textproduct: Central Illinois

KEY MESSAGES

- WPC has a slight risk excessive rainfall outlook today for areas east of I-55 and north of I-70. Flash flooding could occur where grounds are already saturated or after multiple rounds of heavy rain over the same locations. Expect rainfall totals of 1.5 to 3.0 inches in these persistent bands, with significantly lower amounts elsewhere.

- Outside of thunderstorms, winds will be quite gusty from the tightening pressure gradient today. The HREF shows a 60-80% chance of wind gusts greater than 35 mph west of I-55 during the afternoon and evening hours.

- Pleasant, dry, and warm weather follows for Monday and Tuesday, before rain chances return mid-to-late next week. Confidence in the late-week timing remains low, so please check back for later forecasts.

UPDATE

Issued at 920 AM CDT Sat Aug 1 2026

Vertically stacked low pressure system was centered over west- central IL this morning. Regional radar mosaic indicated scattered showers pinwheeling around the low, with the highest coverage over central and northern IL. Thermodynamic profiles reflect weak mid-level lapse rates but substantial low- level moisture. Precipitable water (PWAT) values near 1.6 inches will nourish slow- moving convective showers and a few isolated thunderstorms today. The highest convective intensity focuses over east- central Illinois, where HRRR and HREF guidance indicates hourly rainfall rates up to 2-3 inches. Given these rain rates, ponding on roadways and localized flash flooding in low- lying or urban areas remain a risk through early this evening. NAM/RAP surface vorticity and non- supercell tornado (NST) parameter fields depict values between 1 and 2 coincident with the core of the low pressure system, particularly near and south of I-72 this afternoon. Surface based instability will depend heavily on solar insolation; if cloud breaks develop this afternoon, localized stretching will elevate the risk for shear-zone funnel clouds.

DISCUSSION

Issued at 201 AM CDT Sat Aug 1 2026

A low pressure system is slowly traveling through the central part of the United States. Showers and thunderstorms will push through central and southeastern IL again today, but won't be a complete washout as there will be breaks in the rainfall. The next round of showers and storms will develop later this morning as the low pivots into the area. Coverage will be scattered. Outside of any storms, skies will be cloudy. The greatest rainfall amounts won't be widespread and will be fairly localized. As of this morning, MRMS is estimating some localized pockets of 1-2 inches across central and southeastern IL in the last 24 hours. In contrast, some locations have seen less than a quarter inch in that same time period. WPC has us in a slight risk ERO for today for areas east of I-55 and north of I-70. Flash flooding could occur where grounds are already saturated or after multiple rounds of heavy rain over the same locations.

As the low pressure center moves directly overhead throughout the day, the non-supercell tornado parameter will increase as localized maximums of low-level SRH pivot over the central part of the state. Someone may see a funnel cloud (or multiple) across central IL. Outside of thunderstorms, winds will be quite gusty from the tightening pressure gradient. The HREF shows a 60-80% chance of wind gusts greater than 35 mph west of I-55 during the afternoon and evening hours.

Temperatures will be unseasonably cool with highs in the 70s today. Temperatures gradually increase solidly back into the 80s by midweek next week. Lows will be in the 60s for the next week before warming into the 70s by Friday night. Weather will dry out for Monday and Tuesday, but additional rain chances muddle the new week starting Wednesday. There are low (~20%) chance for showers and thunderstorms off and on throughout next week from the timing uncertainty of when an upper level shortwave will push into Illinois, dragging a cold front along with it.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1222 PM CDT Sat Aug 1 2026

Low pressure was centered near KDEC at 17z. North of the low, widespread showers and IFR ceilings were prevalent at KPIA-KBMI. South/east of the low, spotty showers and SCT-BKN IFR stratus was prevalent at the other central IL terminals. As the low tracks east this afternoon, IFR conditions are expected to expand over the remainder of the terminals. SHRA will diminish from the west late afternoon to early evening, coincident with a tightening pressure gradient on the back side of the low. This will result in N/NE gusts increasing to 20-25 kt. The gusts may subside for a time later tonight, then return after sunrise. IFR ceilings will be prevalent into Sunday morning, with higher probabilities of MVFR ceilings west of I-55 by late morning.

ILX WATCHES/WARNINGS/ADVISORIES

Flood Watch through late tonight for ILZ045-046-055-057.