962
FXUS63 KILX 211033
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
533 AM CDT Mon Sep 21 2026

.KEY MESSAGES...

- Much cooler weather will prevail this week as high
  temperatures only reach the 60s and lower 70s everywhere north
  of I-70 today through Wednesday.

&&

.DISCUSSION...
Issued at 301 AM CDT Mon Sep 21 2026

07z/2am surface analysis shows a slow-moving cold front
extending from West Virginia to southern Missouri while a 1030mb
high pressure is anchored over Ontario. An influx of cooler/drier
air from the northeast has led to mostly dry conditions north
of the I-72 corridor early this morning. However further south,
the nocturnal low-level jet continues to interact with the
departing boundary to trigger clusters of showers and
thunderstorms. The precipitation has been most widespread
along/south of a Jacksonville to Mattoon line, and this will
continue to be the case for the next couple of hours before the
best forcing shifts E/SE into the Ohio River Valley and the
showers taper off toward dawn. Despite a prominent decrease in
areal coverage, think widely scattered showers will continue to
be possible throughout the day as an upper low spinning over
Nebraska slowly pivots eastward. Forecast soundings suggest the
low overcast currently in place will persist as well, resulting
in a cloudy and cool day. High temperatures will range from the
middle to upper 60s along/north of I-72 to the upper 70s far
southeast around Flora and Lawrenceville.

Isolated showers will persist tonight into Tuesday morning as
the upper low gradually shifts into north-central Illinois. Once
this feature pushes to the east, synoptic subsidence on its
back side will lead to an end to the very light precip and
partial clearing by Tuesday afternoon. Highs on Tuesday will be
similar to today, ranging from the middle 60s far north to the
middle 70s south of I-70. As skies clear and winds diminish,
radiational cooling will lead to the coolest night of the
forecast period Tuesday night. Overnight lows will drop into the
lower to middle 50s, but may dip into the upper 40s in a few
low-lying rural locations west of I-57. Probabilities for temps
below 50 degrees have lowered across east-central Illinois
where partial cloud cover and a lingering breeze may limit
cooling: however, the 00z NBM still indicates a 50-60% chance
northwest of the Illinois River.

After that, the departing upper low is progged to linger over the
Mid-Atlantic...creating a blocking pattern across the eastern
CONUS. As a result, upper heights will gradually rise as ridging
builds over the Midwest by the end of the week through early
next week. The end result will be mostly dry weather with slowly
warming temperatures climbing back into the upper 70s/lower 80s
by next Sunday/Monday.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 533 AM CDT Mon Sep 21 2026

Showers and thunderstorms that tracked along/south of the I-72
corridor overnight are currently pushing eastward into Indiana
and will be well E/SE of the central Illinois terminals by 12z.
Despite an end to the rainfall, low clouds will persist through
the entire day. Ceilings have been IFR over the past several
hours: however, E/NE winds are bringing slightly drier boundary
layer in from the Great Lakes and causing ceilings to improve to
MVFR along/north of the I-74 corridor. Models are not handling
this particularly well, so am basing the 12z TAFs largely upon
observational trends. As a result, have opted to start
KPIA/KBMI/KCMI at MVFR...then raise KDEC to MVFR by 15z and
KSPI by 16z. The cloud cover will hold firm through tonight:
however, there are some indications the northern sites may
scatter overnight. Based on the HRRR/CONSSHORT forecast, have
gone with VFR conditions at KPIA after 07z and at KBMI after
09z. Further south, have maintained MVFR. Winds will be NE at
10-15kt through the entire 12z TAF period.

&&

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

&&

$$

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