textproduct: Central Illinois

KEY MESSAGES

- Flooding continues across portions of central IL in a corridor from Fulton and southern Knox County to Vermilion County due to 4 to 7 inches of rain that fell overnight.

- Additional clusters of thunderstorms are likely tonight into Sunday morning, with isolated afternoon thunderstorms possible Sunday afternoon. Storms have the potential to produce locally damaging winds. SPC has a marginal (level 1 of 5) risk of severe weather.

- The heat and humidity remain a concern this weekend, with the hottest conditions south of I-70.

DISCUSSION

Issued at 156 PM CDT Sat Aug 15 2026

In the wake of widespread thunderstorm activity this morning, heat has once again been tempered over much of the area with some late afternoon recovery expected to bring temperatures back up to the low 90s by afternoon in a corridor from Jacksonville to Robinson, with heat index likely to reach around 105 south of I-70 as a warm front lifts northward through the area. Mid to upper 80s can be expected to the north.

A few showers remain in this frontal zone, where perhaps a few thunderstorms could develop this afternoon as diurnal destabilization gradually takes place.

Tonight, a cold front will approach from the northwest, with warm advection ahead of the front promoting another cluster or two of thunderstorms. Areas of significant precipitation are possible, although much less likely than last night. The location of any heavy precipitation swaths remains too uncertain for a Flood Watch at this point, but we will continue to evaluate any corridors for potential Watch issuance. If expected heavy precipitation corridors line up well with last night's heavy precipitation from Fulton to Vermilion County these would be favorable for renewed flooding. 12Z high-res average model guidance points to a 1.5 to 1.5 inch corridor north of Peoria and Bloomington, although there remain considerable run-to-run and model-to-model discrepancies. SPC continues a Marginal Risk for locally damaging winds with thunderstorms both tonight and Sunday as these storms move across central IL and some afternoon thunderstorms as diurnal destabilization takes place and the cold front lingers over the southeast half of central IL.

A couple of dry days are forecast Monday and Tuesday behind Sunday's front, then another cold front midweek will bring the next chance for thunderstorms.

Temperatures will remain quite warm and humid for central IL as 2 inch precipitable water values keep dewpoints well into the 70s and highs reach the 80s, to lower 90s south of I-70. A Heat Advisory continues for areas south of I-70 until Sunday evening as heat index values will near 105 each afternoon until then. Highs will be in the 80s across the area Monday through Tuesday, then the midweek front will continue to lower temperatures for late in the week, with some upper 70s possible.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 617 PM CDT Sat Aug 15 2026

Another round of showers and thunderstorms is expected across central Illinois late this evening and overnight. Storms have started to redevelop over northern MO and southern IA early this evening and will gradually spread east across central Illinois tonight. A period of MVFR ceilings is favored at PIA/BMI at times this evening through Sunday morning. South winds in place today will set up out of the west to northwest Sunday.

ILX WATCHES/WARNINGS/ADVISORIES

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