textproduct: Central Illinois

KEY MESSAGES

- There is a diminishing threat of rain from the remnants of Isaias tonight into Sunday in our forecast area, with rain chances (20-30%) confined to a smaller portion of southeast Illinois.

- Near-record warmth arrives Monday, October 12, with afternoon high temperatures surging into the upper 80s to lower 90s. Tuesday looks equally as warm for our counties south of I-72. - An extended period of rain chances is on track Tuesday night through Thursday. Severe weather potential is uncertain but appears low at this point.

- Much colder air will arrive for the weekend of October 17-18, with our first approach toward patchy frost Saturday night and especially Sunday night.

DISCUSSION

Issued at 208 PM CDT Sat Oct 10 2026

The trend of lowering PoPs and QPF tonight into Sunday will continue with this update. The remnants of Hurricane Isaias are curving to the northeast sooner, and the westward expansion of the precip shield will only be into our CWA this evening, with dry air dissipating the precip potential. There is solid agreement in the CAMs on that scenario (HRRR, RAP, HREF, and RRFS). The primary forecast solution adopts a consensus blend of the HREF and HRRR, keeping low-end precipitation chances (2030%) restricted to far southeast Illinois while central Illinois remains dry.

Global deterministic models (GFS, ECMWF, ECMWF-AI) and their respective ensemble suites (GEFS, LREF) are in tight alignment regarding an unseasonably strong thermal ridge peaking on Monday, October 12 and now extending into Tuesday. NBM guidance indicates high confidence in high temperatures reaching 88F to 92F on Monday and that same temp range south of I-72 on Tuesday, which will challenge daily record highs across central Illinois climate sites.

For Tuesday night through Thursday, minor timing discrepancies exist between the GFS and ECMWF/ECMWF-AI. The GFS is slightly faster with cold front progression on Tuesday, whereas the ECMWF and ECMWF-AI hold the frontal zone nearly stationary parallel to upper-level southwesterly flow through Wednesday night. DESI LREF ensemble probabilities highlight a 6075% chance of cumulative rainfall exceeding 1.50 inches across central and east-central Illinois. Heavy rainfall potential is supported by PWAT values exceeding 1.6 inches (above the 90th percentile for mid-October). SPC convective outlooks, backed by CIPS and CSU machine learning severe probability guidance, indicate some risk for severe thunderstorms along and ahead of the boundary on Wednesday, but mainly just west of our CWA. WPC Excessive Rainfall Outlooks (ERO) highlight a Marginal to Slight Risk for flash flooding.

Following frontal passage Thursday night, a high-amplitude Canadian upper trough digs into the central and eastern United States. Ensemble guidance displays remarkable consistency regarding an unseasonably cold airmass intruding into the region. 850 mb temperatures drop into the -2C to -8C range by Saturday, October 17. That could support patchy frost developing in low lying areas Saturday night. A better chance for patchy frost looks to come next Sunday night.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1233 PM CDT Sat Oct 10 2026

VFR conditions are expected the upcoming 24 hours. Any mid-high clouds from the remnants of Isaias will remain VFR. CMI could see some lowering of the ceilings to 10K with some SCT060. Winds look to be S-SE at 6 to 10 kts this afternoon then weaken overnight with an easterly shift.

ILX WATCHES/WARNINGS/ADVISORIES

None.