textproduct: Central Illinois

KEY MESSAGES

- There is a low (5-15%) chance for localized flash flooding tonight due to additional heavy rainfall.

- The severe weather potential is increasing for Thursday, primarily between 4pm and 9pm. Tornadoes and damaging thunderstorm winds are the primary hazards.

- Gusty, non- thunderstorm winds will grip the region on Thursday. Occasional gusts between 30-50 mph are likely, posing a risk to high-profile vehicles traveling along east- west highways.

DISCUSSION

Issued at 401 PM CDT Wed Apr 1 2026

This afternoon marks a brief return to drier and cooler conditions as an elongated surface high-pressure system quickly moves across the region under rising mid-level heights. Temperatures have dropped significantly, nearly 30 degrees behind the front, resulting in afternoon highs in the upper 40s areawide.

Another round of showers and thunderstorms is expected tonight into Thursday as a robust shortwave trough moves over the central U.S. Locally heavy rainfall is possible, mainly focused near and north of the Illinois River Valley, where 0.75"-2" is forecast based on the latest HREF LPMM QPF guidance. Activity will blossom along and north of a lifting warm front. The necessary lift, moisture, and forcing will be provided by a strong low-level jet overrunning this surface boundary, combined with subtle shortwave energy rippling-in parallel to the boundary, supporting another round of locally heavy rain closer to the surface low.

The risk of severe weather then looms for Thursday with central Illinois positioned well within the warm sector, ahead of an advancing dry line. Temperatures and dewpoints will surge on the nose of gusty southerly winds with afternoon highs pushing well into the 70s and dewpoints into the 60s. Partial sunshine should support deep boundary mixing in areas east of the Illinois River Valley, within occasional gusts up to 50 mph. A wind advisory is now in effect for a good chunk of Thursday to cover this non-thunderstorm wind threat.

The tornado potential, specifically, remains somewhat uncertain. Favorable conditions for supercell and multicell cluster development exist: an incoming 500-mb speed maximum pushing deep layer shear into the 40-50 kt range, and ample buoyancy across the warm sector (1500 J/kg). Furthermore, a strong LLJ of 50-60 kts will veer in, supporting elongated hodographs conducive to robust low-level spin.

Despite these factors, two elements may limit tornado production during the afternoon: relatively high LCLs and the fact that the better Storm Relative Helicity (SRH) is expected to be displaced over parts of northern Illinois and southern Wisconsin. Consequently, the highest tornado risk may be delayed until the evening hours, directly along the dry line as it moves across central Illinois.

Global forecast models continue to indicate a significant upper- level trough and frontal system approaching by Friday evening, likely bringing another round of showers and thunderstorms. The current expectation is for a decaying line of storms to enter west-central Illinois late Friday night, perhaps washing out Saturday morning before convection redevelops along it Saturday afternoon across the eastern third of Illinois. Severe weather may accompany this frontal passage as well, with the SPC currently outlining central Illinois in a Marginal Risk (Level 1 of 5) for Friday night.

Following the weekend system, drier and seasonably cooler weather is strongly anticipated starting Sunday. This is due to a persistent upper-level ridge that will develop across the western CONUS, resulting in high pressure dominating our area.

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

Issued at 613 PM CDT Wed Apr 1 2026

IFR ceilings and MVFR visibilities will be common tonight, ahead of a warm front advancing north from southern IL. After the front passes Wed morning, ceilings should rise to MVFR, then VFR a few hours later. Winds will be gusty through the forecast, initially northeast this evening, then southeast Wed morning, and S-SSW by midday. The highest gusts should occur midday through afternoon, near 40 kt at times. A few periods of TSRA are likely, though timing at a particular terminal is low confidence at this point. The better chances of storms tonight will be west of I-55, where a PROB30 was included at KPIA- KSPI- KBMI. Another round of storms is forecast Wed afternoon and introduced a TEMPO TSRA group area-wide.

ILX WATCHES/WARNINGS/ADVISORIES

Wind Advisory from 10 AM to 6 PM CDT Thursday for ILZ038- 042>046-051>057-061>063-067-068.