327
FXUS63 KILX 060509
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1209 AM CDT Sun Sep 6 2026

.KEY MESSAGES...

- Dangerous heat continues across central Illinois through
  early evening, with peak heat index values ranging from 100 to
  110F.

- A cold front brings welcomed relief Sunday and Monday,
  pushing high temperatures into the 80s for most locations and
  dropping heat indices into the 80s and 90s.

- High heat and humidity return Tuesday and Wednesday, bringing
  another risk for triple-digit heat index values.

&&

.DISCUSSION...
Issued at 113 PM CDT Sat Sep 5 2026

A backdoor cold front continues its slow southward progression
across central Illinois this afternoon. Ahead of the boundary, a
deeply mixed boundary layer under partly cloudy to mostly sunny
skies is allowing temperatures to surge into the upper 90s,
with a few locations potentially reaching triple digits. This is
supported by the 12Z ILX sounding, which sampled 850mb
temperatures of 21C -- well above the 90th percentile (18.6C)
for early September. Extremely high humidity is driving peak
heat index values between 100-110F through early evening.

Behind the front, winds will shift from northwest to northeast,
gradually pushing a slightly drier air mass into the region.
Overnight lows will finally offer relief, dropping into the 60s
for most areas -- the coolest readings since the current
heatwave began in late August.

For Sunday and Monday, the backdoor front will bring a welcomed
break to the oppressive heat, particularly across northern and
central portions of the forecast area, where highs will top out
in the mid-to-upper 80s. Further south, closer to the front,
temperatures will remain slightly elevated in the lower 90s.
More comfortable conditions will arrive as drier air filters in
from the northeast on Sunday, with dew points eventually
bottoming out in the mid-50s to low 60s by Monday afternoon.
Consequently, peak heat indices both days will remain in the 80s
and 90s.

.LONG TERM... (Tuesday through Friday)
Relief will be short-lived as the strong upper-level ridge is
progged to expand back eastward into the Midwest by Tuesday and
Wednesday. This will trigger a resurgence of widespread
90-degree temperatures, with triple-digit heat index values once
again possible.

By mid-week, a closed upper-level low over the Pacific
Northwest will open and advance east across the Canadian
Prairies, buckling the upper ridge. In response, a surface low
will deepen as it lifts across Manitoba on Tuesday and toward
Hudson Bay on Wednesday. The trailing cold front will sag
southward into the Upper Midwest, with its southern tail / col
area eventually pushing into central Illinois on Wednesday.
Precipitation chances with this frontal passage remain quite low
(10-20%) due to weak convergence and the displacement of the
primary upper-level support far to the north.

Chances for more substantial rainfall increase (40-50%)
Thursday night into Friday morning. This is in response to a
strengthening low-level jet to our west, which will drive
renewed thunderstorm development along the stalling frontal
boundary.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1209 AM CDT Sun Sep 6 2026

An area of ceilings just above 1,000 feet is pushing southwest,
with the leading edge extending from about KBMI-KCMI this hour.
The low clouds are guided by northeast winds near 10 knots.
Model guidance and ensembles are suggesting about a 4-5 hour
period of MVFR conditions at each TAF site, and the band of low
clouds should be southwest of the terminals by 12-13z. After
that, clouds into Sunday evening should just be scattered.

Northeast winds will prevail through the period. Some winds near
10 knots are occurring near the leading edge of the cloud deck
and should subside for a time, but pick up again Sunday morning
after skies clear.

&&

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

&&

$$

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