595
FXUS63 KDMX 070922
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
422 AM CDT Mon Jul 7 2025

.KEY MESSAGES...

- A few thunderstorms for central and southwest Iowa possible
  today. More widespread storms tonight with a few strong storms
  possible with damaging wind gusts.

- Additional storm chances Tuesday with the severe weather
  threat low. More widespread storm chances by Thursday night
  and Friday.

&&

.UPDATE...
Issued at 420 AM CDT Mon Jul 7 2025

High pressure ridge is over Iowa early this morning and with the
light winds and mostly clear skies, radiational cooling is ongoing.
That said, surface dew points in the 60s to near 70 are ensuring
that temperatures do not drop too far. Some fog has developed mainly
in the river valley regions and most expansive over far southeast
Iowa. The PV 1.5 pressure surface anomaly that was over southern
California 24 hrs ago, is now over northeast Colorado and west
central Nebraska. An MCS did develop ahead of the system it dove
southeast along the instability axis. This is an area the CAMs have
performed poorly this convective season is a too far east bias on
storms. The MCS dropping through western Kansas has followed the
instability and the Corfidi Vectors and not the 850-300 mb mean
stearing flow. Additional weak convection has developed in central
Nebraska near a theta-e advection max and near the edge of the low
level jet.

Convective trends today are a challenge as chances today will hinge
on the arrival of the PV anomaly and the strength of the elevated
mixed layer capping over central and southern Iowa. Expect some
convective bubbling in that part of the state but there will be a
lack of any moderate or better dynamic while the surface high
pressure ridge lingers into this afternoon. That ridge is relatively
deep with little to no flow below 700 mb. The stronger forcing
arrives this evening and overnight as a stronger upper level short
wave and surface boundary reach the state. This will lead to
increasing storms and a potential line moving from northwest to
southeast. The most widespread area will be central and southwest
Iowa. A few strong storms with damaging wind gusts are possible.
That is a broken record for severe weather threat for central Iowa
this convective season with little to no deep layer shear present.

Shower and thunderstorm chances will persist on Tuesday as a ribbon
of deeper layer moisture remains. That deeper moisture will limit
instability and lapse rates therefore the potential for any severe
weather is low. High pressure ridging will arrive by Wednesday
afternoon into much of daytime Thursday. Additional storm chances
arrive late week, in particular Thursday night and Friday as
stronger short wave energy arrives.

&&

.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.

&&

$$

UPDATE...Donavon
DISCUSSION...Hagenhoff
AVIATION...05