523
FXUS63 KDMX 151116
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
616 AM CDT Wed Jul 15 2026

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

.KEY MESSAGES...

- Hot and humid conditions will persist through this weekend.
  The heat index will peak in the upper 90s to near 100 degrees
  each day.

- Isolated thunderstorm chances return on Thursday and Friday.
  The threat of severe weather is low.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 104 AM CDT Wed Jul 15 2026

Iowa will remain smothered beneath a deep-layer ridge for the
next several days. The result will be persistent heat and
humidity, and little has changed in forecast thinking in that
regard. Only slight adjustments to temperatures and dewpoints
have been made, and heat index values will still peak around the
upper 90s both today and Thursday. Meanwhile, we are once again
seeing patchy fog develop early this morning due to the
combination of high surface dewpoints, calm winds, and clear
skies. Some high-res guidance suggests the best dense fog
chances will reside in our northern and western counties around
sunrise this morning, with somewhat higher coverage than Tuesday
morning. However, with an expectation that any visibilities
below 1/4SM will be spotty and transient, no advisory has been
issued at this time. Observations will be closely monitored
through sunrise.

One feature of note is a slight weakness in the 500 MB ridge,
lying to the south of the surface ridge over AR/MS/TN at this
time. There are slight ripples of enhanced 500 MB vorticity in
this area, along with deeper moisture content, resulting in
greater cloud cover and some showers and thunderstorms. Forecast
models are unanimous in drifting this feature northward into
Missouri later today and tonight, then to some extent into Iowa
on Thursday. However, it will be weakening during this time and
a reorientation of the 500 MB ridge will also cause it to turn
more northeastward. The result is that any impacts in Iowa will
most likely be confined to about the southeastern half or so of
the state, where isolated to scattered thunderstorms may occur
Thursday and Friday before the area shifts away to our east.
Have thus kept POPs low on Thursday, but expanded their coverage
a bit to indicate slight (20%) thunderstorm chances in our
central, southern, and eastern counties during the afternoon and
evening hours. Given the complete lack of flow/shear and weak
forcing, it is anticipated any convection that does occur will
be in the form of "airmass" or "popcorn" storms with a low
threat of any severe weather.

Finally, widespread smoke from wild fires in Canada has been
advecting east southeastward over Lake Superior, around the
northern periphery of the 500 MB ridge that stretches from the
Midwestern U.S. down into the Ohio River valley and Appalachian
Mountains. As the ridge becomes somewhat pinched off in the next
few days but doesn`t really shift much southward it appears the
smoke will make some inroads and sink over Michigan, Wisconsin,
and parts of Minnesota by tonight and Thursday. However,
indications are that it should remain northeast of our area
through Thursday.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 250 PM CDT Tue Jul 14 2026

The upper level pattern begins to transition through the second half
of this week and through the weekend, as a long-wave trough digs in
over the northeastern CONUS. The upper ridge overhead will begin to
modify and translate back westward as this occurs, but still
generally remains overhead through the end of the week. The result
will be continued warm temperatures, but slight changes to the low
level moisture and flow patterns. First, we`ll see the surface high
pressure begin to weaken and low-level flow become more south to
southwesterly. This will bring warmer 850 mb temperatures from the
plains eastward into Iowa, leading to warmer surface temperatures.
The warmest day looks to be Friday, as highs climb into the mid to
upper 90s with widespread heat indices near or exceeding 100F. As
mentioned previously, depending on how heat indices play out
Wednesday and Thursday, heat headlines may be needed later in the
week as we see multiple days of near or above 100F heat indices
Friday and into the weekend.

The more south to southwesterly flow will also allow for more low to
mid-level moisture to be transported back into the area. With the
better layer moisture and less subsidence from the high pressure,
the potential for diurnally driven showers/storms returns later
Thursday and again on Friday, primarily over southern and eastern
Iowa. Instability will be plentiful, as is typically the case this
time of year, but shear will be very low due to the weak flow
through the layer. Therefore, any storms will be just general,
pulsey thunderstorms with a low severe risk. Our ridge continues to
push westward into the weekend, bringing us more into a northwest
flow pattern. Shortwaves passing through this pattern will bring
additional precipitation chances to end the weekend and into early
next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 615 AM CDT Wed Jul 15 2026

Patchy fog has formed once again early this morning, but will
dissipate by 12Z or very shortly thereafter. It may occur again
Thursday morning, but again will be patchy and transient, with
confidence in occurrence at any given location and time too low
to include in the TAFs at this range. Aside from fog
considerations, no aviation impacts are anticipated with nearly
clear skies and very light winds.

&&

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

&&

$$

SHORT TERM...Lee
LONG TERM...Dodson
AVIATION...Lee