Severe Thunderstorm Warning 289, NWS Des Moines, IA

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

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

.KEY MESSAGES...

- A Heat Advisory is in effect through later this evening with
  heat indices from 100-110F expected.

- Strong to severe storms are forecast from this afternoon
  through the overnight, beginning in northern Iowa and making
  it to southern Iowa by early Tuesday morning. All severe
  hazards are possible.

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

&&

.UPDATE...
Issued at 522 PM CDT Mon Jul 20 2026

Showers and storms have caused temperatures to fall under Heat
Advisory criteria; therefore, have canceled a portion of Heat
Advisory where convection moved through. Also, incorporated the
latest surface observations and radar trends.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
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 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 /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 626 PM CDT Mon Jul 20 2026

VFR TAFs are present with this issuance for the 5 TAF sites;
however, over the next few hours, a strong convective complex
will continue to dive south impacting KDSM and KOTM before
exiting the area by 09Z. Terminals KFOD, KMCW and KALO will
remain dry through the rest of the period. Strong northwesterly
winds are expected to develop after 13Z and persist through the
remainder of the period. Wind gusts will approach 25 to 30
knots. KMCW and KALO could see increasing and lowering CIGS
between 13Z and 19Z as the surface's low backside low clouds
move across northeastern Iowa.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT this evening for IAZ044>050-
057>062-070>075-081>086-092>097.

&&

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

Hazardous Weather Outlook
National Weather Service Des Moines IA
238 PM CDT Mon Jul 20 2026

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-211945-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun-
Webster-Hamilton-Hardin-Grundy-Black Hawk-Crawford-Carroll-Greene-
Boone-Story-Marshall-Tama-Audubon-Guthrie-Dallas-Polk-Jasper-
Poweshiek-Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union-
Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-
Appanoose-Davis-
238 PM CDT Mon Jul 20 2026

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This afternoon and tonight

A Heat Advisory is in effect for the area today. Please refer to
the National Weather Service website at weather.gov/desmoines for
further details.

Strong to severe thunderstorms are possible this afternoon into
tonight with an Enhanced Risk (level 3 of 5) for severe storms.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Additional thunderstorms are possible Wednesday night into
Thursday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed today.

67

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