Johnston, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

586
FXUS63 KDMX 232325
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
625 PM CDT Tue Jun 23 2026

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

.KEY MESSAGES...

- A few showers and storms are expected tonight and Wednesday.
  The severe weather threat is low.

- Storms possible Saturday night and early Sunday followed but
  much warmer and more humid conditions for early next week.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 207 PM CDT Tue Jun 23 2026

Another afternoon of widespread cumulus development across Iowa.
Increasing southerly flow over western Iowa has allowed dew points
to increase into the low 60s, though diurnal mixing has led to these
lowering a bit early this afternoon. That does somewhat reflect the
lack of deep layer moisture currently over the state and that is any
convective initiation at this time. Similar to Monday, there are
some areas that have more vertical extent occurring, in particular
east central Iowa with hints this will arc north/northwest towards
the Waterloo and perhaps Mason City areas. This region will also
have a region of 0-3 km CAPE developing along a gradually northeast
lifting boundary. Also similar to yesterday, with the weak boundary
and the vertical stretching component of the 0-3 km CAPE, there
remains a low chance for a funnel or two, though that potential may
be northeast of the forecast area soon. Overall, shower and a few
non-severe thunderstorms are expected tonight as modest short wave
energy moves over a region of low static stability. An upper closed
low will be over northern Minnesota on Wednesday morning. This upper
low will rotate a vorticity lobe into northeast Iowa, which could
spark a few thunderstorms. In addition, A few storms may fire along
a boundary that will be passing through the state with the focus
over the southeast.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Issued at 207 PM CDT Tue Jun 23 2026

Zonal/westerly flow aloft will be in place Thursday and Friday.
Still monitoring the evolution of building lower Mississippi Valley
sub-tropical high and and upper low descending into the western
CONUS. This will lead to a strong push of warm advection across Iowa
as a steepening southwest flow develops. This may bring a few
thunderstorms to the state followed by heat and humidity for Sunday
and into early next week. Heat index values could approach 105
degrees in some areas. At some point, the evolution of the western
trough relaxing and the sub-tropical high nudging north, may lead to
the ring of fire MCS complexes rolling along the northern periphery
of the sub-tropical high and potentially impacting Iowa.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 625 PM CDT Tue Jun 23 2026

VFR conditions will prevail for much of the TAF period. However,
widely scattered SHRA/TSRA will move through the area overnight
and may produce periodic MVFR ceilings and reduced visibilities.
These are most probable at the northern terminals (MCW/ALO/FOD),
where longer PROB30 groups are carried along with a TEMPO at
MCW. Farther south, the probability of impact is lower thus only
a short PROB30 group is carried at DSM with no mention at OTM.
Amendments may be needed overnight based on short-term radar
trends. VFR conditions will then return behind the SHRA/TSRA on
Wednesday.

&&

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

&&

$$

SHORT TERM...Donavon
LONG TERM...Donavon
AVIATION...Lee