textproduct: Central Illinois

KEY MESSAGES

- There is a Marginal Risk (level 1 of 5) for severe weather this afternoon and evening along and south of a Rushville...to Decatur...to Terre Haute line. The main risk will be isolated damaging wind gusts.

- The first prolonged heatwave of the summer will arrive next week when air temperatures rise into the 90s and maximum heat index values climb well above 100 degrees Monday through at least Thursday.

DISCUSSION

Issued at 405 AM CDT Sat Jun 27 2026

*** Marginal Severe Weather Risk ***

08z/3am surface analysis shows a stationary frontal boundary extending from southern Indiana westward to Kansas. Several clusters of convection are ongoing south of the boundary with the most significant storms focused across southern Kansas into Oklahoma. Meanwhile north of the front, scattered light showers are evident across central Illinois. The boundary will remain nearly stationary today, then will slowly shift northward tonight in response to rising upper heights. Extensive cloud cover will keep much of the KILX CWA relatively stable today: however, as temperatures climb into the upper 70s and lower 80s and dewpoints hover in the lower to middle 70s, modest destabilization will occur south of the I-72 corridor during peak heating with the 00z HREF showing mean SBCAPEs reaching 1000-1500J/kg. Wind shear will remain quite weak, with the NAM indicating 0-6km bulk shear of less than 30kt. Scattered thunderstorm cells will develop within the frontal zone, but parameters do not support organization or particularly vigorous updrafts. As a result, the risk for severe weather will remain low...with a few of the stronger storms perhaps producing gusty winds between 3pm and 10pm along/south of a Rushville...to Decatur...to Terre Haute line. Scattered showers and thunderstorms will develop across the remainder of central Illinois later tonight into Sunday morning as the front lifts northward: however, severe weather is not anticipated.

*** Hot Weather Ahead ***

After the recent stretch of below normal temperatures, a distinct pattern change will bring summertime heat back to central Illinois for the week ahead. As upper-level ridging builds over the Midwest, the persistent frontal boundary will get pushed well to the north and temperatures will rise markedly. Clouds and a few showers early in the day will tend to blunt the warming trend on Sunday: however, afternoon highs will still reach the upper 80s to around 90 degrees. Rising heights and increasing amounts of sunshine will bring hotter conditions for Monday through Thursday when highs climb into the lower to middle 90s. With dewpoints in the middle to perhaps upper 70s, corresponding heat index values will exceed 100 degrees each afternoon. Given the increasing confidence of an extended period of heat/humidity, heat headlines will need to be issued over the next forecast cycle or two. Current projections indicate solid Heat Advisory conditions (heat index of 105-110) Monday through Thursday before the ridge axis shifts eastward and additional cloud cover and convection chances bring a slight cooling by the end of the week.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1234 AM CDT Sat Jun 27 2026

A warm front will remain draped over central IL the next 24 hours. Light rain or drizzle will continue overnight, gradually ending by daybreak. IFR to occasionally LIFR ceilings will be in place to start the period with MVFR ceilings returning as early as mid to late morning. Confidence in timing of VFR conditions remains low, though ceilings look to improve sooner at southern airfields (KSPI- KDEC-KCMI). 5-10 kt winds will generally remain out of the east to northeast through Saturday night.

ILX WATCHES/WARNINGS/ADVISORIES

None.