Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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883
FXUS63 KDVN 212333
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
633 PM CDT Mon Jul 21 2025

.KEY MESSAGES...

- Dangerous heat and humidity expected for some Tuesday and then area-
  wide Wednesday into Thursday. An Extreme Heat Watch remains in
  effect.

- An active weather pattern is likely for late this week into
  the weekend.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 319 PM CDT Mon Jul 21 2025

Generally south to southeasterly flow will persist over the area
through Tuesday, thanks to a large area of high surface high
pressure over the Great Lakes region. Additionally, very pronounced
upper-level ridging is expected as a large upper-level bubble of
high pressure develops over the south-central CONUS. Ensemble and
CAM guidance both suggest pretty weak forcing for ascent in our
region tonight, so chances of showers and storms remain pretty
limited (less than 20% across the area). We do look to hold on to
partly to mostly cloudy skies in our CWA, with overnight lows
falling only to the upper 60s to lower 70s.

Attention then turns to the main focus for this week, which
continues to be a period of hot and very humid conditions Tuesday
through Thursday. At this point, confidence is highest for these
conditions Tuesday and Wednesday, and a bit lower for Thursday. More
on Wednesday and Thursday in the Long Term period. Now, for Tuesday,
the resulting warm air advection from the southerly flow will help
result in 850 mb level temperatures of 20 to 22 degrees C, which are
around the 90th percentile per the ECMWF climatological percentiles.
These temperatures, coupled with the fact that we are at our annual
peak for evapotranspiration of local crops, and we expect dew points
to rise to the middle to upper 70s across the area, which should
persist through at least Thursday. All of this should result in heat
index values between 100 to 110 degrees F for a sizable portion of
our CWA. There is the possibilty of a mid-level shortwave impulse to
sweep through the area Tuesday during peak heating, and if any
organized convection develops, this could throw a wrench in our
temperature/heat index values. However, the latest guidance has a
stronger signal for drier conditions than wet, which would keep the
hot and humid conditions in place. Given the uncertainty in how this
shortwave will impact these conditions, decided to hold on to the
Extreme Heat Watch for Tuesday through Thursday. However, it is
pretty noteworthy that the 21.12z HREF ensemble exceedance
probabilities of 100 degrees F heat indices are around 70 to 100%
for our southwestern half of the CWA, so confidence is very high for
the need of a Heat Advisory or Extreme Heat Warning. More on this in
the Long Term section.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
Issued at 319 PM CDT Mon Jul 21 2025

Hot and humid conditions are expected to continue Tuesday night
through at least Wednesday. Another noteworthy item regarding the
upcoming heat is the fact that the overnight lows Tuesday night into
Wednesday morning may offer little relief from the heat, with some
locations possibly not falling below 75 degrees F, which could
maintain heat stress for people that don`t have AC or any other
means to stay cool. Wednesday will likely have the highest heat
indices of this stretch, thanks to the ridge building even farther
north, placing us well within the heat dome, and no mid-level
shortwaves to kick-off any showers or storms. Heat indices will once
again be between 100 to 110 degrees F Wednesday, so the oppressive
heat and humidity will continue. Thursday could also be day of high
heat and humidity, although guidance suggests a cold front to
approach the region by late in the day. This could provide some
relief from the heat if we get any showers or storms to develop, but
uncertainty remains on how far southeast the front gets. Even if it
doesn`t precipitation, some convective debris could also provide
some relief from the heat, so this bears watching the trends of the
frontal arrival.

The aforementioned cold front will be moving across the region late
week and bring with it increasing storm chances with the potential
for some organized MCS activity and severe potential given the
degree of instability, which will need to be monitored in the days
ahead. Temperatures should cool a bit late week into next weekend,
but it still looks to be quite warm/hot and humid. Storm chances
will also exist as we will reside in the favorable location for
ridge-rider storm complexes in the `ring of fire` to the north of
the heat dome centered over the Southern Plains. This will be
accompanied by periodic heavy rain and severe weather threats.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 626 PM CDT Mon Jul 21 2025

Moist air remains over the region, and with that, low clouds
have been in place over Iowa and Illinois through the day, and
will likely be in place much of tonight into Tuesday morning. A
warm front is expected to lift north during the day, resulting
in stronger south winds, very warm conditions, and a scattering
out of cloud cover during the late morning and afternoon hours.
Winds should remain under 15ks through the period, but shift
from east/southeast to south/southeast by 15Z Tuesday.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Extreme Heat Watch from Wednesday morning through Thursday
     evening for IAZ040>042-053-054-066.
     Extreme Heat Watch from Tuesday afternoon through Thursday
     evening for IAZ051-052-063>065-067-068-076>078-087>089-
     098-099.
IL...Extreme Heat Watch from Wednesday morning through Thursday
     evening for ILZ001-002-007-009.
     Extreme Heat Watch from Tuesday afternoon through Thursday
     evening for ILZ015>018-024>026-034-035.
MO...Extreme Heat Watch from Tuesday afternoon through Thursday
     evening for MOZ009-010.

&&

$$

SHORT TERM...Schultz
LONG TERM...McClure/Schultz
AVIATION...Ervin