116
FXUS63 KILX 121702
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1202 PM CDT Sat Sep 12 2026

.KEY MESSAGES...

- A stalling cold front creates a sharp temperature split
  Sunday, with highs ranging from the upper 70s northwest of
  the Illinois River to near 90 south of I-70. Scattered showers
  (20-40% chance) will be near the front.

- Multiple rounds of thunderstorms track along a stalled front
  Tuesday and Wednesday, especially north of I-72. There will
  be a low risk for strong to severe storms and locally heavy
  rain.

- Periodic thunderstorm chances persist Thursday and Friday
  along the lingering front, maintaining a tight temperature
  gradient across central and southeast Illinois.

&&

.DISCUSSION...
Issued at 1202 PM CDT Sat Sep 12 2026

A weak cool front was pushing into northwest IL at midday,
associated with a band of mid level clouds. HRRR and RAP
forecast soundings indicate a prominent thermal ridge advecting
into central Illinois ahead of the front, with 850 mb
temperatures approaching 17-19 C. High temperatures reach the
upper 80s, with a few locations topping out near 90 degrees
under mostly sunny skies. The dry and warm air mass aloft caps
surface- based parcel ascent across central Illinois, so we
maintain a dry forecast through tonight.

The surface boundary stalls across the forecast area on Sunday.
HREF guidance shows a tight temperature gradient developing
across the local area. Highs range from the mid-to- upper 70s
northwest of the Illinois River to the lower 90s south of
Interstate 70. A persistent warm nose around 750 mb caps deep
convection along the front on Sunday, however weak isentropic
ascent generates saturation aloft, leading to mostly cloudy
skies and scattered showers. HREF ensemble probabilities keep
measurable precipitation chances between 20-40% north of I-70,
with QPF under a tenth of an inch.

An upper-level trough moves across the Northern Plains Monday,
pushing a surface front into the Upper Midwest. Decaying
nocturnal convective remnants reach far western Illinois Monday
morning, but dry conditions are forecast across central and
southeast Illinois. Highs to be seasonable in the upper 70s to
mid 80s.

The pattern turns active Tuesday and Wednesday as a surface low
tracks toward Hudson Bay, driving a cold front into northern or
central Illinois where it stalls. ECMWF and GFS solutions show
500 mb flow turning southwesterly, placing the region under
favorable upper-level jet dynamics. Moderate instability
combines with low-moderate deep layer shear to support
organized convective structures. CIPS/CSU machine learning and
AI guidance highlight a low potential for severe thunderstorms
Tuesday afternoon and Wednesday.  Convective training along the
quasi- stationary boundary brings a risk for heavy rainfall
Tuesday into Wednesday. WPC Excessive Rainfall Outlooks
maintain a Marginal to Slight Risk across central Illinois. LREF
ensemble probabilities show a 40-60% chance for 24-hour QPF
exceeding 1.0 inch north of a Beardstown to Bloomington line,
with 48-hour NBM mean precipitation totals exceeding 2.0 inches
in far northwest counties near Galesburg. To the south of the
active storm clusters, a late season hot and humid airmass will
prevail with highs in the low-mid 90s, and peak daily heat
indices topping 100 degrees.

The baroclinic zone remains positioned over the region Thursday
and Friday, though with less upper level support, PoPs are
reduced to around 30% and severe/heavy rain risks appear quite
low. High temperatures maintain a north-to-south gradient,
ranging from the upper-70s near Galesburg to the lower 90s near
Lawrenceville.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1202 PM CDT Sat Sep 12 2026

A cold front was nearing western IL at midday. Light SW winds
ahead of the front will veer NW behind the front this evening,
then NE by late Sunday morning. A band of MVFR ceilings along
the front is forecast to rise above 3k feet and scatter out
before reaching the central IL terminals. An upper level
disturbance will bring scattered -SHRA on Sunday, however these
are not expected to reduce flight category.

&&

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

&&

$$

KEY MESSAGES...25
DISCUSSION...25
AVIATION...25