textproduct: Central Illinois

KEY MESSAGES

- Oppressive heat and humidity continue through Monday with heat indices peaking between 100 and 110 degrees.

- Multiple thunderstorm complexes will move across the Midwest states through Monday, presenting a conditional threat for severe weather and heavy rain.

- A cold front will bring relief from the heat on Tuesday, transitioning us back to near-normal temperatures.

UPDATE

Issued at 904 PM CDT Sun Jul 26 2026

Updated PoPs to trim thunderstorm chances down for much of tonight given less activity than expected in the wake of a thunderstorm complex southeast of the area, despite several thousand MLCAPE still analyzed over the area by SPC Mesoanlysis product and effective bulk shear over 40 kts. Nevertheless, continued at least a slight chance for thunderstorms the next several hours in a band stretching from near Lawrenceville toward Quad Cities where anywhere from isolated to scattered radar returns have been noted northeast of the surface warm front. SPC continues a slight risk for severe thunderstorms over the area given the favorable parameters noted above.

DISCUSSION

Issued at 149 PM CDT Sun Jul 26 2026

Upper analysis shows a large ridge of high pressure over the west- central US with northwest flow over the Midwest states. At the surface, a stationary/warm front is positioned from roughly Burlington IA to Flora IL. Isentropic upglide on the ~300K surface has resulted in a consistent low stratus deck near/east of the boundary, ultimately holding temperatures down several degrees lower than originally anticipated. Clearer skies west of the front have allowed temperatures to surge into the upper 80s to low 90s, paired with dewpoints in the low 80s. Heat indices in these same areas have climbed above 100 degrees with Springfield and Jacksonville IL reporting heat indices over 110 degrees as of 1 pm. Although cloud cover looks to be slow to depart, any pockets of clearing should allow temperatures to quickly rebound. Because of this, no changes to our current heat products have been made.

Things remain hot and humid on Monday as the 850 mb ridge axis moves overhead, keeping 22-25C 850 mb temperatures largely in place. Monday has the potential to be the hottest day of the forecast period, pending any thunderstorm activity/convective debris clouds. Multiple thunderstorm complexes could impact parts of the region through Monday night as several upper shortwaves ride the eastern periphery of the upper ridge and a cold front approaches from the north. CAMs continue to struggle with thunderstorm placement and evolution, which has led to difficulty pinpointing timing. Water vapor imagery shows a subtle shortwave disturbance over eastern South Dakota/southern Minnesota with composite radar showing some storms ahead of that wave, potentially serving as our first opportunity for convective activity later this afternoon or evening. Additional waves are expected to track through the Midwest states overnight into Monday and could impact parts of the area. Any storms that do develop will have the potential to become severe as they move through an environment characterized by very strong instability (4000+ J/kg SBCAPE) and seasonally strong wind shear (30- 40 kts). Hazards with any severe storms would be damaging wind gusts in excess of 60 mph and torrential rainfall.

Temperatures and dewpoints drop closer to seasonal normals on Tuesday as the airmass modifies behind a cold front. Northwest flow will remain in place aloft through the upcoming week and may open the door for shortwave disturbances through next weekend. A brief window of surface high pressure should shield precipitation chances through midweek before a stronger upper wave approaches later in the week.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 638 PM CDT Sun Jul 26 2026

MVFR cigs from KDEC-KBMI eastward are expected to dissipate this evening, bringing a period of VFR conditions until lowered visibility in BR develops late tonight into Monday morning, for MVFR or worse vsby. Thunderstorms appear to be a low probability for much of the upcoming 24 hours, although there is potential for most of the period. The highest chances appear to be at KCMI around 12Z-16Z as a forecast storm complex from the north clips the area, and a PROB30 is in the KCMI TAF. Winds light and variable to S-SW around 5 kts tonight, becoming S 8-10 kts after 15Z.

ILX WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 9 PM CDT Monday for ILZ027>029-036- 037-040>042-047>052. Heat Advisory until 9 PM CDT Monday for ILZ030-031-038-043-044- 053-054-061-066-071-072.