textproduct: Central Illinois

KEY MESSAGES

- A few showers and thunderstorms will develop north of the I-70 corridor this evening. Severe weather is not expected.

- A storm system will spread widespread showers and thunderstorms into central Illinois Thursday night into Friday. At this time, it appears the risk for severe weather will remain low (less than a 15% chance).

DISCUSSION

Issued at 244 PM CDT Tue Apr 21 2026

*** A Few Showers and Thunderstorms Tonight ***

A weak cold front analyzed on the 18z/1pm surface chart extending from northern Michigan to northern Iowa will sag southward this evening...triggering a few showers and thunderstorms across mainly north-central Illinois. Given limited low-level moisture return as evidenced by current surface dewpoints only in the lower to middle 50s immediately ahead of the boundary, think areal coverage of precip will remain low. Most CAMs continue to focus most of the activity further upstream across southern Michigan/northern Indiana where convergence along the front will be stronger. Further W/SW across the KILX CWA, think 20-40 PoPs will suffice. Latest satellite imagery shows high-based convection developing from north of LaSalle/Peru northeastward into the Chicago metro. Given bases of 6000-8000ft and a pronounced dry sub-cloud layer, a few of the cells could potentially yield brief wind gusts of 40-50mph: however, the risk for severe weather is virtually nil.

*** Higher Risk for Thunderstorms Thursday Night into Friday ***

After a period of warm/dry weather Wednesday and Thursday, the next significant storm system will push into the region by the end of the week. While minor timing discrepancies exist, both the 12z GFS and ECMWF suggest the associated cold front will swing through central Illinois around midday Friday. Favorable instability/shear parameters will be in place ahead of the system across the Plains late Thursday, resulting in a 15-30% chance for severe weather along/west of a Des Moines, Iowa to Tulsa, Oklahoma line. Some of this activity will spill eastward into central Illinois in a weakening state Thursday night into Friday morning. Diurnal de-stabilization will be greatest from the Ozarks southward into the lower Mississippi River Valley by Friday afternoon/evening. So while the local severe weather risk is non-zero on Friday, the highest probabilities (15-30% chance) will be focused from southern Missouri southward to Louisiana/east Texas.

*** Dry Weekend Ahead ***

As the cold front drops southward into the Ohio River Valley, a slightly cooler/drier airmass will settle into central Illinois this weekend. High temperatures both Saturday and Sunday will top out in the lower to middle 70s while overnight lows dip into the upper 40s and lower 50s. After a pleasant weekend, the next approaching short-wave trough will help push the prevailing frontal boundary back northward by early next week, resulting in likely PoPs (60% or greater) late Sunday night into Monday. While the most unstable airmass will remain to the south of Illinois from the lower Ohio River Valley southward, will need to keep an eye on the potential for severe weather. While it is still too early to discuss specific risks/timing, both the NCAR and NSSL severe weather algorithms suggest a greater than 15% chance for severe at least as far north as the I-70 corridor on Monday. Stay tuned to later forecasts for more details.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 611 PM CDT Tue Apr 21 2026

Weak band of showers has been pushing southeast, but thunder potential has been waning and will only mention a VCSH for the next couple hours at all sites except KPIA. While VFR conditions are expected to prevail through Wednesday, some of the guidance has been hinting at some potential MVFR ceilings from KPIA-KCMI between about 12-16z. Probability of this occurring is about 30-40% at this time.

ILX WATCHES/WARNINGS/ADVISORIES

None.