519 
FXUS63 KILX 200536
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1236 AM CDT Sun Jul 20 2025

.KEY MESSAGES...

- Thunderstorm activity both tonight and Sunday night will be
  capable of intense rainfall, with an associated threat of flash
  flooding. The storms Sunday night will be occurring in areas
  that saw intense rainfall earlier on Saturday. 

- A heat wave will impact the area from Tuesday through the end of
  the week, with the worst conditions Wednesday and Thursday.
  Chances of the heat index reaching higher than 110 degrees on
  these days are around 40-50%.

&&

.SHORT TERM...  (Through Monday Night)
Issued at 235 PM CDT Sat Jul 19 2025

MCS which has been impacting the forecast area much of the day is
finally waning. Hefty rain accumulation of 2-4 inches occurred in
a stripe from near Macomb southeast through Decatur, with a
separate area of 4-6 inches near Flora. The activity has pushed
the effective boundary well into southern Illinois, where new
thunderstorm development is taking place. For the remainder of the
afternoon, lingering showers and isolated thunderstorms south of
I-72 will continue to diminish, and some clearing will spread into
areas northwest of the Illinois River.

Main concern for this part of the forecast will be with additional
nocturnal MCS activity both tonight and Sunday night. A weak
surface boundary will set up near or just south of I-80 this
evening, drifting southward a bit overnight. Synoptic models
show the main MCS activity developing over Iowa and eastern
Nebraska this evening, then tracking across the northern third of
Illinois overnight into Sunday. However, a few of the high-res
models suggest some scattered activity this evening roughly near
the I-74 corridor, so some 20-30% PoP's will be included in that
area for the evening hours. With precipitable water values in the
2-2.3 inch range, and warm cloud depths around 14kft, very heavy 
rain remains a concern tonight. Since the I-74 corridor missed out
on the soaking rains today, flood headlines will be held off for 
now, but this will need to be watched closely.

Development of Sunday afternoon and evening activity will depend
on where the boundary from the overnight convection lays out, but
highest PoP's will be maintained during the day near I-74. Thinking
is that the threat Sunday night will be further south into central
Illinois, with little chance of recovery for the areas that were
dumped on today. Flood headlines will also need to be considered
for Sunday night by future shifts. 

Extent of the clouds/rain will complicate temperatures on Sunday
as well, but the areas south of I-72 should stay dry enough that
heat index values reach 100-105 in the afternoon. With a more
widespread cloud cover and lingering rain Monday, temperatures
should be held down into the mid 80s in most areas.

Geelhart

.LONG TERM...  (Tuesday through Next Saturday)
Issued at 235 PM CDT Sat Jul 19 2025

Focus during this portion of the forecast remains on the intense 
heat. Ring-of-fire pattern will begin in earnest over the central
U.S. on Monday, with a ridge axis and the center of upper level 
high pressure over the lower Ohio Valley by early Wednesday. Core
of the heat wave still looks to be on Wednesday and Thursday, 
with widespread afternoon heat index values of 105-115, especially
if dew points get up to near 80F (plausible with the amount of 
rain we're concerned with over the next couple of days). WPC heat
index guidance shows about a 40-50% chance of 110+ on both
Wednesday and Thursday. Late in the week, the ridge gets more 
elongated from west to east, slowing any substantial cooling 
trend, and heat index values over 100 still appear likely.

MCS activity will be shunted north next week as the ridge builds,
but as we get toward Friday and Saturday, the flattening of the
ridge will bring the rain threat southward into our area. 

Geelhart

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1236 AM CDT Sun Jul 20 2025

Multiple rounds of showers and thunderstorms in the vicinity of a
slow moving frontal zone across central IL can be expected through
the upcoming 24 hours. The first thunderstorms look to develop
near the I-74 corridor in west central IL spreading southeastward
through the early morning. The highest thunderstorm chances look
to migrate southward late in the forecast period, closer to the
I-72 corridor. The first few to several hours will be generally 
VFR, however any time after that, MVFR or worse conditions will be
possible. Winds will be generally light and variable through the
period.

37

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$