457
FXUS63 KDMX 291934
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
234 PM CDT Fri Aug 29 2025

.KEY MESSAGES...

- Isolated showers or storms this afternoon along and east of a Mason
  City to Ottumwa line and Saturday afternoon over western into
  northern Iowa. Lightning is the main hazard with a funnel
  cloud or wind gust to 30 mph from a dying shower or storm less
  likely.

- Patchy fog may develop over parts of northeastern into north
 central Iowa toward sunrise Sunday.

- 60-70% chance of showers and storms Sunday with these highest chances
  over western Iowa fading with eastward extent into central
  and eastern Iowa. Clouds, showers, or weak storms linger into
  Labor Day.

- Much cooler and drier air Wednesday through Friday.

&&

.DISCUSSION...
Issued at 234 PM CDT Fri Aug 29 2025

Upper air charts show that a longwave trough is over
southeastern Canada with a flattening ridge over the southern
Plains and central Rockies. In between these features, there is
fragmented, elongated shortwave energy from the northern Rockies
to just west of Iowa. The downstream trough has been and will
continue to slow down the eastward progression of this
fragmented energy. In addition, there is a residual surface
front from southeast Iowa/Burlington area up to east of Mason
City. Day Cloud Phase Distinction RGB shows this area as having
more vertically developed cumulus clouds. While most locations
will stay dry, this boundary has been the focus for widely
isolated showers and a few storms so far this afternoon over our
far northeastern and eastern service area into northeast and
eastern Iowa. While won`t rule out a funnel cloud in this weak
flow regime, the more favorable parameters look to set up over
northeastern Iowa. What showers or storms do form will likely be
of an airmass variety and may produce a wind gust up to around
30 mph. This is the result of dry air in the mid-levels and to a
lesser degree in the subcloud layer per forecast soundings.
Much of this activity will diminish after sunset.

Fog may once again form after midnight tonight over northeast into
north central Iowa, though mid and high level cloud cover may limit
the extent of this fog coverage. Any fog that does form will
dissipate shortly after sunrise. The stalled north to south boundary
once again will provide a focus for isolated showers or storms in
the afternoon and early evening hours with the focus this time over
northern Iowa with some into western Iowa as the fragmented energy
somewhat congeals into a closed mid-level low. No severe weather is
forecast , but lightning, the potential for a few funnel clouds, and
the potential of a few wind gusts from shower/storm collapse up to
around 30 mph would be possible.

The closed mid-level low will shift southeastward over Nebraska
Sunday into early next week. With the more focused energy and closer
proximity of this low, more coverage of showers and storms is
forecast on Sunday into Sunday night over western Iowa with chances
lessening into central and eastern Iowa. Again, not expecting severe
weather with the main hazard being just lightning on this day with
the additional cloud cover and moisture in the soundings mitigating
the funnel cloud and gusty wind potential that is found on Friday
and Saturday.

As this closed mid-level low begins to move away early next week,
cloud cover will linger along with showers or weak storms on Labor
Day. Confidence in timing and location of these on Labor Day is low
at this time. An upstream trough over central Canada will dive
southward sending a surface cold front through the state late
Tuesday into early Wednesday. Moisture along this front along with
synoptic lift should be sufficient for some degree of shower and
storm coverage as the front moves through. Behind the front, surface
high pressure will fill in over the Plains directing much cooler and
drier air on breezy winds into the region late in the week. Extreme
forecast index of high temperatures shows high ECMWF ensemble
support for unusually cool temperatures late next week. This is also
reflected in the NAEFS 500 mb height that show heights at the -0.5
percentile or lower. Dry conditions and high temperatures in the 60s
to low 70s will be common by late week with lows early Thursday
morning around 40 degrees over northern Iowa.


&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1242 PM CDT Fri Aug 29 2025

Scattered diurnal cumulus clouds have developed and they will
continue through mid-evening, but any CIGs will remain VFR.
There is just enough instability for isolated pop up showers,
maybe a thunderstorm through evening across central and eastern
Iowa. Coverage should remain <20%, thus left explicit mention
out of terminals for now, and will monitor for any short term
amendments. Winds today will remain light once again, generally
favoring a S/SW direction with values < 8 knots. Have re-
introduced fog for late tonight into early Saturday. Highest
confidence is at KMCW, where have added a few hours of IFR
conditions between 09z-12z for now. Less certain on fog at
KALO/KFOD, but included MVFR at KALO and just 6SM at KFOD as a
start.

&&

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

&&

$$

DISCUSSION...Ansorge
AVIATION...Fowle