textproduct: Central Illinois

KEY MESSAGES

- After a brief respite, temperatures will again run well above normal the remainder of the week. Per LREF ensembles, probabilities of high temperatures above 95 degrees are generally 40-60% in areas south of I-70 through the upcoming weekend.

- An incoming cold front will stall over central Illinois, with periods of showers and thunderstorms Tuesday and Wednesday. There is a low (5-15%) probability of damaging winds with the storms Tuesday afternoon and evening.

DISCUSSION

Issued at 220 PM CDT Mon Sep 14 2026

Dew point temperatures this afternoon are only in the mid 40s to lower 50s across the forecast area. However, as southerly winds increase overnight, a fetch of Gulf moisture will bring them up into the mid 60s over west central Illinois by daybreak. Ahead of the incoming cold front, this juicier air mass will overspread central Illinois on Tuesday. As temperatures over much of the area reach well into the 90s, triple digit heat indices will return to areas near and south of I-72. There remains a concern with needing a heat advisory, but at the present time, the highest dew points will be closest to the front, where temperatures should only reach the 80s. With the front stalling over central Illinois, highs in the 90s will continue south of it the remainder of the week. ECMWF Extreme Forecast Index is near the top of the scale through Thursday. Temperatures may fall just shy of records, but will be close in some instances (see table in Climate section below).

Mixed layer CAPE's over the forecast area are progged to reach 2000-2500 J/kg on Tuesday, with decent 0-6km shear around 30-40 knots immediately along the front. Several of the CAM's are showing development near the I-72 corridor toward mid to late afternoon, though just south of the axis of highest shear. SPC Day2 convective outlook hasn't changed too much, still highlighting a level 1 risk of severe weather over nearly the entire forecast area. Periods of shower/storms continue through mid week, though they will shift northward with time as the front begins to lift back north.

As we get into the weekend and early next week, persist upper level high pressure over the lower Mississippi Valley should finally shift eastward, allowing for some cooler weather to arrive by Monday. However, the international models are suggesting ridging redeveloping over the Plains early next week, edging eastward. with a warming trend. CPC outlook for September 20-24th indicates a 50-60% chance of above normal temperatures to start autumn.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1211 PM CDT Mon Sep 14 2026

VFR conditions to prevail the next 24 hours, with most clouds of the higher variety until early Tuesday morning. At that point, scattered clouds around 3-4kft are expected with a dissipating line of convection ahead of a cold front moving in from the northwest. Will only mention a PROB30 for KPIA at this point, as most guidance significantly fizzles out the showers east and southeast of there.

A low level jet is still expected to develop across eastern Iowa and northern Missouri this evening, edging eastward as the front approaches. Conditions become more borderline toward KDEC/KCMI, but will continue a mention of LLWS further west. Other than that, southeast winds will gradually trend more south-southwest by early Tuesday morning ahead of the front, with speeds of 10 knots or higher common.

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.