489
FXUS63 KILX 121056
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
556 AM CDT Sat Sep 12 2026

.KEY MESSAGES...

- Temperature Spread Sunday: A stalling cold front creates a
  sharp temperature split Sunday, ranging from the mid 70s north
  of the Illinois River to near 90 south of I-70. Light showers
  or sprinkles (20-30% chance) remain possible along the
  boundary.

- Midweek Storm Potential: Multiple rounds of thunderstorms
  arrive Tuesday into Wednesday. There is potential for
  localized heavy rainfall exceeding 1-2 inches, especially
  north of Beardstown to Bloomington, along with a potential for
  severe weather.

- Late-Week Uncertainty: Unsettled conditions persist Thursday
  and Friday with periodic rain chances, though high uncertainty
  remains regarding exact frontal placement and daily
  temperature trends.

&&

.DISCUSSION...
Issued at 207 AM CDT Sat Sep 12 2026

     This Weekend...
This morning a closed upper low is pushing east across the mid
Mississippi Valley just south of Illinois. It is expected to
open up as it drifts eastward through the lower Ohio Valley this
morning. A few isolated light showers or storms will be
possible with this feature east of I-57 this morning, but most
of central Illinois is expected to stay dry today.

To the northwest, a cold front is dropping across portions of
the Upper Midwest and central Great Plains this morning. Ahead
of the front, a thermal ridge, with 850mb temperatures reaching
around 18C, will push into central Illinois. This will allow
temperatures to rebound this afternoon, with widespread highs
into the upper 80s, and a few spots touching 90.

As the front moves into and eventually stalls over the area on
Sunday, a sharp temperature gradient will form across the
region. Highs north of the Illinois River are projected to top
out in the mid 70s, whereas areas south of I-70 will warm to
around 90.

A prominent 700/750mb warm nose will keep deep surface based
convection capped Sunday, however, some light precipitation
still appears possible. Forcing is quite nebulous Sunday, but
weak isentropic ascent eventually develops along the 310-315K
surfaces resulting in mid level saturation that could produce a
few light showers or sprinkles. NBM mean 24-hour QPF for Sunday
generally shows up to a third of an inch in the west to 0.15
inches in the east.

     Monday through Wednesday...
An active, unsettled pattern is expected during the first half
of next week. A high-amplitude upper wave is forecast to move
from the Pacific Northwest across the Canadian Rockies Sunday
night into Monday. A deep surface low will develop in response
and track from the Canadian Prairies toward Hudson Bay Monday
into Tuesday.

An associated warm front will advance across the Great Plains
Sunday night, triggering nocturnal convection. Some of this
decaying activity could reach parts of west central Illinois as
the warm front shifts northward through the area on Monday.

A better chance for widespread showers and storms arrives
Tuesday into Wednesday as the trailing cold front moves into and
stalls over the state. This period will need to be monitored
for severe potential, as the upper-level jet extends into the
Great Lakes, increasing deep-layer shear along the stalled
front. Heavy rain will also be a concern with repeated rounds of
storms tracking east along the front. Through Wednesday night,
NBM mean QPF shows one inch along and north of a Beardstown to
Bloomington line with the two inch contour clipping our far
northwest forecast area near Galesburg.

     Thursday and Friday...
Unsettled conditions look to continue late next week as the
baroclinic zone remains draped across the Midwest, providing a
focus for daily rain chances. Guidance diverges on the precise
location of the boundary by Thursday and especially Friday.
Although specific timing and positioning details remain
uncertain, daily chances for showers and thunderstorms will
persist near the front. Temperatures will depend heavily on
where the front settles, but current guidance favors highs from
the 70s north of the front to the upper 80s or low 90s south.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 555 AM CDT Sat Sep 12 2026

An upper level disturbance over far southern Illinois will
bring some mid and high clouds to portions of east central
(DEC/CMI) IL early this morning. Light south winds will be in
place early this morning ahead of an approaching weak cold
front. Some patchy fog is possible for an hour or two after 18Z.
Winds will turn west today then northwest with passage of front
this evening, but should remain light through the period, at or
below 10 kt.

&&

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

&&

$$

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