River Flood Warning 14, NWS Quad Cities, IA

Area Forecast Discussion
National Weather Service Quad Cities IA IL
710 PM CDT Tue Jul 29 2025

.KEY MESSAGES...

- Heat indices will range from 95 to 105 for areas along/south
  of I-80 this afternoon and evening. Heat Advisory remains in
  effect for these areas.

- Low potential (20-30%) of a scattered thunderstorm this
  afternoon and evening. Much higher chances (70-90%) of a round
  of thunderstorms late tonight through Wednesday. Some storms
  may be severe with damaging winds the main hazard.

- Rainfall amounts tonight through Wednesday night could be in
  the 1-2 inch range with localized amounts near 3 inches. This
  could cause localized flooding on Wednesday.

- Confidence is high that much cooler and drier conditions will
  arrive for late week into the weekend.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 230 PM CDT Tue Jul 29 2025

Current Conditions and Synoptic Pattern: Water vapor and upper
air analysis continues to show a broad upper level high pressure
cell/ridge over the central US. Iowa remains along the northern
periphery of this and therefore continues to be susceptible to
ridge runners. 12z KDVN sounding showed strong inhibition
(convective temp 106F) in the wake of the early morning MCS and
therefore has created another tight instability gradient across
the area. The mesoscale features were quite messy with multiple
things going on this afternoon. The early morning MCS has pushed
an outflow boundary well south of the area into Missouri and
has essentially become diffuse. A surface low across southern MN
has draped another boundary east/southeast into northern
portions of the CWA where temps are slightly cooler with
northwest winds. Lastly, a weakening cluster of showers north of
Des Moines has an associated outflow boundary moving into the
southwestern CWA.

The airmass was slowly beginning to recover/destabilize early
this afternoon, especially along and south of I-80 where ML CAPE
was now up to around 2500 J/kg. Much higher instability exists
just west/southwest of the CWA. Temps were increasing into the
middle to upper 80s with dews in the middle to upper 70s along
and south of I-80.

This afternoon through this evening: low confidence forecast
for this time period as CAMS have struggled with morning/early
afternoon isolated storms across northern/central Iowa. One
thing that has occurred is that storms seem to weaken as they
approach our area which makes sense given the inhibition. We
will maintain low pops (10-30%) through the afternoon and
evening hours mainly due to presence of several mesoscale
features. However, it's likely many places remain dry. Last few
runs of the Warn On Forecast model shows a signal for a few pop
up storms south of I-80, closer to the Missouri border in the
3-6pm time frame. If a storm were to get organized, then
damaging winds would be the most likely hazard. Temps and heat
indices are generally on track with peak heat indices in the 95
to 105 range this afternoon/early evening. Highest values south
of I-80 where temps and dews are higher. Heat Advisory remains
in effect until 8pm.

Overnight through Wednesday: There is a good signal in the high
res guidance that a low level jet will develop overnight across
western Kansas into Nebraska. This combined with an incoming
shortwave and favorable upper level jet structure will allow for
another MCS to form. 12z HREF reflectivity paintball plots
suggest that this will likely form in/near Nebraska and then
roll/develop east overnight. Additional warm air advection type
activity may develop out ahead of it across the frontal
boundary that will be slowly sagging south into central Iowa.
Instability and shear would be favorable for this to be severe
as it approaches western portions of the CWA as early as 3am.
However, several CAMS show it moving in later. There is more
consensus that the MCS moves in closer to sunrise, lasting
through the morning hours. Instability will decrease with
eastern extent; therefore there is some question as to the
severe magnitude. Damaging winds gusts of 60-70mph will be a
concern as this MCS moves in, especially if it moves in as a
line segment as some of the 12z CAMS suggest.

Behind the complex, a lingering (but likely weakening) low
level jet, combined with a surface front and upper level lift
should allow for scattered showers and storms to last at times
through the morning and perhaps afternoon. If the morning MCS has
a strong enough cold pool, this could shunt the storms farther
south. However if it does not, then we will need to watch the
position of the front for additional strong to severe storms by
the afternoon if enough instability can return. Confidence is
low in the severe threat for tomorrow afternoon.

