460
FXUS63 KILX 062303
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
603 PM CDT Sun Sep 6 2026

.KEY MESSAGES...

- Heat Returns Midweek: Hot and muggy conditions return Tuesday
  and Wednesday. Temperatures will top out in the 90s both days,
  with an influx of moisture pushing heat indices to around 100
  degrees south of I-72 Wednesday afternoon.

- Midweek Storm Potential: A passing front brings a 40-60%
  chance for scattered showers and thunderstorms on Wednesday,
  primarily across the Illinois River Valley.

- Higher Storm Chances Late Week: Confidence is higher (60% to
  80% chance) for widespread thunderstorms Wednesday night into
  Thursday morning, especially along and south of I-72.

&&

.DISCUSSION...
Issued at 125 PM CDT Sun Sep 6 2026

SHORT TERM... (This afternoon through Monday night)
A welcome break from the recent heat wave will be in place this
afternoon as the strong upper-level ridge has retrograded to
our west and is now centered over the central Great Plains,
while surface high pressure centered over the Great Lakes
maintains a modest northeasterly breeze across central Illinois.
This setup is drawing in a much drier airmass, with afternoon
temperatures topping out in the 80s and dewpoints mixing down
into the upper 50s and lower 60s.

Quiet and pleasant conditions will persist into Monday. Low
temperatures Monday morning will drop into the 60s. As the
surface high slides eastward, winds will veer to the east-
southeast, allowing afternoon highs to once again top out in the
low to mid-80s under mostly sunny skies.

.LONG TERM... (Tuesday through Friday)
The respite from the heat will be short-lived as summer-like
conditions return mid-week. An upper-level low currently over
the Pacific Northwest is projected to track eastward into the
Canadian Prairies Monday night into Tuesday, flattening the
central U.S. ridge and spreading its eastern periphery back
across the Midwest. A corresponding 850mb thermal ridge (with
temperatures climbing to 22-24C, reminiscent of the recent heat
wave) will shift east over central Illinois on Tuesday,
lingering over southern Illinois into Wednesday. Consequently,
afternoon highs will surge back into the 90s across most of
central Illinois on Tuesday. Fortunately, deep boundary layer
mixing on Tuesday afternoon should keep dewpoints relatively
dry -- generally in the upper 50s to mid-60s -- which will keep
heat indices in check. Moisture returns in earnest on Wednesday
as southwesterly flow strengthens ahead of an approaching cold
front. This flow will transport a muggier airmass, boosting
dewpoints into the upper 60s to mid-70s. Combined with
temperatures in the 90s, heat indices are expected to exceed 100
degrees in several locations Wednesday afternoon, particularly
south of the I-72 corridor.

The trailing cold front is modeled to sag south-southeastward
into central Illinois on Wednesday in response to the parent
surface low lifting across Manitoba and toward Hudson Bay.
Although National Blended of Models (NBM) PoPs have trended
upward (now around 60% in the Illinois River Valley with frontal
passage), model guidance remains split on how far southeast the
initial precipitation band will penetrate. The primary limiting
factors for widespread rainfall Wednesday afternoon include
weak low-level convergence near the frontal zone (as central
Illinois sits near a col/neutral point) and a lack of strong
upper-level support, with the primary 500mb trough axis
tracking well to our north across the Great Lakes. Higher
confidence precipitation chances (60-80% PoPs, especially along
and south of I-72) are expected Wednesday night into Thursday
morning. This convective signal is driven by a strengthening
low-level jet which will overrun the stalling frontal boundary
and trigger renewed, widespread thunderstorm development. Behind
this front, temperatures will trend cooler and more
comfortable, retreating back into the 80s for the remainder of
the work week.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 555 PM CDT Sun Sep 6 2026

An expanding upper ridge will suppress any active weather across
the central Illinois terminals through Monday. Skies will remain
mostly clear with lights winds through the TAF period.

&&

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

&&

$$

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