442
FXUS63 KDMX 171927
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
227 PM CDT Fri Jul 17 2026

.KEY MESSAGES...

- Heat and humidity continues through the weekend. The multiple
  repeated days of heat through Monday with the potential for
  heat headlines.

- Low (20%) shower and thunderstorm chances through the rest of
  today and again tomorrow.


- Low (20%) shower and thunderstorm chances through the rest of
  today and again tomorrow.


&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 225 PM CDT Fri Jul 17 2026

Much like yesterday, this afternoon and evening will be warm and
humid with limited storm chances around the state. Radar shows a
small cluster near Ottumwa at the moment, which is in line with a
weak moisture plume being advected into southeastern Iowa. There is
very little forcing once again as a small vort max has passed the
area. Sounding profiles suggest convection today would be thermally
driven as a few locations reach their convective temperature.
Regardless, storm coverage is expected to remain low with a few
isolated cells around the state. CAPE and moisture are abundant
while shear is lacking, so this would lead to more popcorn
thunderstorms. Other things to note is that diurnal cumulus has once
again formed around the state, though coverage is much lower than in
previous days, signaling less saturation aloft. The diurnal cumulus
will dissipate after sunset.

The lack of cloud cover tonight once again leads to the potential
for fog overnight. For now, conditions look marginal. However, each
night before has looked just as marginal with shallow fog forming.
Other considerations for fog formation tonight would be dewpoints.
Even after adjustments, dewpoints have over performed in some spots.
Like previous forecasts, dewpoints have been poked up a degree or
two while temperatures were poked down.

Saturday, there are low possibilities for showers and thunderstorms
yet again. In a similar fashion to the past several days, storm
coverage is expected to be pretty limited. CAPE and moisture values
are expected to be plentiful again. The big difference with this is
more shear and the subtle boundary to provide forcing. Shear values
are approaching 30kts across the area. Model soundings show a strong
inverted-V which would be supportive of strong to marginally severe
wind gusts. Of note, there is some uncertainty with timing on the
boundary as it pushes south. A slower arrival of the boundary could
lead to increased storm chances farther north. For the time being,
most solutions are progging areas along and south of I-80 tomorrow
afternoon and evening. Outside of storms, heat remains as a focus
point. Warm overnight lows combined with our multiple days of high
temperatures near or above 90 and dewpoints in the upper 60s to low
70s could lead to heat headlines across parts of the area tomorrow.

Saturday night will be warm and humid again, with dewpoints hanging
out in the 60s and low temperatures in the high 60s to low 70s once
again. Lingering cloud cover and potential smoke in northeastern
could limit fog from developing Sunday morning, however this will be
much better assessed with guidance tomorrow.

Rounding out the weekend, Sunday will continue the trend of hot,
humid, and calm winds. As previous forecasts have alluded to, the
ridge which has been overhead will finally move, putting Iowa back
into southerly flow to begin the workweek.


&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 225 PM CDT Fri Jul 17 2026

The long-term forecast has much more uncertainty. For Monday,
deterministic models are hinting at more thunderstorm potential with
our biggest consideration being the location of the ridge. LREF
clusters now hint at Iowa being under the periphery of the
ridge, which would knock down the thunderstorm potential for at
least some of the state. The eastern extent of the ridge`s
influence will determine the axis of where any organized
convection would track. The most notable takeaways as far as
storm potential Monday is that the ingredients are in place and
better forcing will be available as we have a pattern change
taking place. As we transition to northwesterly flow, subtle
shortwaves will ripple overhead which will drive any
precipitation chances through the next week. LREF and
deterministic guidance show that the ridge will be well clear of
Iowa through midweek, which would lead to an increased area of
potential coverage for showers and thunderstorms as
opportunities arise. Finally, with this pattern chance,
temperatures are going to trend cooler. Instead of making daily
runs for the 90s, temperatures will be in the lower to mid 80s
at points through the week.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1204 PM CDT Fri Jul 17 2026

VFR conditions are expected to prevail this TAF period.
Relatively calm winds under 10kts are expected. This afternoon &
evening, there is a low (20%) chance for thunderstorms. After
dark, any storms that do form will diminish. Low confidence in
coverage and impacts over one terminal leads to no weather
mentions in the TAF. Otherwise, a light wind shift is expected
toward the end of this period as a weak boundary sags south
across Iowa.

&&

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

&&

$$

SHORT TERM...67
LONG TERM...67
AVIATION...67