867
FXUS63 KDMX 021956
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
256 PM CDT Wed Jul 2 2025

.KEY MESSAGES...

- Low chances (less than 50%) for scattered showers and storms
  this afternoon through the overnight. A strong storm or two
  are possible, with hail being the main concern.

- Hot and humid tomorrow with isolated showers/storms possible
  in northwest Iowa in the afternoon and evening.

- Shower and thunderstorm chances move in from west to east
  Friday through Saturday. Severe weather threat looks low, but
  will be better determined in the coming days.

&&

.DISCUSSION...
Issued at 250 PM CDT Wed Jul 2 2025

A remnant MCV over southern/southwestern Iowa continues to produce
isolated thunder and showers early this afternoon. While this
complex is moving into a less favorable environment in central
Iowa, boundary layer mixing will lead to destabilization through
the afternoon which may lead to additional showers/storms in
proximity to the MCV. Of course, short range models provide
little confidence to this afternoons forecast, as they`ve been
trying to dissipate this precipitation for the last couple of
hours. Therefore, will be keeping a close eye on radar trends as
this MCV continues to churn this afternoon. With more mixing in
the boundary layer, storms that develop in proximity to the MCV
could become surface based, which would provide a slightly
better shear profile thanks to the southwesterly low level
winds. SPC mesoanalysis data reflects this, with effective shear
values ahead of the MCV around 20 to 30 kts and modest but
increasing SBCAPE values of 500 to 1000 J/kg. This would be
conducive for a few stronger storms, especially further west
toward the higher instability. Fortunately, the MCV should
continue eastward away from the more favorable severe weather
environment to the north and west. This area will have
instability values in excess of 2000 J/kg and a much better
shear environment boasting 35 to 40 kts of effective shear, as
well as long hodographs aloft. This makes this region more
favorable for severe thunderstorms capable of producing large
hail. Despite this favorable environment, this area also looks
capped off with -50 to - 100 J/kg of mixed layer convective
inhibition (MLCIN) thanks to the warm layer aloft. With no
boundaries/convergence nearby, parcels will struggle to find any
source of lift to displace parcels and bypass this convective
inhibition. Therefore, there is a conditional threat for an
isolated severe storm or two in the north and west, but the
likelihood of producing one in this environment is low.

Models continue to struggle with resolving how convection will play
out in the overnight hours, as solutions vary on the strength of the
low level jet (LLJ). The HRRR and RAP have been in lockstep today,
struggling to generate any precipitation overnight tonight.
Conversely, more rambunctious models like the NAM Nest and FV3 show
storms developing along the nose of the low level jet through much
of the overnight hours. The GFS also indicates a slightly stronger
LLJ and convection overnight, in contrast to it`s higher resolution
siblings (HRRR/RAP), although it has backed off on the amount of
precipitation with it`s 18z run. This all to say, tonights
shower and thunderstorm chances are not a high confidence
scenario. Most unstable CAPE will remain in the 1000 to 2000+
J/kg range overnight, but the deep layer shear environment will
be waning as the surface decouples. This will help negate the
threat for organized storms/severe weather, but the higher
instability does still leave a concern for at least pulsey
convection and hail overnight. Moderate to heavy rainfall would
also be a concern if precipitation matches what is shown in the
NAM Nest/FV3, but this looks to be on the higher end of our
expectations at this time.

The low end chances for scattered showers and storms continues into
Thursday, but do drift farther northeast as the upper level
northwest flow regime continues further east and upper ridging
builds from the west. With a very similar environment to today,
and the same lack of real great forcing, expecting a similar
low end thunderstorm threat in the far northwest portions of the
forecast area on Thursday afternoon and evening. Shear will be
slightly weaker on Thursday, but there will also be less of a
warm layer to inhibit storms, producing less of a severe weather
threat but more opportunity for storms to develop. That said,
have kept precipitation chances lower given the potential for
storms to be displaced from our area entirely, depending on the
model you choose.

In addition to the scattered storm chances in the afternoon,
temperatures will be much warmer tomorrow with highs in the upper
80s to low 90s. With dewpoints in the low 70s, heat indices will
push into the upper 90s to near 100 in some locations, making for a
muggy day in Iowa. Temperatures then stay warm into the Fourth
of July holiday, but increasing cloud cover ahead of the
approaching upper level trough will drop temperatures down
slightly in the west. This cloud cover will precede the return
of shower and thunderstorm chances through the holiday weekend,
beginning in the west on Friday and persisting area-wide through
Friday night into Saturday. The severe weather threat will
continue to be assessed through the coming days, but the general
lack of shear being depicted in longer range models will make
it difficult for strong, organized storms to develop. Forecasted
PWATs over 2" and strong low- to mid- level moisture transport
suggests storms could be efficient rainers, which could lead to
aggravation on area rivers. However, forecast QPF isn`t overly
high at this range, so will continue to monitor this threat as
we draw closer and models begin to resolve things better.
Regardless, the most important takeaway is the potential for
thunderstorms/lightning during a busy holiday weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1234 PM CDT Wed Jul 2 2025

Remnants of overnight storms in Nebraska are drifting through
southern Iowa today, leading to broken to overcast skies near
KDSM and potentially KOTM this afternoon. No rain or lightning
is anticipated for either site at this time, but will be
monitoring for any redevelopment through the afternoon and
evening. Winds are light out of the southwest today, then become
more southerly this evening and overnight. Have maintained
PROB30 groups for isolated to scattered showers/storms overnight
into Thursday morning at KFOD, KMCW and KALO, but confidence in
these impacting any given site. Also removed thunder mention
with confidence decreasing in lightning impacts at terminals.

&&

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

&&

$$

DISCUSSION...Dodson
AVIATION...Dodson