds may occur this afternoon and evening. Locally heavy rain
  possible throughout the day.

- Periodic thunderstorms from late Monday and through next week.

- Highs mainly in the 80s through the period.

&&

.UPDATE...
Issued at 414 AM CDT Sat Jul 5 2025

A short wave moving towards the state has tilted the upper flow more
southwesterly overnight and this has allowed the low level jet to
tilt into the state. The low level jet will bring deepen
saturated profiles into Iowa today. In fact there is a narrow
ribbon of 2+ inch PWATs stretching from the Texas Gulf coast and
through Iowa to Lake Superior. That is over 200% of normal for
early July and once this deeper moisture arrives, it will limit
the instability this morning. Warm cloud depths to reach over 14
kft so efficient rainfall is expected this morning. The main
short wave and cold front will arrive later this afternoon.
While profiles do dry out in the mid-levels more and the mid-
level lapse rates do steepen more allowing for greater
instability. A few strong storms with damaging wind potential
are possible into this evening. There is very little deep layer
shear with direction and winds speeds nearly uniform through the
layer. The lack of shear will likely lead quick outflow with
new storms developing on the outflow of previous storms. Storm
motions at less than 30 mph could lead to lead to quickly
accumulating rain under the heavier storms. Overall, the threat
for flooding or flash flooding is low given the time of year and
the recovery time since the last heavy rain. Storms are
expected to be mostly out of the area by 06z.

No major changes beyond today. Weak high pressure ridging will be
over Iowa on Sunday. The atmosphere with have some convective
instability with little to no capping but there is not expected to
be a trigger for vertical ascent. Periodic chances for thunderstorms
will occur next week beginning late Monday. A few bouts with strong
storms is likely during the period.

&&

.DISCUSSION...
Issued at 230 PM CDT Fri Jul 4 2025

It`s been a beautiful Independence Day so far, with photogenic,
cumulus filled skies, warm temperatures, and breezy winds. Dewpoints
have stayed a bit more steady today, thanks to the better
mixing/breezier winds helping to disperse the corn`s moisture.
Temperatures are in the upper 80s and will make a run for the
low 90s, but still a degree or two less. All this to say, heat
indices should be a bit more manageable compared to yesterday,
peaking in the mid to upper 90s. Tough to draw up a better
summer day for holiday plans, especially those that involve a
body of water!

This warm summer day comes thanks to a narrow upper level ridge
parked over Iowa, which will slowly drift eastward as an upper level
wave ejects around it from the west. As this occurs, a better fetch
of gulf moisture will pivot into western Iowa. This moisture,
combined with warm south southwesterly flow and synoptic forcing
around the wave will bring the return of shower and thunderstorm
chances beginning late tonight into early Saturday morning. The
overnight/early morning storms will be elevated and only working
with around 1000 to 1500 J/kg of most unstable CAPE, which should
help limit severity. This is especially true with warm and moist
vertical profiles which will inhibit large hail production.
That said, with 1000+ J/kg instability, can`t rule out at least
small hail with stronger updrafts. Likewise, wind can always be
sneaky overnight, even with elevated storms. DCAPE values
overnight will still be over 1000 J/kg out ahead of any storms,
so could certainly see some gusty winds out of storms into the
morning. Fortunately, weak, unidirectional flow through the
column will limit the amount wind shear overnight and into the
morning, decreasing the risk of organized storms/widespread
severe weather.

As the wave continues northeastward through tomorrow, a cold front
will be pulled through the state, eventually firing off a second
round of storms in northwest Iowa as the atmosphere continues to
destabilize through mid-day. This roughly southwest to northeast
oriented line will make its way southeastward through the afternoon
and evening hours, bringing storm chances to most of the state.
Instability values will work to recover from any residual morning
storms, eventually increasing to the 1500 to 2000+ J/kg range by the
afternoon. This will increase the chances for stronger storms, but
the flow through the column never really improves through Saturday
afternoon. With a lack of any shear, strong, organized storms appear
unlikely, but the risk for a few severe wind gusts and hail remains,
especially as storms initially develop. Due to the unstable, but
weakly sheared environment, cold pools will also struggle to stay in
balance. This will likely lead to storm outflows outrunning the
synoptic boundary and coincident convection, limiting the wind
threat with any storms behind the outflow. The storm prediction
center has a marginal risk for severe weather over the area,
reflecting this weakly sheared but unstable boundary passage. In
addition to the severe weather chances, heavy, efficient rainfall is
possible with any thunderstorms. Convection should be progressive
enough to avoid prolonged periods of heavy rainfall over one area,
but will still be monitoring for potential hydrological impacts due
to heavy rain.

The boundary will depart the southern portions of the area by around
midnight tomorrow night, leaving generally dry and slightly cooler
conditions on Sunday. Unfortunately, this will only be a brief break
from precipitation as next week again looks active with zonal to
northwesterly upper level flow overhead with multiple shortwaves
producing convection in vicinity to the state. The next chances in
proximity to the state look to be late Sunday into Monday, but
predictability is quite low in these zonal flow regime.
Therefore, the important takeaway is more active weather with
multiple thunderstorm chances around the state lasting through
the remainder of the forecast period.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 637 AM CDT Sat Jul 5 2025

Periodic showers and thunderstorms are expected at all locations
today into this evening. MVFR to local IFR cigs and vsbys are
also expected with the precipitation at times. Southerly winds
to begin the period will gradually turn more west to northwest
as a cold front enters the state. The precipitation will be
ending by late this evening though MVFR cigs could linger beyond
that.

&&

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

&&

$$

UPDATE...Donavon
DISCUSSION...Dodson
AVIATION...Donavon