616
FXUS63 KDMX 101132
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
632 AM CDT Wed Sep 10 2025

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

.KEY MESSAGES...

- Scattered showers linger in northeast Iowa early this morning
  with patchy fog developing behind the shower activity.

- Warming into the upper 80s and low 90s late this week and
  through the weekend into early next week.

&&

.UPDATE...
Issued at 253 AM CDT Wed Sep 10 2025

Scattered showers linger across northeast Iowa early this morning
and will continue to diminish through sunrise. Behind this wave,
clearing skies and light winds have allowed for patchy fog to
develop across parts of northern Iowa. So far dense fog has
largely been contained to Minnesota and far northwest Iowa,
however as cloud cover across north central Iowa diminishes
through the morning, expansion is possible. Given current
observations all over 1 mile, there is no dense fog advisory in
effect, but will be monitoring closely should one be needed
later this morning.

Also moving into the area behind the departing system is upper level
smoke which will make for hazy skies through today. This smoke is
expected to remain aloft. With a lingering thin layer of low level
moisture around, expect daytime cumulus to develop across the area.
Additional patchy light fog is possible across northern Iowa again
on Thursday morning.

Our attention then turns to the building heat for the end of the
week and through the weekend into early next week. Temperatures will
warm through the upper 80s to the low 90s by Friday and through at
least Monday. As has been discussed in the previous couple
discussion/update cycles, an over mixing bias in the GFS is
resulting in anomalously high temperatures that can skew
temperatures much too high in setups like this. Temperatures
through the extended have been nudged down to correct for some
of the introduced bias, consistent with previous adjustments.
Aside from the heat, the forecast through the extended remains
dry. A western US trough will deepen through the weekend and
weak embedded shortwaves may eject out and across the area but
the signal is weak. The better chance for any precipitation
across the area arrives later Sunday into Monday.

&&

.DISCUSSION...
Issued at 253 PM CDT Tue Sep 9 2025

Short wave moving across southern Minnesota has been evident as
circulation on both radar and satellite. Convection has been most
prevalent to the east of the short wave where the greatest forcing
resides but some weak convection continues to percolate over parts
of north central Iowa. This scattered convection will remain
possible over northern Iowa into early this evening and there is a
chance some lingering kinematic forced showers and isolated storms
occur over the far northeast overnight. The other forecast challenge
overnight is fog potential. Higher dew points in the upper 50s to
lower 60s along with a wetting rainfall over the north and light
winds may lead to some fog development. The amount of cloud cover
overnight is a bit uncertain as there is a mix of clear patches and
patches of stratocumulus this afternoon. The stratocumulus should
thin with the loss of diurnal heating but it will be a slower
process than general cumulus. Cumulus should reform early Wednesday
morning as the low level moisture lifts and forms cumulus.

Currently have Wednesday dry as a modest elevated mixed layer (EML)
forms and should prevent convective development but will continue to
monitor the status of the EML. Should the EML remain weak enough for
surface based instability, the overall forcing is quite low but it
would still lead to an isolated shower/storm chance.

The remainder of the forecast has the upper level ridge moving more
eastward and eventually over Iowa for the end of the week and into
Saturday. Have continued the trend of using the NBM 50th percentile
compared to the straight up NBM which is over the 90th percentile.
Note the NBM has not verified well all year when sitting above the
90th percentile. This appears to be another case for that trend. The
850 mb temperatures in the upper teens to low 20s C and dew points
in the upper 50s to low 60s do not correlate to highs in the low to
mid 90s. The GFS is way over mixed this time period while indicating
mostly cloudy skies, which is another red flag. The upper ridge will
move slightly east late this weekend as a negatively titled trough
extends into the state, bringing increasing precipitation
chances.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 632 AM CDT Wed Sep 10 2025

Patchy dense fog has developed across northern Iowa this
morning, impacting KMCW and more recently KFOD. This is expected
to diminish later this morning. Thereafter, VFR conditions will
prevail across all sites. Some diurnally driven cumulus is
expected to develop this afternoon. Light and variable wind this
morning will gradually become light and out of the northeast by
late this afternoon.

&&

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

&&

$$

UPDATE...Hagenhoff
DISCUSSION...Donavon
AVIATION...Hagenhoff