textproduct: Central Illinois

KEY MESSAGES

- After lingering showers depart eastern Illinois this afternoon, the next chance of rain will be Tuesday night into Wednesday. There is a 50-70% chance of rain south of I-72/Danville, and a 30-50% chance to the north. Temperatures will generally be above normal this week, with highs in the low to mid 80s.

DISCUSSION

Issued at 119 PM CDT Sun May 24 2026

*** THROUGH TONIGHT ***

A weak cold front has pushed into Indiana as of late Sun morning, but lingering scattered showers continue in areas east of a Rantoul to Shelbyville line as of 1230pm/1730z. Shower activity was more widespread and persistent earlier this morning, with locally heavy amounts exceeding 1" in some spots near the I-55 corridor (north of Lincoln). The remaining precip activity is less expansive in coverage, and also more progressive as the associated system steadily shifts east. Thus, additional rainfall amounts seem unlikely to exceed 0.25" this afternoon, and this notion is supported by the morning HREF guidance. Latest observations show minimal lightning activity with the showers across eastern IL, but with MUCAPEs around 500 J/kg, a few rumbles of thunder can't be ruled out this afternoon. Precip should depart SE IL before sunset.

The only other forecast concern for tonight is the potential for fog development as weak sfc high pressure settles in, skies clear, and residual moisture persists in the low-levels. Latest high-res guidance did not change the footprint of the fog signal from previous forecasts, highlighting areas south of I-72/Danville and east of Decatur as being the most likely location for vis below 1 mile (20-30% chance). Given some of the heavier rains closer to I- 55, would not be surprised if the fog extended a bit further northwest than guidance is showing.

*** THIS WEEK ***

The upper pattern will be blocky this week, with a central US ridge gradually amplifying as an upper low becomes cut-off over the western US. The northeast will also feature troughing to some degree, setting up an Omega block of sorts that keeps the pattern slow to evolve this week.

Dry conditions are expected on Mon into Tues, as the frontal zone settles to the south of the ILX CWA. There is a weak upper disturbance present over the southern Plains currently, which guidance shows lifting towards the MO Bootheel by Tues eve. This will help tug the front northward, providing a rain chance Tues night into Wed, with chances higher south of I-72/Danville (50-70%) than to the north (30-50%). With both weak instability (MUCAPE less than 500 J/kg) and weak mid-level flow (500mb winds less than 25 kts), the prospects of severe storms is very low. PWAT values are progged to exceed 1.5", and forecast soundings/hodographs show a deep warm cloud layer (greater than 10kft) with cloud layer winds around 15 kts. This suggests at least some potential for slow- moving, efficient rainfall producing showers/storms. For comparison, today's showers that produced localized 1-2" totals were working with lower PWATs (1.2-1.5") and shallower warm cloud depths (less than 10 kft). For now, the coarser resolution global ensembles are not bullish about the heavy rain potential, showing just a 20-30% chance of over 1" south of I-70 through Thurs AM, with lower probs north of I-70. As a high-res guidance will likely provide a better idea of the localized, high-end rainfall amounts that could occur with this system.

For the latter half of the work week, sfc high pressure shifts south over the Great Lakes, helping to nudge the frontal boundary back to the south and introducing persistent E/NE flow that should advect drier air into the region. While the NBM keeps some broad (20-40%) PoPs in place across the SW half of the ILX CWA Thurs and Fri, precip chances on Thurs-Fri will be higher to the south/west of our area, maximized across far southern IL and into MO. The exact placement and strength of the high pressure system will impact just how much rain, if any, we see locally.

With upper ridging in place over the central CONUS for much of the week, temperatures will be running a bit above normal locally, with highs generally in the low to mid 80s.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1207 PM CDT Sun May 24 2026

Bulk of the MVFR ceilings have pushed east of the TAF sites at midday, though some diurnal cumulus development may result in some brief ceilings near 2000 feet from KDEC-KBMI east for a couple more hours. Otherwise, little aviation concerns for later this afternoon through Monday morning. Some of the high-res model guidance is suggesting some fog potential toward 10-12z at KDEC/KCMI. Ensemble probabilities of visibility below 5 miles is only in the 15-20% range, so will leave any mention out of this TAF set and continue to monitor the potential.

ILX WATCHES/WARNINGS/ADVISORIES

None.