619
FXUS63 KDMX 200418
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1118 PM CDT Sat Sep 19 2026

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

.KEY MESSAGES...

- Scattered showers and storms this afternoon into evening, with
  more widespread rainfall over central and southern Iowa
  tonight into early Sunday morning. A few stronger storms could
  produce strong winds, hail and heavy rainfall.

- Cooler temperatures with light rain and drizzle persists on
  Sunday.

- Cool temperatures and moist weather persist into Monday, with
  drier conditions expected Tuesday and Wednesday.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 255 PM CDT Sat Sep 19 2026

This morning`s weather was quite reminiscent of yesterday`s with
stratus and fog impacting much of the area, and lingering overnight
showers and storms. The stratus has remained firm across northern
Iowa today and will likely stay that way through the evening into
tomorrow morning. Patchy fog is still present at a few sites in
northern Iowa, but not nearly to the extent it was earlier this
morning. In southern and central Iowa, a bit more sunshine is being
observed where clouds have cleared out, although isolated showers
and occasional storms have persisted. This activity has been heavily
localized and transient.

Through the remainder of the afternoon, occasional showers and
thunderstorms are expected to bubble along a southwest to northeast
oriented boundary drifting southeastward through the area. While
there is a modest amount of instability (1500 to 2500 J/kg) ahead of
this boundary, convergence is fairly weak and wind fields are
meager. Most of the better shear resides behind the boundary with
less than 30 kts of effective shear out ahead of it. There is a
pocket of 25 to 30 kt shear along the I-80 corridor, coinciding with
the nose of the unstable air, which could favor a few stronger
storms capable of producing hail or damaging winds this afternoon
into the evening.

The aforementioned surface boundary will sag southeastward into the
evening, eventually departing the state late tonight. However, a
weak low level jet developing overnight will bring moisture and
ascent over the sloping air mass. Assisted by lift from a subtle
shortwave, this LLJ will bring another surge of showers and
thunderstorms tonight (generally around midnight) into early Sunday
morning. Storms are expected to track roughly parallel to the
boundary across central and south central Iowa, but remain semi-
progressive as the wave pushes through. Since this activity will be
elevated and behind the surface boundary, it will have excess to the
slightly higher shear environment mentioned earlier. However, by
this time of night, instability will also be waning. Can`t
completely rule out a few stronger storms, especially early in the
night, but the risk will be diminishing. That said, with storm
motions parallel to the boundary and abundant moisture, heavy
rainfall will once again be possible. More on the heavy rain and
hydrologic concerns in the hydro discussion below.

As we get to sunrise Sunday, the convective activity should be all
but moved out, barring any lingering showers or storms along the
Iowa/Missouri border. High pressure and cooler temperatures will be
filling in with the northerly flow pattern, but will result in
widespread stratus and drizzle as a rare easterly low level moisture
transport plume keeps the low levels moist. With marginal
instability in the layer (less than 500 J/kg) a few convectively
driven showers are possible through Sunday as well, but values will
be low enough to eliminate any severe weather risks. With cloudy,
cool, moist, and drizzly conditions Sunday into Sunday night, the
conditions in Iowa will appear more reminiscent of what most of
us consider "fall weather".

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 255 PM CDT Sat Sep 19 2026

The cooler, fall-like conditions continue into Monday and early next
week with highs generally only reaching the upper 50s to near 60
both Monday and Tuesday. Our light rain generally continues into
Monday, this time with a bit more synoptic support as a an upper
level low meanders into Iowa trudging along in the zonal upper level
flow. This low hangs out overhead into Tuesday, but begins to
bring drier air into the state. Should this pan out as the
models suggest, we should finally see a few dry days Tuesday and
Wednesday of next week. However, rain chances do look to return
to at least western Iowa on Thursday. More details on that in
the coming days.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1117 PM CDT Sat Sep 19 2026

Mainly IFR stratus sits over central and northern Iowa this
evening with gradually lowering ceilings, possibly approaching LIFR.
A few sites have had fog as well, and it may increase in coverage
tonight, though confidence is low and CIGs will be the greater
impact. Thunderstorms are also ongoing near KDSM and KOTM and will
continue for several hours, possibly impacting KALO after 7z.
Conditions for widespread drizzle look possible through most of the
day tomorrow, with the two most likely windows seemingly between 14-
17z and 21-03z. Confidence is low regarding vis impacts so this was
handled using prevailing -DZ 6SM with PROB30 2SM for this issuance.

&&

.HYDROLOGY...
Issued at 312 PM CDT Sat Sep 19 2026

The moisture rich environment overhead will bring yet another night
of heavy rain potential to the state, this time central into
southern and eastern Iowa. The weather prediction center has placed
a moderate risk (level 3 of 4) for excessive rainfall to our east,
while most of the DMX forecast area resides in a slight risk (level
2 of 4) or a marginal risk (level 1 of 4). Most of the precipitation
expected tonight will develop with the low level jet oriented
roughly parallel to the boundary, supporting some training storms
and potential for prolonged moderate to heavy rainfall. However, CAM
guidance suggests storms could be fairly progressive, rather than
camping over one area for a long period of time. Likewise, HREF for
1" per hour rates are near-zero, likely thanks to the waning
instability by the time these storms develop. QPF output generally
ranges from 1 to 2" with some pockets getting closer to 3" in a few
models. While this could lead to some ponding issues, or even minor
flash flooding should one of the 3" bullseyes align with an urban
area, have decided to hold off on a Flash Flood Watch at this time.
With the low probability for 1" per hour rates and potential
progressive nature of the rainfall, confidence isn`t high enough at
this time.

As for river flooding, heavy rain in Minnesota last night has
resulted in responses on rivers upstream from the Cedar River basin.
As a result, water routing down through these basins will likely
lead to rises into action stage early this week along the Cedar
River, specifically ALOI4 and CEDI4. At this time, flooding is not
expected and any additional rainfall today and tonight should fall
south and east of these rivers basins. However, upstream
observations will be monitored closely as water routes into the
rivers and information will be provided should anything change.

For tonight, rainfall amounts of 1 to 3" should generally only cause
in-bank rises for most rivers. That said, a few rivers are running
at elevated levels from rains earlier this week, namely the North
River near Norwalk (NRWI4) and Des Moines River at Ottumwa (OTMI4).
Should these basins get hit with prolonged heavy rain tonight,
additional rises are certainly possible.

&&

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

&&

$$

SHORT TERM...Dodson
LONG TERM...Dodson
AVIATION...De Bruin
HYDROLOGY...Dodson