textproduct: Central Illinois

KEY MESSAGES

- Heat indices will top out around 100 degrees this afternoon south of I-72 due to high temperatures in the 90s and rising humidity levels.

- Scattered thunderstorms this morning and afternoon, becoming more widespread late tonight along a stalled front; localized heavy rainfall of 1 to 3 inches could cause localized flooding, particularly south of I-70. There is a marginal risk (level 1 of 5) for severe thunderstorms near/south of 1- 72.

DISCUSSION

Issued at 205 AM CDT Wed Sep 9 2026

Moisture transport will increase today bringing soupy dewpoints in the 70s into the central part of the state. Heat indices will be greatest the further south you travel in the state, with 95+ degree heat indices south of I-72. However, there could be some limitations with the how high the heat indices may reach with the cloud cover from convective debris across the state and how fast the cold front today may move through. Currently, the front is located across central Iowa, extending north to northern Ontario.

The cold front will clear out the sweltering mid to upper 90 temperatures, leaving highs in the low to mid 80s before building back to upper 80s to low 90s this weekend into early next week. The LREF suggests that there is a 40-70% chance of high temperatures cooler than 80 degrees by next Tuesday north of I-72.

Showers and thunderstorms will move through today as the front pushes south and eventually stalls out across the southern half of the state overnight. At the moment, there is an area of convection moving east across the northern half of the state, scraping our northern most counties early this morning. This initial area of convection will begin to push south as morning progresses and widely dry out late this morning into the afternoon hours. Scattered activity will remain during the afternoon as the front pushes southeast through the state. This storms could have strong to damaging winds within the strongest storms/clusters.

Redevelopment may begin later than previous forecasts, as the CAMs have the area of new convection moving into the southeast around 06z tonight. This convection looks to train near and south of I-72 along the stalled front as the LLJ increases. The heaviest rain may be along and south of the I-70 corridor. Another scenario that could occur, is that this redevelopment doesn't happen or is not nearly as widespread, as depicted by the RRFS 09.00z run. Say the more widespread redevelopment with heavy rain scenario plays out, it would continue into Thursday morning and potentially have a low risk for flash flooding, rather than severe threat. However, this area can likely take quite a bit of rain before flooding becomes a major concern. The 6 hour FFG for the southeast is 3-5 inches. PWATs in that area are forecast to be 2.0-2.5 inches so very heavy rain is possible. Localized swaths of 1 to 3 inches are possible (particularly along and south of I-70) as highlighted by the HREF LPMM.

WPC has maintained a D2 marginal risk ERO along/south of I-72. SPC has shrunk the D2 marginal risk for severe weather near/south of 1- 72. Damaging winds are the most likely hazard with the strongest storms.

Additional low-end chances exist for showers and thunderstorms through the weekend. Due to low predictability and model spread, broad-brushed 20-40% PoPs remain in place from Friday night through early next week.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1219 AM CDT Wed Sep 9 2026

Cluster of thunderstorms along the IL/IA border currently on a trajectory to pass north of KPIA, though additional development is expected toward daybreak as a cold front begins to move into central Illinois. Best chances of thunder will be at KPIA/KBMI through mid morning, though southern extent of the rain shield is more questionable and it is uncertain whether the rain will reach KDEC/KSPI. Winds do turn around to the northwest at all sites during the morning with frontal passage, though drop off in speed toward 00z.

VFR conditions expected to prevail with ceilings generally at or above 10kft, though some lower ceilings closer to 4000 feet will accompany any thunderstorms.

ILX WATCHES/WARNINGS/ADVISORIES

None.