999
FXUS63 KDMX 300347
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1047 PM CDT Sat Aug 29 2026

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

.KEY MESSAGES...

- Breezy winds with gusts up to 35 mph possible through late
  this afternoon with a very low chance (<20%) of a few
  isolated showers or perhaps storms.

- Increasing late season heat and humidity Sunday into much of
  next week, especially over southern Iowa where heat index
  values will be around 100 degrees at times.

- By no means a wet period, but there will be additional storm
  chances up to 40% at times tonight into at least the middle of
  next week with peak timing of chances mainly overnight into
  the early morning hours.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 216 PM CDT Sat Aug 29 2026

Numerous features are apparent on GOES-East upper level water vapor
imagery with several cyclonic spins - two along or just off the West
Coast within a mean broad scale trough and another rotating over the
Quebec and Ontario provinces. Our decayed storm system, which
overtopped the mid-level ridge axis which has spread eastward into
the Middle Mississippi River Valley, brought overall welcomed
rainfall due to the recent dryness to northern and parts of central
Iowa. The showers and storms have since largely dissipated or moved
out of central Iowa, though a few spotty showers or isolated storms
remain possible this afternoon. Otherwise, there has been some
clearing, which has allowed for sunshine to turn the
temperatures upward quickly. Highs are on track for the 80s -
around 80 degrees over northeastern Iowa and well into the 80s
to near 90 degrees over southwestern Iowa. Winds have been
breezy as forecast as boundary layer mixing has tapped into the
weakening winds at the top of this layer. Thus, winds have been
sustained between 10 and 20 mph and gusts up to around 30 to 35
mph.

As we head into tonight, the 850mb low level jet will be over Iowa
and nosing into southern Wisconsin. Instability will be lessening
through the night and shear will be lacking such that expectations
are mainly dry overnight. More nebulous ribbons of shortwave energy
will pass overhead in concert with a the weakening nocturnal low
level jet during the day Sunday and this may offer a slightly higher
chance (20-35%) for spotty showers and storms. However, this
activity will be fighting against increasing warm layer capping as
the 500mb heights increase at the same time. This same pattern may
repeat late Sunday night into Monday with the next round of ill-
defined energy topping the ridge with weak instability and shear and
the low level jet once again nosing into Wisconsin. Summarizing,
while there are chances for a few storms tonight through Monday, the
current forecast would have odds favoring a dry forecast for many.
On the temperature side, the increasing heights on Sunday into
Monday spell warmer conditions. However, initial National Blend of
Models (NBM) raised highs 3 to 4 degrees over the previous forecast.
Investigation showed this was above the 90th and 75th percentile
Sunday and Monday, respectively, which pushed highs well into the
90s to even 100 degrees. Part of these warm NBM temperatures may be
due to the influence of the way too warm GFS and its ensemble. For
historical reference, if 100 degrees occurred at Lamoni, this
would be one of the latest 100 degree or higher days on its
record. Thus, forecast high temperatures were tuned down both
Monday and Tuesday in collaboration with southern neighboring
offices.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 216 PM CDT Sat Aug 29 2026

The mid-level ridge will be drifting and lifting northeastward
becoming centered over the St. Louis area by Tuesday. The broad
trough in the western US will persist keeping our low level flow
from the southwest and the storm track passing over northern
portions of the state with a surface quasi-stationary boundary in
place in that vicinity as well. The sensible weather effects will be
drier and warmer conditions over southern Iowa with opportunities
for storm chances over northern Iowa with a timing peaking likely
overnight into the early morning hours. This is not a forecast to be
very specific with fine tuning of the details such as timing and
location in the coming days. What seems more confident is the late-
season heat with potential for several days of record warm low
temperatures possibly in jeopardy, pending any convective
development farther south in Iowa and cloud debris contamination.
While heat index values never breach the 105 degree advisory
criteria, there will be multiple days of values peaking in the 100-
103 degree range over southern Iowa paired with low temperatures in
the upper 70s through at least Wednesday. Experimental heat risk is
in the extreme category (level 4 of max of 4) over many portions of
southern Iowa during this period, which aligns with the magnitude of
the uncommon late season heat and high low temperatures. Those with
vulnerabilities to heat will want to take precautions through this
upcoming week.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1047 PM CDT Sat Aug 29 2026

VFR conditions will prevail through the TAF period. Winds have
diminished for the most part this evening with the low level jet
increasing. This will result in a period of LLWS across all
sites through sunrise. Then Sunday morning scattered
thunderstorms will move across the area, lasting into the
afternoon. KALO and KDSM are the most likely areas to see
precipitation and prob30 groups are included. Scattered
convection is possible at KFOD/KMCW/KOTM however timing is
shorter and less certain, so have kept from TAFs at this time.

&&

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

&&

$$

SHORT TERM...Ansorge
LONG TERM...Ansorge
AVIATION...Hagenhoff