324
FXUS63 KDMX 070401
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1101 PM CDT Sun Jul 6 2025

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

.KEY MESSAGES...

- Thunderstorms reach western Iowa on Monday morning with more
  widespread thunderstorms in the evening and into Tuesday. A
  few stronger storms are possible, however the overall severe
  threat is low.

- Additional chances for thunderstorms by Thursday and through
  the end of the week into next weekend.

&&

.DISCUSSION...
Issued at 224 PM CDT Sun Jul 6 2025

Lingering fog this morning diminished quickly with sunrise but
moisture has lingered over the area. This afternoon dewpoints have
been in the upper 60s to mid 70s across the area, something pretty
evident if you step outside today. With plenty of moisture around,
low cumulus has bloomed across the area. Conditions are pretty
unstable out there with only a weak boundary out across far eastern
Iowa. CAMs have picked up on this and most develop spotty convection
late this afternoon and evening for our neighbors over in the Quad
Cities CWA. Closer to home there is little forcing of note, but with
so much instability to work with, subtle small scale features could
result in a very isolated shower or t-storm popping in southern Iowa
today.

An overnight MCS across Nebraska is then expected to reach far
western Iowa Monday morning, moving across central Iowa into the
afternoon. As instability increases into the afternoon with
1500+ J/KG of available MLCAPE, expect some restrengthening of
the storms with this wave, even though shear remains quite low.
Later convection across South Dakota is expected to have grown
upscale into an MCS, approaching northwest Iowa by evening.
Again, 0-6 km shear remains low, under 20 kts in most cases, so
storms will struggle to organize, but the MCS is expected to
ride the instability gradient into Iowa through the overnight.
The question is where this gradient and any remnant outflows
from earlier convection set up. There is also indication that
afternoon convection in Nebraska will grow upscale and into Iowa
in the evening, but CAMs continue to struggle with little flow
available. Some, like the NAM nest and ARW , attempt to combine
the SD and NE convection into a larger line across the area late
Monday night and thorugh Tuesday while the HRRR favors keeping
the activity separate. Others like the RAP and Fv3 favor a
scenario where earlier convection delays and weakens the
overnight convection. While the evolution is uncertain, the lack
of shear available to help organize storms should mitigate most
of the severe risk. A few stronger storms are possible, along
with pockets of heavier rain with PWATs over 2" and deep warm
cloud depths for efficient rain production.

High pressure provide a reprieve mid week, but by Thursday and into
the weekend an approaching more robust shortwave passes across the
area. The better forcing, for now, appears to be concentrated north
of the area. We`ll have to watch how this evolves later this week as
available AI and ML data indicates some severe potential into the
area. As continues to be the case, efficient rain production
looks likely regardless of severe potential with PWATs exceeding
2 inches.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1057 PM CDT Sun Jul 6 2025

Although VFR conditions ongoing and largely expected to continue
during much of the TAF period, watching the potential for
developing fog again overnight, especially near eastern sites
KMCW, KALO, and KOTM. Confidence in extent of impacts remains
lower as typical with patchy fog development, but started with
some fog mentions into MVFR or even IFR visibilities though
adjustments are likely as fog begins to develop. Additionally,
showers/storms are forecast at times on Monday, especially later
in the day into the evening, but confidence in timing or
location has not increased enough with this package to include
any precipitation mentions at this time and will be addressed in
future issuances. Winds remain light and variable overnight and
through much of Monday.

&&

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

&&

$$

DISCUSSION...Hagenhoff
AVIATION...05