547
FXUS63 KILX 191641
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1141 AM CDT Sat Sep 19 2026

.KEY MESSAGES...

- A Marginal Risk (level 1 of 5) for severe weather exists
  across parts of central Illinois both today and Sunday. The
  primary hazard will be isolated strong wind gusts.

- Much cooler conditions will be on tap next week as high
  temperatures dip into the 60s everywhere north of the I-70
  corridor Monday and Tuesday.

&&

.DISCUSSION...
Issued at 348 AM CDT Sat Sep 19 2026

08z/2am radar imagery shows a large cluster of convection along
the Illinois/Wisconsin border. The storms are occurring ahead of
a weak area of low pressure analyzed over northern Iowa and are
being fed by a 30-40kt 850mb jet streak oriented from the
Central Plains to the southern Great Lakes. The convection will
continue to track E/SE across northern Illinois and will remain
largely north of the KILX CWA this morning. Have featured 30-60
PoPs along/north of I-74 through midday in case some of the storms
are able to drop/develop that far south as the main cluster
pushes into northern Indiana.

A prominent outflow boundary is currently evident from near
Waukegan to Moline...and this feature will likely serve as a
focus for additional convective development this afternoon as it
sags further southward. Most CAMs key in on locations along/east
of a Champaign to Shelbyville line after 20z/3pm. While the
atmosphere will be moderately unstable with SBCAPEs greater than
3000J/kg, weak 0-6km wind shear of less than 30kt will inhibit
widespread storm organization. As a result, am only expecting
isolated marginally severe wind gusts of 50-60mph with the
strongest cells.

As the nocturnal low-level jet shifts a bit further southward
tonight, showers and thunderstorms will become more widespread
across the N/NW CWA after dark. Based on the latest model
guidance, have opted to carry 60-80 PoPs along/north of a
Rushville to Normal line. Further southeast, locations along and
south of the I-70 corridor will remain dry through the entire
night.

With a short-wave trough interacting with a stationary frontal
boundary draped across the region, showers and thunderstorms
will continue into Sunday. While instability will be slightly
lower than today, an uptick in wind shear associated with the
wave will lead to a somewhat better chance for strong to
potentially severe storms during peak heating. NAM SBCAPEs reach
2000-2500J/kg while 0-6km bulk shear increases to around 30k by
afternoon. Given these parameters and a consistent reflectivity
signal noted by the RRFS, think some of the storms late Sunday
afternoon and evening will be capable of marginally severe wind
gusts/hail. The latest SPC Day 2 Convective Outlook highlights
areas along/south of a Rushville to Bloomington line for a
Marginal Risk (level 1 of 5) for severe weather. This seems
reasonable, although it may need to be nudged northward a bit if
RRFS trends continue.

Wet weather will continue on Monday and even into Tuesday as an
upper low evident on latest water vapor imagery over Idaho
gradually traverses the region. Once the low passes to the east,
synoptic subsidence will lead to a return to dry weather for
the remainder of next week. The big story will be the cooler
temperatures as highs drop into the 60s north of the I-70
corridor Monday and Tuesday, then only slowly rise back into the
70s as the week progresses. The coolest period continues to be
Tuesday night when lows reach the lower to middle 50s. A few
favored low-lying spots may even dip into the upper 40s as the
00z NBM indicates a 30-50% chance of temps below 50 degrees by
12z Wednesday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1136 AM CDT Sat Sep 19 2026

Morning showers and thunderstorms have pushed multiple outflow
boundaries across the regional terminals, making winds highly
variable early this afternoon. However, with a surface warm
front positioned up around Interstate 80, we anticipate winds to
become more uniformly from the south through late afternoon, but
with sustained winds less than 10 kts.

Flight conditions are forecast to remain VFR through at least
06z. Beyond that time, scattered showers and isolated
thunderstorms may begin to creep in from the north and west.
While the probability of showers and thunderstorms remains low
(30% chance), we did feel it necessary to maintain the PROB30
mention of -TSRA at the KPIA/KBMI/KCMI terminals Saturday
morning.

&&

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

&&

$$

KEY MESSAGES...Barnes
DISCUSSION...Barnes
AVIATION...MJA