Flash Flood Warning 30, NWS Quad Cities, IA

Area Forecast Discussion
National Weather Service Quad Cities IA IL
627 AM CDT Mon Jul 20 2026

.KEY MESSAGES...

- Strong to severe storms are expected today and tonight with a
  morning round followed by a late afternoon/overnight round.
  The Storm Prediction Center has an enhanced, level 3 out 5,
  risk for severe storms along/north of I-80. South of I-80 a
  slight, level 2 out of 5, risk for severe storms exist.

- Humid conditions will be seen across the area today with parts
  of the area seeing peak heat indices of 95 to 100. A heat
  advisory remains in effect for areas to the west and southwest
  of the Quad Cities for peak heat indices up to 105 degrees.

- Smoke from Canadian wildfires keep hazy skies and poor air
  quality through tonight. The hazy skies may or may not persist
  past tonight.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 241 AM CDT Mon Jul 20 2026

The first of two rounds of storms will arrive by 9 AM, possibly an
hour earlier, in the form of a decaying storm complex. The very
short term models indicate most of these storms should be sub-severe
with brief downpours and winds gusting up to 35 mph. HOWEVER, a
rogue severe storm cannot be ruled out with the energy potential in
the atmosphere.

The somewhat good news is that the morning round of storms will help
suppress temperatures and dew points which will keep heat indices in
the 95 to 100 range outside of the current heat advisory.

Areas that do not see any rain this morning will turn hot and humid
by mid-day. The current temporal/areal coverage of the heat
headlines looks good. We will SPS the remainder of the area for heat
indices of 95-100 with a mention that some areas adjacent to the
heat headlines may see heat indices exceed 100 for a couple of hours.

Boundaries left over from the morning convection will combine with
diurnal heating to provide areas for new convection mid to late
afternoon. The strengthening winds aloft combined with the arrival
of the cold front will allow the initial discrete cells to quickly
grow upscale into one or two bowing line segments.

During the discrete storm cell phase, all severe modes will be
possible. Once the individual storms grow upscale into bowing lines,
damaging winds, potentially 75+ mph, become the primary risk with
brief spin-up tornadoes a secondary risk.

Peak areal coverage of storms should occur between 4 PM and 1 AM
with a slow decrease the remainder of the night.

After 1 AM storms will slowly decay as the cold front pushes them
south of the area. Isolated strong to severe storms will still be
possible.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 241 AM CDT Mon Jul 20 2026

Tuesday through Thursday...some lingering early morning showers or
storms are possible in the far south as the cold front moves into
southern Missouri. Humid conditions will be seen Tuesday until a
secondary front moves through. Once this front moves through much
less humid conditions and cooler temperatures will be seen Wednesday
and Thursday.

Thursday night/Friday
Assessment...low (<25%) confidence on rain chances

The model consensus is narrowing the time frame for rain to late
Thursday night into Friday morning. Rain chances have increased
slightly (20-35%) mainly south of I-80 but this appears to be an
anomaly tied to one specific model.

The weak low and associated fronts are progged to be across Missouri
so the better rain chances will be associated with the higher
moisture and stronger forcing. Indeed, a dprog/Dt of the various
models shows a southward shift to the moisture/wind convergence;
closer to the frontal boundary. This adds support that the uptick in
rain chances is an anomaly. I suspect rain chances will slowly
decrease as the week progresses.

Friday night through Sunday
Assessment...a certainty (>98%) of slowly rising humidity levels

All models show southerly flow redeveloping over next weekend as the
heat dome builds north in the Plains. Dew points in the 50s Friday
night will slowly climb into the low to mid 60s Saturday with mid to
upper 60s dew points by Sunday. The increasing temperatures and
moisture will slowly push heat indices into the 90s by Sunday.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 623 AM CDT Mon Jul 20 2026

MVFR visibilities from wildfire smoke will continue through at
least 18z/20 across eastern Iowa and northern Illinois. A
convective complex will arrive after 12z that may produce brief
periods of IFR conditions. Boundaries from this complex
combined with daytime heating and the approaching cold front
will aid in developing convection after 20z/20 that is expected
to rapidly grow into lines that impact eastern Iowa and northern
Illinois through 06z/21 and potentially 12z/21. Thunderstorms
this evening will be very strong, with LIFR brief visibilities
with rain and hail, and gusty winds over 40kt. Some storms may
be able to push 60kt winds this evening.

Overnight, dry air will arriving behind a cold front, with
northwest winds and mainly VFR visibilities.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Heat Advisory from noon today to 8 PM CDT this evening for
     IAZ051-063-076>078-087>089-098-099.
IL...Heat Advisory from noon today to 8 PM CDT this evening for
     ILZ025-034.
     Air Quality Alert until midnight CDT tonight for ILZ001-002-
     007-009-015>018-024>026-034-035.
MO...Heat Advisory from noon today to 8 PM CDT this evening for
     MOZ009-010.

&&

SHORT TERM...08
LONG TERM...08
AVIATION...Ervin

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