textproduct: Central Illinois

KEY MESSAGES

- A Flood Watch continues for locations along and south of a Jacksonville...to Decatur...to Paris line through Saturday afternoon.

- The first prolonged heatwave of the summer will arrive next week when air temperatures rise into the 90s and maximum heat index values climb well above 100 degrees Sunday through at least Thursday.

DISCUSSION

Issued at 424 AM CDT Fri Jun 26 2026

*** Locally Heavy Rainfall ***

The rain event has so far underperformed as 08z/3am radar imagery continues to show just spotty showers across central Illinois. As a 40-45kt 850mb jet streak currently oriented from Texas northward to Kansas shifts toward southern Illinois, showers and thunderstorms will become more numerous as the morning progresses and will linger throughout the afternoon. Given precipitable water values increasing into the 2.00-2.25 range and forecast soundings indicating a deep warm layer, the showers will be efficient rain-producers. As a result, am expecting occasional downpours...particularly along/south of a Jacksonville...to Decatur...to Paris line where a Flood Watch will remain in effect. Storm total rainfall today through this evening will range from 1.50-2.50 across this area...with isolated higher amounts focused along/south of I-70 where a few strong storms will be possible late this afternoon. Further N/NW, rainfall amounts will decrease to less than 1 inch along/northwest of a Macomb to Bloomington line. The showers will linger into this evening, then will gradually dissipate/come to an end overnight.

*** Hot Weather Returns ***

After a few more showers/thunderstorms Saturday night, the highly advertised heatwave will commence across central Illinois on Sunday. As upper troughing digs west of the Rockies, pronounced downstream ridging will occur over the Midwest and Ohio River Valley. While there was initially some doubt concerning the exact strength/orientation of the ridge, model solutions have been consistently showing a dominant upper ridge centered over the region for much of next week. As upper heights rise, the persistent frontal boundary draped from the Ozarks into Kentucky will lift northward on Sunday...allowing afternoon high temperatures to climb into the upper 80s and lower 90s. While peak heat index readings may eclipse 100 degrees across the W/SW KILX CWA, the real heat and humidity will arrive on Monday...then persist through at least Thursday. Expect daily high temperatures in the lower to middle 90s with overnight lows in the middle 70s. With dewpoints hovering in the lower to middle 70s, heat index values will soar above 105 degrees.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 1217 AM CDT Fri Jun 26 2026

A warm front lifting through the area will stall out over central Illinois and promote scattered showers and storms through a good portion of the TAF period. Ceilings will quickly drop from MVFR to IFR by later this morning. Precipitation will come to an end by late afternoon or early evening, though probabilities are high that ceilings remain below 1k ft through Friday night especially at airfields closest to the front (KSPI-KDEC-KCMI).

ILX WATCHES/WARNINGS/ADVISORIES

Flood Watch through Saturday afternoon for ILZ049>057-061>063- 066>068-071>073.