textproduct: Central Illinois

KEY MESSAGES

- Occasional thunderstorms are expected the next few days. Some of these storms may be severe, with locally damaging winds, a few tornadoes possible, and isolated large hail.

- Dangerous heat remains a concern through the weekend, especially across southern portions of central IL, as afternoon heat index values approach 105 daily unless thunderstorm activity disrupts afternoon heating.

- A cold front arriving Sunday looks to bring relief from the heat for at least a few days by Monday.

DISCUSSION

Issued at 251 PM CDT Wed Aug 12 2026

Showers and a few thunderstorms remain over portions of central and southeast IL which resides in a relatively stationary frontal zone. With a complex of strong thunderstorms that pushed eastward along roughly the I-74 corridor this morning, an outflow pushed southward across much of the area with cooler air and cloud cover tempering instability across much of the area. However, SPC mesoanalysis indicates strong MLCAPE around 4000 J/KG lingering south of I-70. Another shortwave impulse currently initiating thunderstorms near western portions of I-72 is showing effective bulk shear of 40-50 kts and could drive another complex of severe storms as moves over that area this evening. SPC maintains a Slight Risk for severe storms in east-central and southeast IL, with damaging wind as the highest probability for severe weather (15% risk), but also a 2% tornado risk and 5% hail risk.

Tonight, most models have a relative lull in thunderstorm activity despite a few storms developing over the stalled frontal boundary, however another nocturnal MCS looks to be moving across IA overnight, heading toward northern or central IL Thursday morning. High-res ensembles depict 1000-200 J/kg MUCAPE overlapping 30-40 kt deep layer bulk shear and 100-200 SRH, and additional severe storms will be possible, for which SPC depicts a Marginal Risk. The pattern will continue through Friday if not Saturday as well.

On Sunday, a cold front will traverse the area driven by a more potent shortwave moving through the northern states. Additional showers and thunderstorms may accompany this frontal passage, then a quieter period should ensue for early next week.

Highs will range from 80s to lower 90s, with dewpoints well into the 70s, yielding afternoon heat index values approaching 105 daily for portions of central and southeast IL, especially southern portions. However, thunderstorm activity will greatly influence temperatures and heat index, and predictability of heat index remains low. Highs look to reach only into the 80s for early next week.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1243 PM CDT Wed Aug 12 2026

A corridor of scattered thunderstorms near a stationary frontal boundary will continue to bring chances for thunderstorms over the upcoming 24 hours. In the short term, a cluster of thunderstorms appears poised to sweep through the area from 18Z-23Z from NW to SE. Model guidance suggests relative inactivity of thunderstorms after that until 12Z-18Z as another thunderstorm complex propagates through the region. Conditions generally VFR outside of thunderstorms until around 07Z-10Z, then lowered cigs and vsby in BR, generally MVFR range. Winds generally light and variable, although localized winds influenced by shower and thunderstorm activity.

ILX WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 8 PM CDT this evening for ILZ066>068- 071>073.