textproduct: Central Illinois

KEY MESSAGES

- Heat index values between 100 and 105+ degrees are expected Tuesday through Thursday. There is a high chance (>60%) of heat index values exceeding 100 degrees south of a line from Beardstown to Terre Haute on Tuesday, expanding to areas south of Interstate 74 on Wednesday. - More seasonal conditions arrive by late weekend, lowering high temperatures into the mid-80s behind a slow moving cold front. The passing cold front brings a low (20%) chance of showers and thunderstorms Friday and Saturday.

DISCUSSION

Issued at 113 PM CDT Mon Aug 31 2026

Late Summer Heat Wave Upper-level ridging remains dominant across the Midwest this week, supported by a robust nearly 600 dam 500mb high centered over the mid-Mississippi and Tennessee Valleys through Wednesday. The ridge axis is progged to shift toward the Mid- Atlantic coast by late week. Under this subsidence, temperatures will remain well above seasonal normals through the remainder of the week with most precipitation bypassing the local area to the north, though periodic convective threats may clip central Illinois.

Surface analysis this afternoon shows ridging along the Appalachians with low pressure over the Canadian Prairies, maintaining a southwesterly gradient across central Illinois and pushing ambient temperatures into the low to mid-90s. Dew point forecasting remains challenging as moisture advection is tempered by deep mixing into a very dry column. Current dew points in the mid-60s to lower 70s are yielding heat indices near 100 degrees.

Similar conditions are expected Tuesday and Wednesday, with an additional uptick in temperatures as the 850mb thermal ridge peaks between 24-27C -- values exceeding the 90th percentile of climatology. Surface highs will reach the mid to upper 90s, driving peak heat indices into the 100-105+ range. LREF probabilities for heat indices >100 degrees are high (>60%), focused south of a Beardstown to Terre Haute line on Tuesday and expanding south of I-74 on Wednesday. In collaboration with neighboring offices, the Heat Advisory was expanded to the remainder of the Central Illinois counties Tuesday through Thursday.

Slow Pattern Change Late Week and Weekend A strong shortwave trough will dig across the Great Lakes Wednesday night and Thursday, followed by a more potent wave over the weekend. This will shunt the primary upper ridge axis back over the Great Plains, transitioning central Illinois into a northwest flow regime. At the surface, Canadian high pressure building across Quebec will drive a backdoor cold front through Illinois. This boundary will serve as the focus for slight chance PoPs (20%) Friday and Saturday. Temperatures will moderate from the 90s ahead of the front Thursday and Friday to the mid-80s in its wake for at least parts of the area Sunday. The current Heat Advisory may require extension for portions of the area depending on the eventual frontal speed and precipitation coverage.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 605 PM CDT Mon Aug 31 2026

South to southwest winds expected to continue through the period, but overall should be a bit lighter on Wednesday than they were today. VFR conditions will prevail, with any high cloud cover mainly limited to areas north of KBMI/KPIA.,

CLIMATE

Issued at 440 PM CDT Mon Aug 31 2026

Record high temperatures this week:

Location Tue 9/1 Wed 9/2 Thu 9/3 ======== ======== ======== ======== Bloomington 102/1894 101/2011 102/1913 Champaign 102/2011 101/2011 99/2011 Charleston 99/2011 103/1953 100/1925 Danville 101/1953 101/1953 99/1913 Decatur 102/1953 102/1953 102/1913 Jacksonville 103/1913 103/2011 101/2011 Lincoln 102/1953 101/1953 100/1913 Olney 105/1953 106/1953 105/1925 Paris 101/1953 102/1953 101/1913 Peoria 101/1913 100/1913 99/1913 Springfield 102/2011 101/2011 100/2011

ILX WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 7 PM CDT Thursday for ILZ027>029-036-037- 040>044-047>056-061>063-066>068-071>073. Heat Advisory from 1 PM Tuesday to 7 PM CDT Thursday for ILZ030-031-038-045-046-057.