textproduct: Central Illinois

KEY MESSAGES

- A heavy rain threat will persist through this evening, continuing into the overnight hours south of I-72/Danville. Rates of two inches per hour or greater may lead to localized flash flooding.

- The combination of heat and humidity will lead to heat index values peaking between 95 and 105 degrees on Tuesday and Wednesday. Those sensitive to heat should take extra precautions.

- The threat for severe weather will increase through this week, peaking in the late Wednesday night-Thursday time frame.

UPDATE

Issued at 935 PM CDT Mon Jun 8 2026

Made some tweeks to the pop/wx grids to better reflect radar trends for the rest of the night. Some of the new models are indicating chances of precip tomorrow in the east and central parts of the state, so made some adjustments for tomorrow as well. Additional showers are possible overnight, but chances are less than earlier forecasted. Update should have already gone out.

DISCUSSION

Issued at 241 PM CDT Mon Jun 8 2026

Near record precipitable water values of just over 2" along with an approaching upper low are driving a heavy rain threat today, with multiple reports of 2"/hour rain rates. East central IL will see the greatest threat for heavy rain over the next few hours. An MCV moving out of southeast MO may lead to thunderstorm development in portions of southeastern IL that have yet to see much activity. Some will see a brief break this afternoon, but with more showers/storms capable of heavy rainfall moving in from the west we anticipate the flood threat to persist through at least this evening. A few CAMs depict a convective complex with an associated MCV moving across MO and weakening during the overnight hours. The southern portion of the flood watch has been extended to 7 am to account for this possibility, as well as to account for the persistent near record PW values.

The combination of heat and humidity then become a concern for Tuesday and Wednesday. Heat index values in the mid 90s up to a few degrees over 100 are anticipated. Particularly following the extended period of dry and cool conditions experienced toward the end of May/in the first week of June, this period of heat and humidity could have more impact than usual. On Tuesday, a weak moisture boundary may trigger isolated thunderstorms but little relief from the heat will probably result. Instability is quite strong, but with shear limited the severe threat should be limited as well. The main concern would be isolated strong to severe wind gusts.

The severe weather threat is forecast to increase later in the week for central and southeast Illinois. Late Wednesday night into Thursday morning, severe storms coming out of the upper Mississippi Valley are forecast to weaken as they move toward central Illinois. The greater threat is anticipated on Thursday afternoon/evening, with SPC delineating a 30% contour approximately near and west of I-55.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1221 AM CDT Tue Jun 9 2026

Area of IFR ceilings extends from KGBG-KBMI northward this hour, with satellite data showing continued redevelopment along the southern edge. While KPIA/KBMI have seen breaks in the stratus at times, will go on the pessimistic side with the new TAF's and keep them IFR/LIFR the next few hours. Some additional development of ceilings below 3000 feet is anticipated over central Illinois, which is expected to persist a good part of the morning.

Development of new showers/storms is expected with some of the daytime heating, though coverage should be much less than on Monday. Currently focusing on the KSPI-KCMI corridor with PROB30 mentions, though an isolated shower/storm further north can't be ruled out.

ILX WATCHES/WARNINGS/ADVISORIES

Flood Watch until 1 AM CDT early this morning for ILZ027>031- 036>038-041>046-053-055-057. Flood Watch until 7 AM CDT this morning for ILZ040-047>052-054- 056-061>063-066>068-071>073.