textproduct: Central Illinois

KEY MESSAGES

- An Extreme Heat Warning remains in effect areawide through Friday and for parts of the area Saturday with dangerous heat index values between 100 and 109 degrees. - There is a very low chance (10-15%) for an isolated severe thunderstorm late this afternoon and evening and again Friday afternoon and evening. The primary threat will be damaging wind gusts. A marginal severe risk lingers over portions of east central Illinois Saturday.

DISCUSSION

Issued at 142 PM CDT Thu Sep 3 2026

Excessive Heat A robust 595 dam 500mb ridge remains anchored over the southern Appalachians, with ridging extending across central Illinois into the Upper Midwest. The 12Z KILX sounding sampled 850mb temperatures just above 22C, well above the 90th percentile (18.6C) for early September climatology. This pattern continues to drive the ongoing heat wave, with heat indices consistently ranging between 100-109F over the past couple days. An Extreme Heat Warning remains in effect areawide through Friday. Modest relief is expected by Saturday as the upper ridge retrogrades, though the Extreme Heat Warning will be maintained for the southern tier or two of counties (roughly Rushville to Robinson south) where peak indices will linger near 105F.

Convective Risk and Severe Potential The region remains on the periphery of the upper ridge, where a Ring of Fire pattern persists. An outflow boundary from earlier convection across far northern Illinois has drifted into portions of central Illinois, potentially focusing isolated development late this afternoon or evening. While a stout 650mb warm nose currently acts as a capping mechanism, localized forcing from the outflow could allow for convective initiation. Where surface-based instability can overcome the cap, progged MLCAPE values of 3000 J/kg and deep-layer shear of 25-35kt could support isolated supercell structures, though weak low-level shear and marginal LCL heights suggest the tornado threat remains negligible.

Heading into Friday, the focus shifts to convective outflow from an MCS potentially traversing the Upper Midwest into the southern Great Lakes. Should an outflow boundary reach the local area, pulse-severe storms are possible in an environment of high instability (>3000 J/kg) and weak shear (15-20kt), with damaging wind gusts serving as the primary hazard.

Extended Outlook A transition in the synoptic pattern is anticipated this weekend as the upper ridge axis retrogrades toward the central Great Plains, amplifying as an upper trough digs across the Canadian Maritimes and New England forming an Omega Block. This will shift central Illinois into a northwest flow regime by early this weekend. An 850mb baroclinic zone will straddle the region, with a backdoor cold front providing a modest cooling trend in northeast Illinois; temperatures will drop from the 90s into the mid-to- upper 80s Sunday and Monday for parts of the area that see frontal passage. Further south, an Extreme Heat Warning remains in effect. This reprieve in our northeast counties will be short-lived, however, as the ridge axis builds back east early next week, supporting a return of widespread 90-degree heat by Tuesday and Wednesday.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1206 PM CDT Thu Sep 3 2026

The Central Illinois terminals will remain between high pressure over the southeast CONUS and a stationary front over the Upper Midwest. South to southwest flow will continue across the area as a result. SW winds around 10 kt during the day will drop off below 10 kt and back to southerly after sunset. Some mid level clouds are expected but VFR conditions will prevail through the period. There is a very low but non-zero chance (around 10-15%) late this afternoon and early evening for an isolated pop-up storm over the area.

CLIMATE

Issued at 440 PM CDT Mon Aug 31 2026

Record high temperatures this week:

Location Thu 9/3 Fri 9/4 ======== ======== ======== Bloomington... 102/1913 100/1925 Champaign..... 99/2011 100/1954 Charleston.... 100/1925 98/1925 Danville...... 99/1913 101/1954 Decatur....... 102/1913 103/1913 Jacksonville.. 101/2011 103/1899 Lincoln....... 100/1913 102/1954 Olney......... 105/1925 103/1954 Paris......... 101/1913 104/1954 Peoria........ 99/1913 98/2015 Springfield... 100/2011 100/1954

ILX WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 7 PM CDT Friday for ILZ027>031- 036>038-041>046-053>057-063. Extreme Heat Warning until 7 PM CDT Saturday for ILZ040- 047>052-061-062-066>068-071>073.