624
FXUS63 KDMX 012249
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
549 PM CDT Tue Jul 1 2025

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

.KEY MESSAGES...

- Quiet this afternoon and evening, then chances for some
  residual showers and storms dropping southeastward into
  northwest Iowa early tomorrow morning. Gusty winds are
  possible northwest.

- Additional shower and thunderstorm development is possible
  through Wednesday afternoon and evening. Conditional severe
  threat in northwest Iowa, dependent on how convection plays
  out.

- Warm through the rest of the week, shower and storm chances
  return on Friday into the weekend.

&&

.DISCUSSION...
Issued at 250 PM CDT Tue Jul 1 2025

A look out the window in central Iowa shows a quiet and pleasant day
with mostly clear skies overhead. Cumulus clouds have begun to pop
up early this afternoon, thanks to a thin layer of instability and
saturation around 5000 to 6000 ft. Temperatures are warm but
seasonal in the upper 70s to low 80s with light winds out of the
west to northwest. This same picture can be found throughout the
state today as surface high pressure sits overhead; a much needed
breather to what`s been an active couple of weeks in Iowa.
Unfortunately, this moment of serenity is short-lived as shower and
thunderstorm chances return to the forecast tonight into tomorrow,
then yet again through the holiday weekend.

The 500 mb flow pattern shows generally northwest flow overhead,
which will see a weak shortwave traverse through it tonight into
tomorrow. This wave will pull warm, moist air to our west and
southwest up towards the state, as well as provide weak forcing for
shower and storm chances over the Dakotas tonight. Convection
tonight over the Dakotas will first develop along a 35 to 40 kt LLJ
oscillating southeastward with the shortwave. Short-range models
show this activity being mostly multi-cellular, but some do suggest
upscale growth into at least a weak MCS. This MCS then rides
southeastward along the instability gradient, fueled by the LLJ. The
CAPE/shear environment is meager once this complex arrives in Iowa,
which will help to mitigate severe weather concerns by the time it
arrives around daybreak. HRRR deterministic output does imply
at least some sub-severe wind gusts over northwest Iowa with
storms tomorrow morning, but these generally diminish before
reaching the northwest portions of our forecast area. This is
echoed by HREF max wind gust output which also peters out as
storms arrive in the less favorable severe environment in
central Iowa tomorrow morning. Given the less favorable
environment in central Iowa and support from both ensemble and
deterministic output, severe weather appears unlikely at this
time.

As is typical for these weakly forced systems, these morning storms
will dictate how convection the rest of the day plays out. In the
event that a cold pool/MCS progresses southeast into the state, a
residual boundary could set up and provide lift for parcels in an
increasingly unstable environment tomorrow. In this scenario, storms
would fester along the boundary as the warm, moist west
southwesterly flow collides with it throughout the day. This becomes
especially true during peak heating in the late afternoon and as a
relatively weak LLJ ramps up in the evening. With 2000-3000 J/kg of
instability in northwest Iowa tomorrow afternoon, roughly 30 to 40
kts of deep layer shear overhead, and a well mixed boundary layer
(DCAPE of 500-1000 J/kg), any surface based storms could become
organized and produce strong winds and hail. That said, model
soundings show an elevated warm layer working to negate storm
development within this better afternoon environment. Will want to
watch how mixing impacts this tomorrow, as surface based convection
would lead to our greatest chances for severe weather, especially in
northwest Iowa. Into the evening, instability begins to diminish but
a 20 to 30 kt LLJ will help provide lift for sub-severe storms into
the evening and overnight. Moderate to heavy rainfall will be
possible with any stronger storms as well, and training convection
along a boundary could lead to isolated pockets of heavier rainfall
amounts. Of course, this is all contingent on a boundary, or other
lifting mechanism, being present in the otherwise neutral
environment. While the HRRR/RAP are generally reliable, other
convection allowing models aren`t nearly as aggressive with storms
tomorrow, some of which remain almost entirely dry through Wednesday
night. Therefore, while there is a potential for isolated
strong to severe storms, the threat is certainly conditional and
dependent on how mesoscale features evolve.

Our northwest flow regime generally persists into Thursday, but will
steadily drift eastward as troughing builds over the western CONUS
As this occurs, the thermal ridge will build into the state,
bringing warmer temperatures in the upper 80s and 90s through the
second half of the week and into the first part of the holiday
weekend. A brief period of upper ridging will be in place overhead
Thursday night into Friday morning, providing at least a short
period of dry weather on Fourth of July morning. Unfortunately, as
we go later into the day Friday, the mid-level trough will begin to
knock on the doorstep, which could bring shower and thunderstorm
chances to the western half of the state as soon as Friday
afternoon, with chances persisting along a trailing cold front
Friday evening and through the day Saturday. While it`s a bit far
out to be ironing out any specific details regarding severe weather,
there will be plenty of instability present to produce storms Friday
through Saturday, although initial indications show shear may be
lacking for widespread severe weather. Regardless of severity,
lightning poses a risk to outdoor plans on the busiest summer
holiday of the year, so will be watching convective trends this
weekend closely.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 547 PM CDT Tue Jul 1 2025

VFR conditions will occur tonight into Wednesday morning. The
wind will diminish and will be light from the south/southwest
for much of the night. The wind will remain mostly below 12 kts
on Wednesday though a few locations may briefly top that at
times. Shower and thunderstorms chances will increase over
northern Iowa by mid to late afternoon. Have included a Prob30
group only at KMCW, where the most confidence exist through this
forecast period.

&&

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

&&

$$

DISCUSSION...Dodson
AVIATION...Donavon