748
FXUS63 KDMX 052356
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
656 PM CDT Tue Aug 5 2025

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Thunderstorms possible late tonight into early Wednesday.
  Marginal Risk for primarily damaging winds. Storms will fester
  through Wednesday.

- Chance of storms again after midnight Wednesday night, highest
  confidence over northern Iowa at this time.

- Next best chance of storms Saturday night.

&&

.DISCUSSION...
Issued at 230 PM CDT Tue Aug 5 2025

A negatively-tilted trough was pivoting across Montana today,
slowing the ascent of the upper ridge in the southwest CONUS. A
portion of its energy will be left to move around the ridge later
today, bringing some synoptic support into play for showers and
storms late tonight. The better upper level jet support will remain
in the Dakotas, so the shear is weak in our area. An MCS is
forecasted to form tonight in South Dakota along the nose of the
LLJ. It will come with a damaging wind threat, highest early on
since it will be in the favorable wind environment mentioned above.
As the jet veers overnight, it will drop SSE into the instability
axis, coming across central Iowa through the morning. The line of
storms will become cold pool dominant upon entry into the state, so
any gusts will be weaker and sporadic, hence the Marginal Risk
of severe weather.

A trough from the PNW will replace the first one, again inhibiting
the ridge and opening up the region to a series of shortwaves into
the weekend. The next of which will arrive Thursday morning, this
time with the LLJ angled right into the state. PoPs right now are
concentrated over northern Iowa which is well placed due to
uncertainty with the EML further south. The moisture axis then
focuses on the main trough to the northwest, which will close off
and negatively tilt near the USA-Canada border. The upper-level jet
will round the trough axis in the Dakotas, increasing deep-layer
shear available. The cold front will tail off into Iowa by late
Saturday night, with a chance of thunderstorms (50%). This front
will then stall nearby into next week and remain a consistent
catalyst for convection for the region for much of next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 641 PM CDT Tue Aug 5 2025

VFR conditions ongoing and largely expected to continue through
the TAF period. Main aviation concern continuing to watch is
storm progression into the area Wednesday morning and beyond.
KFOD still looks like site with highest chances for morning
storms but confidence in timing/impacts remains lower so kept
with prob30 group. KDSM and maybe KMCW have next highest chances
for seeing storms/rain but activity should be decreasing through
Wednesday morning so confidence in extent of duration remains
too low for mentions at either of those sites at this time. Some
additional storm development later Wednesday remains possible
but would be dependent somewhat on morning activity. MVFR
impacts may accompany any showers/storms that do occur. Trends
will continue to be monitored closely with updates likely
tonight into early Wednesday. Lingering afternoon gusty winds
diminish tonight before increasing again daytime Wednesday.
Wind speeds will largely remain near to under 10-15 knots out
of the southeast to south with a few higher gusts outside of
storms. Any storms will have the potential to bring strong,
gusty winds.

&&

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

&&

$$

DISCUSSION...Jimenez
AVIATION...05