The other component is the heavy rainfall/localized flood
threat. HREF mean PW values increase to around 2.0in late
tonight through Wednesday. Therefore, plenty of moisture is
available for heavy rainfall/efficient rates. Furthermore, the
ECMWF EFI/Shift of tails tool suggests the potential for an
anomalously high rainfall event somewhere across
central/southern Iowa (generally the I-80 corridor). 12z HREF
qpf data suggests a footprint of 1-2 inches with localized
pockets of 3 inches across our area with higher amounts farther
west of the area. Currently, this looks to fall across a long
enough time period to not cause widespread flooding. However,
if that time window becomes shorter, then the flooding threat
could increase. We will continue to monitor the qpf forecasts
over the next 12-18 hours. Currently NBM high temps suggest
upper 70s to lower 80s tomorrow given the clouds/precip and
increasing northerly winds.

&&

.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
Issued at 230 PM CDT Tue Jul 29 2025

Ensembles are in strong agreement that a pattern change will
occur with the upper level high getting shunted farther
southwest, with northwest flow aloft developing over our area.
This will allow for a much cooler and drier air mass to move
into the area Thursday into the weekend. NBM high temp spreads
are quite small (2-4 deg) which leads to high confidence in
highs in the 70s and lows in the 50s. This is 10 degrees below
average for late July. Pops remain below 20 percent through
until Monday when the next disturbance moves in.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 700 PM CDT Tue Jul 29 2025

Scattered showers and thunderstorms are possible late tonight
which could bring brief heavy rainfall and MVFR/IFR conditions.
Confidence is low on the coverage and placement with this first
wave so mentioned potential in PROB30s. A more widespread round
of storms is expected Wednesday AM, moving through from west to
east. This could lead to a period of torrential rainfall and
gusty winds, along with brief IFR conditions. The active weather
continues through the end of the period with scattered showers
and isolated storms for Wednesday PM, which may be accompanied
by MVFR/IFR ceilings.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Heat Advisory until 8 PM CDT this evening for IAZ076>078-
     087>089-098-099.
IL...Heat Advisory until 8 PM CDT this evening for ILZ025-026-034-
     035.
MO...Heat Advisory until 8 PM CDT this evening for MOZ009-010.

&&

SHORT TERM...NWS
LONG TERM...NWS
AVIATION...Uttech

Hazardous Weather Outlook
National Weather Service Quad Cities IA IL
207 PM CDT Tue Jul 29 2025

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-301915-
Buchanan-Delaware-Dubuque-Benton-Linn-Jones-Jackson-Iowa-Johnson-
Cedar-Clinton-Muscatine-Scott-Keokuk-Washington-Louisa-Jefferson-
Henry IA-Des Moines-Van Buren-Lee-Jo Daviess-Stephenson-Carroll-
Whiteside-Rock Island-Henry IL-Bureau-Putnam-Mercer-Henderson-
Warren-Hancock-McDonough-Scotland-Clark-
207 PM CDT Tue Jul 29 2025

This Hazardous Weather Outlook is for portions of north central
Illinois...northwest Illinois...west central Illinois...east
central Iowa...northeast Iowa...southeast Iowa and northeast
Missouri.

.DAY ONE...THIS AFTERNOON AND TONIGHT

There is a low chance of a thunderstorm this afternoon and
evening, mainly south of Interstate 80. If a thunderstorm were to
form then lightning and damaging wind gusts would be the most
likely hazards. Most areas should remain dry.

Higher confidence that thunderstorms develop to the west tonight
and move towards the area after 3am, especially closer to sunrise.
Damaging wind gusts are the most likely hazard. The Storm
Prediction Center has a marginal, level 1 out of 5 risk, for
severe storms tonight.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

An ongoing round of thunderstorms is likely Wednesday morning with
damaging wind gusts and heavy rainfall the most likely hazards.
Localized flooding could also occur with this activity.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is possible by Wednesday morning.

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