129
FXUS63 KDMX 011040
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
540 AM CDT Tue Jul 1 2025

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Seasonable today, but turning warmer through Independence Day.

- While a few showers or storms near northwest Iowa and perhaps
  last into north central Iowa Wednesday morning (20% chance), a
  higher chance (30-40%) for scattered storms is forecast over
  northern and eastern Iowa late Wednesday afternoon into
  Wednesday night.

- Next highest chance (50-70%) for storms will be sometime between
  Friday night and Saturday evening with lower chances perhaps
  persisting into Sunday.

&&

.UPDATE...
Issued at 207 AM CDT Tue Jul 1 2025

GOES-East upper level water vapor imagery shows a trough axis
swinging through the state this morning. With plenty of subsidence
behind this feature, Nighttime Microphysics RGB is showing few if
any clouds over the state. That is expected to continue into today,
though we may see a few diurnal cumulus clouds develop toward and
into this afternoon. Forecast soundings do not show a lot of
moisture with the RAP/HRRR more pessimistic than the NAM/GFS on the
cumulus possibility. Highs today will be a few degrees higher than
yesterday with the 850mb temperatures changing little over the 24
hour period.

Into tonight, a subtle shortwave trough will top the ridge over the
Rockies and head into the Dakotas. As it does so and in concert with
a 40 knot, 850mb low level jet and some weak instability, showers
and thunderstorms are expected to develop around or after midnight
over the Dakotas per models and HREF paintballs. This cluster of
storms is expected to ride down towards Iowa Wednesday morning
reaching northwestern Iowa around sunrise and are expected to be
weakening as they move into the state with weaker effective shear.
We may see a few showers with rumbles of thunder fester over
northern Iowa through the day, but overall expecting much of the
daytime hours to be dry. Late in the afternoon into Wednesday night,
another weak shortwave trough drops down the ridge into Iowa. This
may kick off a few storms toward or around sunset, but more
scattered storm development is expected into the night as a 30 knot,
925mb low level jet develops and points into Iowa. Instability is
modest around 500 J/kg and while hodographs are linear and point to
some degree of hail concern, effective shear is weak for storm
organization around 20 knots or so. Storm motions to the southeast
are slow around 15 to 20 knots and in a favorable efficient warm
rainfall process environment plus top soils at the 80th percentile
of soil moisture over northern Iowa. Outside of the lone FV3 QPF,
flash flooding is not a concern at this time. This activity will
weaken and push off to the east as we head into the day
Thursday.

&&

.DISCUSSION...
Issued at 250 PM CDT Mon Jun 30 2025

Morning objective analysis highlighted the shortwave trough
over the region, this being the culprit for the shower and
storms in the north this afternoon. Instability in the north
being generated by the steepening lapse rates from the cooling
profile. The bulk of the instability has been squashed south of
the state due to the MCS this morning, but some will hold across
southeast Iowa this afternoon and evening, hence the marginal
threat for wind. Storm mode within the Marginal Risk will be
disorganized clusters, updraft columns that will collapse on
themselves. Inverted-V soundings will allow for strong cold
pools during the storm decaying cycle mentioned above,
contributing to the severe wind threat. Nonsevere gusty winds
will also be possible with showers in the north. The wind threat
statewide will diminish after sunset. PoPs have been kept low
as models have generally been too robust on precipitation
coverage through this morning and early afternoon.

High pressure follows the CAA regime and holds highs in the 80s for
another day. Its upper air reflection in the form of a ridge will be
building over the High Plains, keeping us in northwest flow for the
next several days. We`ll get a mixture of warming and synoptic
forcing in this regime, along with moisture return inching its way
in along the LLJ axis. An instability axis exceeding 2,000 J/kg
MUCAPE sets up in northwest Iowa, forming a N-S gradient somewhere
through central Iowa. An MCS will form along the LLJ nose, slowly
progressing southeastward through the night. It will initially
have an EBWD of ~30kts to work with, meaning there could be an
early window of severe storms. The instability axis itself
serves as another point of convergence, meaning some scattered
storms with some hail potential may form. The MCS will drop
south and east through the night as the jet veers, but will
encounter the apex of a ridge, a region of weak flow, causing
storm motions to slow down. If this setup played out, there will
be a narrow region of heavy rainfall in northern Iowa that will
last much of Wednesday night. The instability axis won`t move
far for Thursday evening and may offer another chance at storms
at peak heating.

The upper-level ridge centers over the state by Friday and will be
followed by another shortwave trough for the holiday weekend. The
first round of associated precipitation will be on Friday evening.
The synoptic evolution differs in deterministic runs at this point
in time, but would expect mesoscale features that fall out of prior
convection to add another facet to the kinematics available for the
warm, moist, and weakly capped summertime airmass all weekend. The
NBM PoPs are high, but have the right idea for spatial coverage in
the afternoon beneath the main instability axis.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 540 AM CDT Tue Jul 1 2025

VFR conditions will prevail through the period at all terminals
with high confidence. FEW to SCT diurnal cumulus clouds will
develop this afternoon dissipating shortly after sunset. Breezes
from the northwest will be common during the daylight hours, but
will become from the southwest this evening.

&&

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

&&

$$

UPDATE...Ansorge
DISCUSSION...Jimenez
AVIATION...Ansorge