Area Forecast Discussion

KEY MESSAGES

- Light to moderate showers will track across central Illinois through Sunday, bringing beneficial rainfall with little to no flooding impacts. Chances of exceeding an inch over the weekend is under 10% areawide.

- Daily rain chances and mild temps with highs in the upper 60s and 70s continue into the first half of next week, with a 60% chance for rainfall to exceed one inch west of I-57 by Wednesday night.

- A cold front will pass through the region Wednesday night into Thursday, bringing blustery north winds and dropping daytime temperatures back into the 50s and possibly 40s in spots.

UPDATE

Issued at 741 PM CDT Fri Oct 30 2026

Showers have been persistent from southeast Iowa to about Peoria, then into east central Illinois. Overall, high-res models have been struggling with this activity, but this appears to be lined up with an 850-700 mb theta-e gradient seen in the latest RAP guidance. This gradient is expected to pivot northeast through the night, with rain chances becoming highest closer to the I-80 corridor by 3-4 am. While the forecast has been updated a couple times for current rain trends, some more substantial updates across the northern CWA will be made soon to hit the rain chances harder.

DISCUSSION

Issued at 128 PM CDT Fri Oct 30 2026

NEAR TERM /THROUGH TONIGHT/... This afternoon, a broad surface high stretches from the Canadian Prairies into the Great Lakes. Isentropic ascent and mid-level warm air advection west of the ridge axis will drive showers and a few storms with the initial focus across northern Missouri into Iowa and west central Illinois early this afternoon, but spreading east across portions of central and east central Illinois through the remainder of the day. Weak elevated instability rooted near 800 mb will support shallow convection; however, poor mid-level lapse rates will keep equilibrium levels near or below the ice-growth zone, suppressing lightning potential. HREF LPMM shows the potential for localized rainfall swaths of 0.50 to 1.00 inch, especially northwest of the Illinois River Valley, but rainfall amounts will taper quickly further east with little to no measurable precip expected east of I-55.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Broad isentropic ascent across the 300-315K surfaces will further expand east across the Mississippi Valley over the weekend, bringing additional rain showers Saturday and Sunday. Weak mid-level lapse rates (<6.0 C/km) will continue to limit thunderstorm activity, but moisture transport will push precipitable water (PWAT) values up to 1.00-1.30 inches by Sunday afternoon--exceeding the 90th percentile of GEFS model climatology. NBM 48-hour mean QPF values average around 0.10 to 0.25 inches through Sunday night. NBM 90th percentile has trended down but still suggests isolated pockets exceeding 0.5-0.75 inches will be possible over the weekend. NBM probability for exceeding an inch is now less than 10% across the forecast area for the weekend. Given the antecedent dry conditions, any rainfall will be beneficial with negligible impacts.

LONG TERM /MONDAY THROUGH FRIDAY/... A closed upper-level low over the West Coast this weekend will dig southeastward across the Intermountain West Sunday night into the Central and Southern Plains Monday, inducing surface cyclogenesis over Colorado and Kansas. The upper low is projected to stall and slowly meander eastward across the mid/lower Mississippi Valley through midweek, ejecting several lobes of vorticity ahead of this feature and supporting daily chances for showers and a few storms through at least the first half of next week. NBM probabilities for reaching at least an inch of rain in 48-hours peak around 60% west of I-57 Wednesday evening/night. Mild temperatures in the upper 60s and 70s will dominate early to midweek.

Timing differences between the models persist but are starting to hone in on the surface low and attendant cold front passing through central Illinois Wednesday night into Thursday. High temperatures drop into the 40s and 50s in the wake of the system under a period of blustery northerly winds. Given the continued timing discrepancies among models, the NBM currently broad- brushes the thermal gradient late in the week averaging out the forecast highs in the 60s.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

Issued at 615 PM CDT Fri Oct 30 2026

Scattered showers will continue moving across central Illinois early this evening, but with time, will become more concentrated just north of KPIA. Have seen some brief drops in visibility to 2-3SM, though this occurrence has been becoming less frequent. Overall, ceilings are expected to be in the 10kft vicinity through Saturday afternoon. Northeast winds of 8-10 knots will gradually trend more toward the east-southeast through the period.

ILX WATCHES / WARNINGS / ADVISORIES

None.