textproduct: Central Illinois

KEY MESSAGES

- Spotty heavy rainfall through early evening creates a localized flash flooding threat across east central Illinois.

- Low-level horizontal shear along a trailing surface trough fosters brief funnel clouds across east-central Illinois through late afternoon.

- A late week weather system brings the next chance for showers and storms.

DISCUSSION

Issued at 150 PM CDT Sat Aug 1 2026

A vertically stacked/closed low slowly tracking east across central IL serves as the primary lifting mechanism for showers and isolated thunderstorms into tonight. Latest analysis depicts a moist airmass anchored beneath the low, with precipitable water (PWAT) values around 1.8 inches. The nose of modest instability (surface-based CAPE near 1000 J/kg) extends as far west as the IL/IN border. Within the zone of maximized ascent just north and east of the mid level low center over east central IL, localized rainfall rates up to 2 inches per hour are possible through early evening. A Flash Flood Watch remains in effect for east central IL through 06z, where localized totals of 2-5 inches have been seen in recent HRRR guidance.

Beneath the low and along the trailing surface trough axis in east- central Illinois, RAP and HRRR boundary-layer profiles show enhanced low-level vorticity, steep 0-3 km lapse rates where cloud breaks have developed, and minimal deep-layer shear. The Non-Supercell Tornado (NST) parameter highlights values of 1 to 2 across this area through 23z. These conditions favor brief, shear-zone funnel clouds - see latest Special Weather Statement (SPS) for more info.

Rainfall diminishes from the west tonight as the closed shifts eastward. Behind the low, MSLP gradient tightens, and will promote 20-30 mph wind gusts from the north-northeast through this evening. Post- frontal low stratus and patchy fog are likely to persist through daybreak Sunday. CAMs show isolated instability showers developing over eastern IL Sunday afternoon, and have 20-30% PoPs to cover this.

Ensemble and deterministic model suites are in strong agreement regarding transient upper-level ridging across the Mississippi Valley Mon-Tue. Dry weather prevails for this period with NBM guidance indicating seasonable high temperatures in the low-mid 80s.

Forecast guidance continues to show a mid-latitude shortwave trough digging out of the Northern Plains for the last half of the week. Notable model disagreements exist regarding the track and intensity of this feature, though the consensus show a front slowly moving in from the north, then possibly stalling. Resulting chance PoPs from the NBM extend from Wed-Fri. Generally weak shear should limit organized severe potential, with many ML/AI severe outlook products highlighting around a 5% risk for much the Fri-Sat periods.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 1214 AM CDT Sun Aug 2 2026

Isolated -shra will continue southeast of KPIA until 08Z-12Z, along with IFR-MVFR cigs and spotty MVFR vsby. Thereafter, cigs will gradually improve, although remaining generally MVFR through 17Z-22Z. Winds NNE 10-15 kts with gusts 18-24 kts, diminishing to 5-10 kts by 01Z.

ILX WATCHES/WARNINGS/ADVISORIES

None.