889
FXUS63 KDMX 191724
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1224 PM CDT Wed Aug 19 2026

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- Thunderstorms are expected over parts of central and southern
  Iowa, mainly south of Interstate 80 today into this evening. A
  few strong storms with large hail and damaging winds may
  occur. Locally heavy rainfall of 1-3 inches is possible over
  far southern Iowa.

- Addition storms possible Thursday night and again Friday
  night.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 255 AM CDT Wed Aug 19 2026

The main surface boundary has settled well to the south of Iowa and
is over southern Kansas and Missouri early this morning. An intense
low level jet (LLJ) has led to vigorous storms from Topeka to Kansas
City and southeastward. A few showers and an isolated thunderstorm
have been ongoing over far southern Iowa. High pressure moving into
Minnesota with drier air moving into northern Iowa while mid-level
moisture continues over southern Iowa. This has led to a moisture
discontinuity over the state with PWAT values dropping below 0.75"
north while remaining over 1.50" far south. Water vapor imagery and
RAP Potential Vorticity 1.5 pressure surface analysis show a robust
PV anomaly/short wave cluster moving from southeast Montana and into
western South Dakota. This anomaly is stronger than previously
expected the past 24-48 hrs and will lead to a more active weather
day for parts of Iowa.

Intense storms have developed in advance of upper level system over
south central South Dakota. The MUCAPE axis ahead of these storms
does lead into southern Iowa storm motions indicators such as the
Corfidi vectors and 850-300 mb winds, suggest these storms may
follow the instability axis and into the state later this morning.
The various CAMs continue to be hit or miss today and much like
their performance for much of August. Conceptual model would place
thunderstorms across southern Iowa today, with the potential for a
few strong storms with large hail and/or damaging wind gusts.
Assuming this mornings cloud cover will erode enough for
destabilization, surface based convection is certainly possible.
Organized storms are possible but there is no shear in the lowest 10
kft with very light winds present then overtopped by increasing
speed shear. Even without the surface instability, sufficient
instability aloft and potential for free parcel lift is expected for
storm potential as static stability is low. Locally heavy rainfall
is possible as well and WPC has placed a slight risk for Excessive
Rainfall. That said, any heavy rainfall will likely be over far
southern Iowa and an area that hasn`t had much rainfall the past 72-
96 hrs. The storm potential will persist over southern Iowa through
the evening hours and until the upper PV anomaly passes by.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 231 PM CDT Tue Aug 18 2026

Upper troughing over the eastern half of the CONUS continues for the
foreseeable future with a ridge over the southwest. By the
weekend, the ridge builds over the western U.S. while the trough
deepens over the eastern U.S. A closed low looks to develop
over the Great Lakes eventually shifting eastward into early
next week while another low drops out of Canada and towards the
Great Lakes early next week as well. The end result is we remain
in upper northwest flow never fully getting under the upper
ridge keeping the forecast relatively active with several
chances for precipitation through the weekend and beyond. The
closest we get to the upper ridge is Saturday into early Sunday
which looks to be one dry period. Another is before that, later
Wednesday night through much of the daytime Thursday as a
surface high pressure moves across, and then again towards mid
to potentially later next week when a longer stretch of drier
weather may finally take hold. Shortwave energy will precede a
cold front which moves through the area on Friday bringing the
return of precipitation chances from around Thursday evening
through a good portion of the day Friday, though it won`t be
raining everywhere during this entire stretch. The best moisture
return looks to be over Nebraska into western Iowa and southern
Minnesota Thursday night and then maybe more into Iowa on
Friday. We never fully get an open Gulf during this timeframe,
and lower level moisture is also cut off from the Pacific stream
despite mid-level moisture much healthier. All this to say, the
best (stronger) storm chances are in far northwest Iowa which
aligns with the SPC Day 3 Marginal (Level 1 of 5) risk which
runs until 7 AM Friday. Temperatures remain pleasant this week
in the the 70s to 80s with slightly warmer temperatures (still
in the 80s) on Friday ahead of the cold front pending cloud
cover and shower/storm timing from the night before.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1224 PM CDT Wed Aug 19 2026

VFR cloud cover is in place across much of Iowa this afternoon.
Meanwhile, a complex of storms is moving across Nebraska. These
storms will reach southern Iowa later this afternoon, expected
to move across southern Iowa late afternoon into this evening.
Most likely impact is at KOTM where a prob30 is included. The
track looks to remain south of KDSM, so have removed any thunder
mentions from the TAF there. Otherwise, light wind from the
northeast for much of the period.

&&

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

&&

$$

SHORT TERM...Donavon
LONG TERM...05
AVIATION...Hagenhoff