Waterloo, Iowa Weather Forecast Discussion

764
FXUS63 KDMX 092347
AFDDMX
Area Forecast Discussion
National Weather Service Des Moines IA
647 PM CDT Tue Sep 9 2025
...Updated for the 00z Aviation Discussion...
.KEY MESSAGES...
- Scattered showers and isolated non-severe storms mainly north
  into this evening.
- Warning up this week into the 80s mid-week and potentially
  some 90s Friday and into saturday.
&&
.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 /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 647 PM CDT Tue Sep 9 2025
Main aviation concerns are on shower and storm chances over the
next few hours followed by fog and low clouds after midnight
through a few hours after sunrise Wednesday. A few storms over
southern Minnesota may drop into northern Iowa along with
possible additioanl development this evening, but spotty
coverage precludes any PROB30 or otherwise mention at this time
at the northern terminals of MCW and FOD. After midnight, fog
is likely to develop with low ceilings also possible with
impacts down to MVFR and IFR at FOD/MCW. While fog will
dissipate by 14z and ceilings are expected to scatter, they will
be gradual to lift to above FL030, which may not occur until
afternoon at MCW and perhaps ALO.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...Donavon
AVIATION...Ansorge

NWS DMX Office Area Forecast Discussion