textproduct: Central Illinois

KEY MESSAGES

- An upper system over Kansas will slowly lift into IL by Monday afternoon, bringing isolated to scattered showers and thunderstorms today through Monday night over central and southeast IL. There is a 30 to 70% chance for total rainfall to exceed 1 inch.

- Summertime heat and humidity will prevail through mid week over central and southeast IL, with afternoon heat indices peaking in the upper 90s and lower 100s Tuesday through Thursday.

DISCUSSION

Issued at 330 AM CDT Sun Jun 7 2026

A persistent cluster of showers and thunderstorms brought very heavy rains to the northeast half of Vermilion county Saturday evening, including the Danville area where up to 6.4 inches of rain fell in Bismarck and the Danville airport, with as much as 2-3 inches per hour at mid evening. Radar mosaic currently shows widely scattered showers ne of Vermilion county IL over northern IN, in nw IL between Peru and Quad Cities, sw of a Macomb to Litchfield to Marion line and near Lawrenceville, IL. Scattered convection was found over MO with cluster of thunderstorms in the KC area. The 08Z/3 am surface map shows a frontal boundary over northern IL/IN near I-80 and into northeast Iowa. Mild and muggy conditions continued over CWA with temps in the low to mid 70s and dewpoints in the upper 60s/lower 70s with light south to sw winds. High PW values were 1.6-1.9 inches over central and southern IL in warm sector from I-80 south.

Boundary to be close to northeast CWA today where best chances of convection to be today especially this afternoon, and also over west central IL with approaching upper level low/trof from south central KS that moves into IA/MO as it opens up tonight. SPC day1 outlook keeps marginal risk of severe storms this afternoon/evening over the Ozarks of central/southern MO into central/northern AR and southern/sw IL south of I-64 where more unstable airmass will be. WPC ERO does have marginal to slight risk of excessive rainfall over central IL this afternoon and tonight, with the higher chances over northern CWA closer to boundary. Very warm and humid again today with highs in the mid to upper 80s (near 90F in Lawrenceville). Muggy dewpoints in the upper 60s/lower 70s to give afternoon heat indices peaking in the lower 90s. Not as breezy as past few days with se winds 5-15 mph so not providing much relief. Lows overnight in the upper 60s and lower 70s.

Best chances of convection over central/se IL appears to be on Monday and Mon evening as upper level trof moves into IL Mon afternoon. More unstable airmass still to our sw with CAPES rising to 1500-2500 j/kg in sw IL near MO border by late Mon afternoon. SPC Day2 outlook has marginal risk over southern IL south of I-64 into southeast MO and western KY. But tropical PW values rising over 2 inches supports WPC ERO slight risk over IL Mon/Mon night. HREF LPMM shows pockets of 1-3 inches of pcpn in 6 hours with even a few isolated spots of 3-5 inches. Seeing what happened near Danville and into parts of west central IN yesterday aftn/evening, fell this is a good possibility with even higher PW values possible. More cloud cover and convection around on Mon with keeps seasonable highs in the low to mid 80s but humid with dewpoints in the lower 70s with afternoon heat indices around 90F with south breezes 10-15 mph and gusts 15-25 mph.

The weakening upper level trof shifts east of IL into IN/OH/KY on Tue though still close enough to have chance of showers/thunderstorms lingering Tue especially in eastern IL. Warmer on Tue with more sunshine by Tue afternoon, with upper 80s eastern IL and lower 90s in western CWA, west of highway 51. Dewpoints in the low to mid 70s with afternoon heat indices in the mid to upper 90s west of I-57 where more sunshine possible along with warmer temps. We have isolated chances of convection Tue night and near the Wabash river valley on Wed. Wed appears to be the warmest day with highs in the low to mid 90s and afternoon heat indices 98-104F, warmest over the IL river valley west into the MS river valley area. This would be just shy of heat advisory criteria of 105F and will need to be watched especially for our western CWA.

Forecast models showing more agreement with a cold front moving se over IL Thu afternoon/evening and likely bringing a round of thunderstorms. Still some timing differences with movement of cold front. SPC Day 5 outlook has slight 15% risk of severe storms over central IL (about a county southeast of I-70) on Thu/Thu night, mainly Thu afternoon/evening. Very warm and humid ahead of this front on Thu with highs in the lower 90s and heat indices in the upper 90s to near 100F. Convection chances to diminish from nw to se behind the cold front overnight Thu night into early Fri morning. Looks drier now on Friday with highs in the mid to upper 80s and dewpoints in the mid to upper 60s. Models differ with solutions this weekend with another wx system and cold front moving through by Sat night. NBM pops of 20% Saturday and Sunday (30% Sat night). Temps trending cooler toward seasonable levels by next Sunday along with less humid air.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 615 AM CDT Sun Jun 7 2026

Some lower clouds around 1500 feet have developed in a narrow clear slot from KGBG-KCMI early this morning, and a brief period of MVFR conditions cannot be ruled out in this corridor over the next hour or so. However, the main period of lower ceilings will be toward the end of the period, with HREF probabilities below 3000 feet ranging from 40-70%.

Timing and placement of developing showers/storms remains a challenge, though high-res models are most bullish on the period from 18-24z. A few are lingering the activity near KPIA/KBMI into early evening as well.

ILX WATCHES/WARNINGS/ADVISORIES

None.