369
FXUS63 KILX 151539
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1039 AM CDT Tue Sep 15 2026

.KEY MESSAGES...

- Showers and thunderstorms will track across central Illinois
  today. For this afternoon and evening, there is a marginal
  risk (level 1 of 5) that a few storms could produce isolated
  damaging wind gusts.

- Repeated heavy rainfall today and Wednesday will bring 0.5 to
  1.5 inches of rain across most of the area, with isolated
  swaths of 2 to 3 inches possible near and north of the
  Illinois River.

- Hot and humid conditions today will drive afternoon heat
  indices near 100 degrees, primarily along and south of
  I-72/Danville. Expect an 80-90% chance of high temperatures
  reaching at least 95 degrees in these southern areas.

&&

.UPDATE...
Issued at 1038 AM CDT Tue Sep 15 2026

Showers have been increasing recently from the southeast corner
of Iowa to near La Salle, where surface analysis shows an
outflow boundary from the overnight convection across northern
Illinois. Latest mesoanalysis shows this area is still somewhat
capped, but by early afternoon, RAP guidance shows an axis of
1500-2500 J/kg CAPE over west central Illinois to just north of
Bloomington. Several of the morning high-res models show
additional development between the Illinois River and I-72, with
additional waves of showers/storms later this evening and
overnight in this same general area. Some updates to the PoP`s
have been made through tonight for the latest trends.

Still also watching heat trends south of the boundary today. Dew
points in the mid-upper 60s continue near and south of I-70.
Highest dew points today are expected over the northern CWA with
moisture pooling along the boundary. Heat index values of
100-105 degrees are still likely near and south of I-72, just
below advisory levels.


&&

.DISCUSSION...
Issued at 147 AM CDT Tue Sep 15 2026

Early this morning, low pressure is centered near the
Manitoba/Ontario border with a cold front stretching south
across Minnesota into Iowa. A corridor of strong warm air
advection well ahead of the front is driving an ongoing line of
showers and thunderstorms. This activity will generally shift to
the northeast within the southwesterly flow, with some eastward
propagation bringing precipitation chances close to or just
into portions of the Illinois River Valley during the predawn
and early morning hours.

The front is expected to push into central Illinois this
afternoon and stall across the region through mid to late week
as it lays out parallel to the upper-level flow. Widespread
showers and thunderstorms will accompany the front today and
Wednesday, bringing localized severe weather and heavy rainfall
risks. Unsettled weather and high humidity will persist through
late week.

The parameter space will be favorable to support a few severe
storms this afternoon and evening. As the frontal boundary
settles over central Illinois this afternoon, diurnal heating
will produce modest instability ahead of the front, with MLCAPE
increasing to 10001500 J/kg. Meanwhile, deep-layer shear of
3040 kt, driven by an upper-level jet streak over the Upper
Midwest, will intersect the stalled boundary. CSU machine
learning continues to paint a swath of severe wind probabilities
of 1530% across much of central Illinois. SPC maintains a
Marginal Risk (level 1 of 5) for severe thunderstorms today.

Hydro concerns persist as steering flow becomes quasi-parallel
to the frontal zone, setting up convective training. HREF mean
QPF through Wednesday evening indicates that much of central
Illinois north of I-72 and south of I-70 could see between
0.5-1.5 inches of rainfall. HREF LPMM, meanwhile, indicates a
few isolated swaths of 2-3 inches will be possible, especially
near and north of the Illinois River.

Temperatures are expected to warm well into the 90s across most
of central and southeast Illinois east of the Illinois River.
Temperatures south of I-72/Danville have around an 8090% chance
of reaching or exceeding 95 degrees this afternoon per NBM. Dew
points in the 50s this morning will be replaced by low to
mid-70 dew points this afternoon. This will result in triple-
digit heat indices this afternoon, especially along and south of
I-72/Danville. We may flirt with reaching Heat Advisory
criteria (105F), but confidence in this occurring on a
widespread basis is currently low and precludes extending heat
headlines further north into central Illinois at this time.

A sharp thermal gradient will be in place over central Illinois
across the frontal boundary starting Wednesday. Highs north of
the front will remain in the upper 70s to mid-80s, while areas
to the south reach the low to mid-90s with dew points climbing
into the lower 70s.

Thursday through Saturday: The overall synoptic pattern is slow
to change through the end of the week into the weekend. A
strong upper-level high will remain anchored over the
southeastern CONUS with ridging extending across the Midwest.
The surface frontal boundary will waffle over the region but
remain in our general area, providing daily precipitation
chances along with a sharp north-to-south temperature contrast
across the front. Temperatures in the 90s remain favored across
southern portions of the forecast area, with mid-80s in the
north.

Sunday through Tuesday: The upper ridge is progged to weaken
late in the weekend into early next week. To our west, a closed
upper low will track east across the northern Great Plains into
the Upper Midwest. Another round of showers and thunderstorms
will accompany this wave Sunday, but precipitation chances and
90-degree temperatures will eventually settle south of the area
by Monday and Tuesday as a cooler air mass filters into the
region in its wake.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 556 AM CDT Tue Sep 15 2026

Early this morning, a cold front stretches from northern WI
southwest into Iowa. A line of thunderstorms is ongoing well
ahead of the front. While the line is favored to stay just north
of the terminals this morning, though it may get near PIA and
bears watching. Otherwise, scattered showers and thunderstorms
will redevelop along the cold front this afternoon and evening
as the front settles across central Illinois. S/SW winds ahead
of the front will become light and variable within the frontal
trough, then favor a northeasterly direction behind the front.

&&

.CLIMATE...
Issued at 220 PM CDT Mon Sep 14 2026

Record temperatures the next several days:

Location         Tue        Wed       Thu       Fri       Sat
========       ========  ========   =======   =======   =======
Bloomington    102/1939   98/1939   97/1927   97/1906   95/1948
Champaign       98/1939   98/1939   94/2018   97/1893   94/1948
Charleston      99/1939   98/1927   98/1927   97/1954   96/1925
Decatur        101/1939   99/1939   97/1954   96/1983   97/1955
Jacksonville   101/1939   97/1939   97/1927   95/1955   96/1925
Olney          104/1939  100/1927   99/1927   99/1953   98/1940
Peoria         100/1939   94/1939   95/1927   93/1908   95/1948
Springfield    100/1939  100/1939   95/1954   95/2018   95/1978

&&

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

&&

$$

KEY MESSAGES...Deubelbeiss
UPDATE...Geelhart
DISCUSSION...Deubelbeiss
AVIATION...Deubelbeiss
CLIMATE...Geelhart