textproduct: Central Illinois

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.

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 /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1213 AM CDT Tue Sep 15 2026

A warm front will lift through the area overnight, turning winds from southeasterly to southerly. Simultaneously, a 40-45 kt low- level jet is noted just west of the area and will bring a period of LLWS at KPIA and KBMI through early Tuesday morning. A cold front will approach from the west later in the day, sparking the development of scattered showers and storms. PROB30 groups are in place from 00-06Z which is when thunderstorm potential seems most likely. Outside of any storm activity, VFR conditions should prevail.

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.