604
FXUS63 KILX 141113
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
613 AM CDT Mon Sep 14 2026

.KEY MESSAGES...

- Near-term conditions remain dry and pleasant today, with
  increasing southeasterly winds gusting 15-25 mph this
  afternoon.

- Active weather returns Tuesday and Wednesday as a cold front
  stalls across central Illinois, bringing multiple rounds of
  showers and thunderstorms through the end of the week and
  weekend.

- Severe weather is possible both Tuesday and Wednesday, with
  localized heavy rainfall (1-2+ inches, particularly
  northwest of a Havana to Bloomington line).

- A strong north-to-south temperature contrast will exist
  across the stalled boundary mid-to-late week, with highs
  ranging from the lower 80s north to 90s south.

&&

.DISCUSSION...
Issued at 218 AM CDT Mon Sep 14 2026

Today and Tonight...
Early this morning, high pressure centered over Lake Michigan
is delivering a crisp, fall-like morning across central
Illinois, with temperatures predominantly in the 50s under light
easterly winds. To the west, a closed upper-level low is
lifting across the Canadian Rockies with surface cyclogenesis
ongoing over the northern Great Plains. An associated warm front
is advancing northward through the Great Plains, supporting
convective activity focused across the mid and upper Missouri
River Valley.

This convection will largely remain west of the local area
today as it lifts into the Upper Midwest. However, there is a
minor (10-15%) chance for a few lingering showers or an isolated
thunderstorm to clip far northwestern counties north of the
Illinois River late morning into early afternoon. Otherwise, dry
conditions will prevail today. Southeasterly winds will
strengthen and become breezy as the surface pressure gradient
tightens from the west, with gusts of 15 to 25 mph expected this
afternoon. Temperatures will be near seasonal norms, with highs
around 80 along the I-74 corridor and in the low-to-mid 80s
across the remainder of central Illinois.

Tuesday and Wednesday...
The northern Plains surface low will continue to deepen while
lifting across the Canadian Prairies toward Hudson Bay Tuesday.
A trailing cold front will sweep across the Upper Midwest, with
its southern extension reaching central Illinois Tuesday
afternoon. Widespread showers and thunderstorms are expected
along and ahead of this boundary, persisting into Wednesday as
the frontal zone becomes oriented parallel to mid/upper-level
flow and stalls directly across central Illinois.

Severe Weather Potential:
The severe threat warrants close monitoring. Deep layer shear of
30-40 kt, enhanced by an upper-level jet streak over the Upper
Midwest, will overlap the frontal boundary. GFS guidance
suggests pockets of 1000-1500 J/kg MLCAPE developing Tuesday,
increasing to 1500-2000 J/kg on Wednesday. This thermodynamic
and kinematic environment will support organized convection
capable of isolated severe wind gusts. Colorado State University
(CSU) machine learning probabilities indicate a 15-30% severe
risk Tuesday and 5-15% Wednesday across central Illinois. The
Storm Prediction Center (SPC) has a Marginal Risk (Level 1 of 5)
for most of central Illinois Tuesday and a risk area may be
introduced Wednesday once forecast details come into better
focus.

Heavy Rainfall Threat:
In addition to severe potential, heavy rainfall and localized
flooding will be concerns as multiple convective rounds train
along the lingering frontal boundary. NBM 48-hour mean QPF
ending Wednesday night indicates 1.00+ inch amounts north of a
Havana to Bloomington line, with 2.00+ inch QPF contour edging
into far northwestern sections just north of Galesburg.

Temperature Disparity:
A sharp thermal gradient will develop across the frontal zone
Tuesday and Wednesday. North of the boundary, cloud cover and
precipitation will cap highs in the lower-to-mid 80s. South of
the boundary, filtered sunshine will allow temperatures to climb
into the low-to-mid 90s with elevated humidity as dew points
climb back into the lower 70s. Triple digit heat indices will be
the result, especially along and south of the I-72 corridor.

End of the Week and Weekend...
Unsettled weather will persist into Thursday and Friday as the
baroclinic zone remains draped across northern and central
Illinois. Global models (specifically ECMWF and GFS) have begun
to converge on a solution keeping the boundary anchored across
portions of central and northern Illinois. Consequently, daily
chances for convection will continue alongside lingering
90-degree heat across southern portions of the forecast area.
Little pattern change is anticipated heading into the weekend,
maintaining periodic shower/thunderstorm chances and a strong
north-to-south temperature contrast across the region.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 612 AM CDT Mon Sep 14 2026

A warm front will lift across the region today with easterly winds
in place early this morning turning southeast ahead of the
front, then southerly late this evening with its passage. Winds
will be strongest in western Illinois where the gradient is
tightest, and gusts to around 20 kt are expected at PIA/BMI/SPI.
A low level jet will develop this evening just west of the
terminals. This will result in low level wind shear at the
western sites. VFR conditions are expected through the period.

&&

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

&&

$$

KEY MESSAGES...Deubelbeiss
DISCUSSION...Deubelbeiss
AVIATION...Deubelbeiss