077
FXUS63 KILX 220531
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1231 AM CDT Tue Jul 22 2025

.KEY MESSAGES...

- Hot and humid weather will be the rule Tuesday through Friday as
  afternoon heat index readings peak well above 100 degrees each
  day.

&&

.DISCUSSION...
Issued at 102 PM CDT Mon Jul 21 2025

High pressure anchored over the Great Lakes has nudged a cold front
just S/SW of the KILX CWA today...with 17z/12pm obs suggesting
the boundary is near a Hannibal, Missouri to Paducah, Kentucky
line. While surface winds are light from the NE behind the
boundary, not much drying is seen until well northeast of the I-74
corridor across northeast Illinois and northwest Indiana where
dewpoints have dropped into the lower to middle 60s. A robust Cu-
field has developed well north of the front across much of central
Illinois closer to the dewpoint gradient and would not be
surprised to see widely scattered showers/thunder developing
across this area over the next few hours. Any showers that form
will quickly dissipate toward sunset, followed by a dry evening
across the board. Will have to keep an eye on the boundary as it
begins to slowly inch northward into southern Iowa and western
Illinois late tonight. The nocturnal jet may interact with the
front to trigger isolated convection...primarily along/southwest
of a Macomb to Taylorville line overnight.

As upper ridging builds over the Mississippi River Valley, it
will push the main baroclinic zone well to the north into the
Upper Midwest/Great Lakes by late Tuesday, which will allow a
heatwave to develop across much of the Midwest. A continued
easterly component to the wind will keep temperatures in the upper
80s to around 90 degrees on Tuesday: however, as winds veer to
S/SW, readings will climb into the lower to middle 90s Wednesday
through Friday. After the recent heavy rainfall and with crops
still actively growing and contributing additional moisture to the
atmosphere, surface dewpoints will hover in the middle to upper
70s...with lower 80s at times in a few spots. These high dewpoints
will result in peak afternoon heat index values of 105-115
degrees across the board. Slight cooling may be noted by next
weekend as a short-wave trough flattens the upper ridge and nudges
a frontal boundary southward toward central Illinois: however,
confidence in this scenario remains low. At this point, be
prepared for an oppressively hot and humid period from Tuesday
through at least Friday.


Barnes

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1231 AM CDT Tue Jul 22 2025

Weak warm advection north of a surface front to the south will
produce increasing low cloud cover overnight, while winds will be
light enough and skies clear enough early on that visibility will
likely lower with at least a thin fog developing. It is hard to
pinpoint whether stratus or fog will become dominant, but it
appears at least periods of IFR cigs and/or vsbys will develop by
sunrise. After sunrise, cigs will gradually lift and vsbys will
improve, however a period of MVFR cigs will likely continue until
around 18Z before SCT-BKN cloud cover around 4000 ft AGL becomes
dominant. Winds SE 3-8 kts through the period.

37

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Extreme Heat Watch from noon CDT today through Thursday evening
for ILZ027>031-036-037-040>042-047>052.

Extreme Heat Watch from Wednesday morning through Thursday
evening for ILZ038-043>046-053>057-061>063-066>068-071>073.

&&

$$