566
FXUS63 KILX 190745
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
245 AM CDT Tue Aug 19 2025

.KEY MESSAGES...

- Hot and humid conditions continue south of I-70 today, where
  afternoon heat indices of 100 to 105 are expected. A cold front
  will move through today though, resulting in temperatures
  returning to near normal for the rest of the work week.

- Scattered storms are possible (20-40% chance) through the
  afternoon, mainly south of I-72/Danville. Isolated strong wind
  gusts are possible with these storms.

&&

.DISCUSSION...
Issued at 242 AM CDT Tue Aug 19 2025

A convective complex was ongoing at 2am/07z, with outflow draped
between the I-55 and I-72 corridors and storms located to the
immediate west of the OFB. The main forecast change is a faster
southward progression of the frontal boundary, due in part to
these ongoing storms. The 19.00z guidance suite generally had a
good handle on these expectations.

While the front will push south of the area
today, the air immediately behind the front will still be muggy
with dewpoints staying in the mid 70s for much of the day
(although slightly lower dewpoint air should start to push in from
the north tonight). The expectation is that temps will still warm
into the 90s south of I-70 ahead of the front, although the
ongoing convection does add a layer of uncertainty as to whether
or not these temps are reached. The 19.00z HREF had a 60-80%
probability of heat indices reaching at least 100 south of I-70,
so opted to hoist one last heat advisory for Effingham to Crawford
county and southward.

The faster frontal progression should also mean a faster end to
precip across the area, with chances ending from NW to SE through
the day. For the daytime hours, scattered precip will mainly be
focused south of I-72/Danville (20-40%), shifting south of I-70
by early evening, and out of the area by late evening. Similar to
previous days, a few storms could produce strong to severe wind
gusts owing to strong instability, but weak shear will limit a
more organized severe threat.

Once this front departs, the rest of the week should be dry
(precip chances below 10%) with seasonable temperatures (highs in
the mid 80s). While NNE sfc winds on Wed could enhance low-level
moisture in east-central IL due to fetch off Lake Michigan, fcst
soundings show modest capping in place to stymie any shower
activity, at least in our CWA. Dewpoints gradually trend lower and
are expected to fall into the mid 60s by Thurs-Fri.

*** THIS WEEKEND INTO NEXT WEEK ***

There is still a strong signal for below normal temps in the
extended as an upper wave pushes across the northern Great Lakes
and sends a cold front through IL late Fri or during the day Sat.
Still think there is a some precip potential with this front,
although it`s unlikely to amount to much as synoptic forcing aloft
will be quite limited and the best instability trails behind the
front. Blended guidance still has PoPs at just 10%, with the low
values likely due in part to timing differences with the front, as
well as placement differences and limited precip coverage.

This post-frontal airmass should provide an early taste of fall,
with high temperatures likely falling into the 70s. The NBM has a
20- 40% chance for highs above 80F north of I-70 on Sun, and just
a 10- 30% chance area-wide next Mon. The cooler temps will also be
accompanied by lower dewpoints, with the model blend dropping
dewpoints into the mid 50s.

Erwin

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1227 AM CDT Tue Aug 19 2025

A decaying line of showers and thunderstorms is pushing across
central Illinois early this morning ahead of a cold front. Have
therefore maintained the TEMPO group for TSRA between 07z-10z at
KPIA/KBMI/KCMI, but have downgraded to PROB30 further south at
KSPI/KDEC. Ceilings will lower for a brief time late this morning
in the vicinity of the cold front, mainly at KPIA/KBMI where MVFR
conditions are most likely (> 60% probability). Clouds eventually
lift and scatter across the board this afternoon, with winds
veering from west to north by sunset.

MJA

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon today to 7 PM CDT this evening for
ILZ066>068-071>073.

&&

$$