157
FXUS63 KDMX 210453
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1153 PM CDT Mon Jul 20 2026

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Strong to severe storms are forecast from this evening through
  the overnight. All severe hazards are possible before the
  convective complex exits Tuesday morning.

- Relief from the heat starts Tuesday and lasts through the work
  week before another warmup this weekend.

&&

.UPDATE...
Issued at 744 PM CDT Mon Jul 20 2026

The Heat Advisory has been expired but also did some tweaks to
the grids by incorporating the latest surface observations and
radar trends.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 226 PM CDT Mon Jul 20 2026

A classic July NW flow severe weather setup is in store for todays
enhanced risk across Iowa. A stacked 500mb trough and surface low is
currently approaching Lake Superior and the trailing cold front
through Minnesota to South Dakota will be our main storm initiation
mechanism today.

To the dismay of most of the recent CAMs, a few storms are already
forming along the cold front in southern Minnesota, though these are
elevated and the main show is likely to hold off until the boundary
layer continues to destabilize. Speaking of destabilizing, the heat
today is well underway as the grand finale of the past week of heat.
Between the expected highs in the mid 90s and dewpoints in the mid
70s, heat indices across a large part of the state are expected
to be between 100-110F. Many stations across central Iowa
already have an index over 100F, but mixing out of moisture may
keep them from surging too much higher. This will lead to a
large zone of 3500+ J/kg of CAPE across north central Iowa as
the cold front crosses the state. Hodographs are generally
supportive of supercells, particularly further east near the
warm front, with decent mid level shear and low level turning.
Around mid to late afternoon, early convection along the cold
front will have the best chance at briefly supercell mode,
capable of large hail and gusty winds. 3CAPE, 0-1 SRH, and
vorticity will all be most favorable for a tornado or two near
the warm front (likely in or near ARX`s CWA), though a powerful
updraft sitting on the cold front could be capable of producing
a tornado. The relatively large T/Td spreads and strong DCAPE
could transition the threat quickly to a more linear mode, and
damaging wind would then be the main threat. There is still
large uncertainty in storm coverage across the cold front this
afternoon. There is a scenario where initiation holds off until
mid evening, and another where elevated convection in MN
continues to intensify and establishes itself early as it
crosses into Iowa.

Storms into this evening and overnight will be dependent on how cold
pools are established this afternoon. Convection will likely
continue to develop this evening as the increasing LLJ overruns any
remnant cold pools and the cold front meanders over central Iowa. A
mainly damaging wind threat and perhaps large hail threat will be
associated with these storms through the evening and overnight.
Additionally, PWATs near 2" and some potential for training
thunderstorms would make for a higher flash flooding threat, though
this threat will be muted by the low soil moisture and mature crops.

Any remaining storms will likely clear out of southern Iowa by early
morning and give way to dry conditions on Tuesday. Relief from the
heat will finally arrive Tuesday with highs in the low to mid 80s.
Winds will stay quite breezy behind the cold front with gusts up to
30-35 mph in the afternoon. Additionally, the HRRR smoke guidance is
forecasting smoke to linger through the day tomorrow, even at the
surface, though it likely will be a bit improved from this morning.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 226 PM CDT Mon Jul 20 2026

More mild conditions are expected through the end of the work week
with highs in the upper 70s and 80s across the state. Continued
ridging out to our south and west will continue, but there is decent
signal for more shortwaves Wednesday into Thursday that could bring
in additional chances for showers and storms. Severe weather is less
likely with these storm chances, as moisture will be limited, but
more details will be sorted out in the coming days. The ridge is
again expected to intensify over the central plains during the
weekend and heat will likely return by Saturday and Sunday.
Continued NW flow could bring in a marginal chances for smoke
haze since wildfires are still ongoing in Canada.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1152 PM CDT Mon Jul 20 2026

Low chances remain for showers and storms near KOTM over the
next few hours, but most lingering activity will remain south of
the terminals into the morning, with dry conditions returning
before sunrise. Otherwise, the primary challenge will be
ceilings, as sub-MVFR ceilings at KDSM and KOTM are ongoing due
to low cloud debris overhead but should largely remain VFR.
There is a window for potential MVFR ceilings across the
northern terminals between 15-20z that looks to most likely
impact KMCW and KALO, before improving. Winds will becoming
northwesterly across the forecast area through the morning,
increasing by late morning through the afternoon with gusts up
to 20-25 knots.

&&

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

&&

$$

UPDATE...Vorst
SHORT TERM...De Bruin
LONG TERM...De Bruin
AVIATION...Bury