812
FXUS63 KDVN 261954
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
254 PM CDT Sun Jul 26 2026

.KEY MESSAGES...

- Oppressively humid through Monday evening (cannot get much
  more humid than this), with very little relief tonight,
  followed by Monday afternoon heat indices in many locations
  peaking 105-115.

- Scattered thunderstorms in the region through Monday, some
  potentially organized especially late tonight and Monday
  morning in northwest Illinois. These could be severe with
  damaging winds (level 2 of 5 risk) if well-organized.

- Some midweek relief behind a cold front Monday night, although
  smoke from Northwest U.S. and Canadian fires may spread over
  the area that could continue through Tuesday.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 250 PM CDT Sun Jul 26 2026

Dew points are at the true upper echelon over the area this
afternoon, with readings in the CWA between 78F and 82F at
almost all ASOS and AWOS locations, with exceptions being a few
AWOSs indicating 83F to 86F(!). Coupled with temperatures in
the upper 80s to mid 90s, this is providing heat index readings
of 100 to 115 for most locations. Such high dew points will
offer very little reprieve in cooling tonight, with lows in the
upper 70s apart from any convective influences. These lows will
be near record daily warm minimum temperatures.

For thunderstorm chances, through this evening there are a few
features we are watching that could provide an impetus. One is
the warm front near the Mississippi River, which separates
temperatures several degrees above 90F from upper 80s. Gradual
warm air advection (WAA) atop this has led to some better-
defined cumulus in parts of northwest and north central
Illinois, and cannot rule out a couple late afternoon storms
there. There`s also a remnant MCV over the southern CWA creeping
southeast. This will likely will spark storms but these may be
just beyond our CWA by the time they do (after 5 PM). Finally,
there is a short wave and mid-level speed max over far northwest
Iowa that will move over the area during this evening. That too
may be enough to pop isolated storms. But as is common in this
air mass that is highly moist (PWAT 2 inches) and conditionally
unstable (MUCAPE of 6,400 J/kg on our 18Z sounding), it is often
challenging to forecast areas and timing without some more
observational trends. The CAMs naturally struggle too. So just
have largely broad 20% chance PoPs to account for these.

For overnight into Monday morning, attention turns to the
northeastern side of the heat dome, from Wisconsin southward
into Illinois. This area will be under a seasonably strong belt
of upper level winds, and at the gradient of strong instability.
Well-defined mid level impulses are seen across the northern
half of Minnesota this afternoon, and these should be the
triggers for mature convection in Wisconsin this evening. More
than sufficient deep layer shear (>45 kt) and mid-level lapse
rates around 9 C/km should support upscale growth, and steering
vectors indicate that to be to the south-southeast. Multiple
clusters are favored, possibly even one well-defined mature MCS,
that most high-resolution models track from Wisconsin into
northern Illinois late tonight/early Monday morning. There is
spread in the longitude these storm clusters will take, and
accounting for larger than normal uncertainty given the pattern,
a reasonable western edge of the storm swath is a little west
of the Mississippi River. So all that said have inched up PoPs
some, especially in northwest Illinois, late tonight and Monday
morning, but the severe risk is at least part conditional on
storms being semi- or fully organized into clusters or an MCS.
The higher end scenario would be a quickly-propagating mature
MCS with a severe wind threat, potentially significant. The
more likely scenario is scattered to clusters of storms that
would have a scattered severe threat, especially in our far
eastern counties.

Outflows from this convection, even if the convection itself is
not in our area, are likely to track enough southwest into our
area in the morning. These could fester storms especially with a
western solution back to even the Mississippi River. This
outflow(s) along with any convective clouds lingering through
mid-morning is why we felt going with a Heat Advisory for
Monday in most of far northwest and north central Illinois was
the wiser route. Nonetheless, still oppressively humid, whether
highs are upper 80s or mid 90s, and thats the main message for
Monday. The 925 mb temperatures (25-30C) would support mid to
upper 90s area-wide at this time of year, so those locations
that do tap into more full sun, such as parts if not most of
eastern/southeastern IA and northeast MO, are favored to see
their highest heat index readings of the year (110-115F). Heat
safety is a must on Monday.

During the afternoon Monday, most locations look to be markedly
capped on forecast soundings, with the exception possibly being
the far east due to lingering boundaries and slightly cooler
700-850 mb air. All in all the chances for storms Monday
afternoon look low.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 250 PM CDT Sun Jul 26 2026

A cold front will progress southward on Monday night, with some
uncertainty how quickly it moves through the area. Because of
that and the very humid and hot conditions during the daytime
Monday, have the headlines going all the way through 10 PM. The
frontal convergence may be enough to overcome any weaknesses in
the cap, which again could be northwest Illinois but still an
overall low signal for convection in our CWA.

One note for behind the front is the potential for smoke in the
air, possibly even reduced air quality at the surface. GOES
Geocolor satellite this afternoon indicated widespread smoke
over the northern CONUS Rockies into the western Dakotas. RAP
and HRRR extended smoke forecasts indicate this being steered
southward behind the front over our area. This is still too far
out to tell if it would mix to near-surface, but at least some
smoky sky Monday night into early Tuesday looks probable.

After quiet and near to slightly warmer than seasonable
temperatures Wednesday and into the day Thursday, a slow moving
and fairly well-defined short wave is indicated by guidance to
pass over the area late Thursday night into Friday. This looks
like the next chance of rain.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1240 PM CDT Sun Jul 26 2026

A hazy afternoon with lingering MVFR ceilings along and east of
the Mississippi River, which will gradually lift and scour by
mid-late afternoon. Isolated storms could spark south of I-80
this afternoon, but too low of confidence to include in MLI and
BRL TAFs. For tonight, a few upper level disturbances will
traverse the region, and in such a moist atmosphere it will not
take much for scattered storms to develop. The main chances look
to be in northwest Illinois late tonight and Monday morning.
Because of this close proximity, have included PROB30s for TSRA
at DBQ and MLI.

Morning IFR, such as been seen the last two days, is currently
not anticipated for Monday. However, lingering haze is likely
and some low clouds would be possible in/near northwest
Illinois where boundary layer relative humidity is predicted to
be the highest.

Otherwise, southerly winds will prevail at TAF sites through
the period, with some 10-12 kt sustained Monday afternoon.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Extreme Heat Warning until 10 PM CDT Monday for IAZ040>042-
     051>054-063>068-076>078-087>089-098-099.
IL...Extreme Heat Warning until 10 PM CDT Monday for ILZ015-016-
     024>026-034-035.
     Heat Advisory until 10 PM CDT Monday for ILZ001-002-007-009-
     017-018.
MO...Extreme Heat Warning until 10 PM CDT Monday for MOZ009-010.

&&

$$

SHORT TERM...Friedlein
LONG TERM...Ellingworth/Friedlein
AVIATION...Friedlein