textproduct: Central Illinois

KEY MESSAGES

- A Flood Watch is posted today and evening for central and southeast IL. A few waves of showers and thunderstorms expected today and could produce locally heavy rain of 2 to 3 inches per hour rates.

- High heat and humidity will build across the region Tuesday through Thursday, driving afternoon heat index values into the upper 90s and lower 100s. More comfortable temperatures and humidity levels are expected by early next week.

- There is a Slight to Enhanced risk of severe storms from the IL river nw Wed night. There is a 15-30% risk of severe storms over central and southeast IL Thu and Thu evening as cold front moves through Thu night.

DISCUSSION

Issued at 400 AM CDT Mon Jun 8 2026

Issued a Flood Watch for central and southeast IL today and evening. Some bands of showers and thunderstorms to pivot north and ne across the areas today, with best chances of convection shifting into east central and southeast IL this evening. Unseasonably high precipitatable water values will be 2-2.25 inches at times today and evening over the CWA. Thunderstorms could produce locally heavy rains of 2-3 inches per hour rates and to be more widespread than the past few days as mid level trof moves into IL this afternoon. WPC Day1 ERO has slight risk of excessive rainfall across CWA today/evening with southeast IL (Terre Haute to Shelbyville south) having a 25% risk of rainfall exceeding flash flood guidance within 25 miles of a point.

A mid level trough over western MO/IA early this morning will move northeastward today across the mid Mississippi Valley. Deep tropical moisture continues streaming over IL ahead of approaching trof with PW of 2-2.25 inches into this evening. Weak steering flow aloft to also support heavy rain threat. Will Moderate instability is forecast into southern Illinois this afternoon along with enough wind shear to support marginal risk of severe storms from mid afternoon into early evening in southeast IL. Main severe storm threat is damaging wind gusts while also a 2% risk of tornadoes from highway 50 south. The RAP 13 Layer Nonsupercell tornado parameter has pockets of 1-3 over central IL from mid day into the afternoon. So we will need to be alert for possibility of a few brief funnels/tornadoes in tropical air mass. Highs today of 80-85F, warmest near Lawrenceville with muggy dewpoints in the low to mid 70s.

Convection chances to become more widely scattered from west to east during tonight as mid level trof shifts east into Indiana tonight and instability wanes. Moderate to heavy rains still possible over east central and especially southeast IL during early to mid evening. Lows overnight in the upper 60s to around 70F.

Mid level trof continues moving east over the Ohio river valley on Tue with upper level ridging into IL as 500 mb heights rise to 588-590 decameters by Tue afternoon over CWA. SPC Day2 has marginal risk of severe storms over CWA Tue afternoon/early Tue evening as an unstable air mass lingers over the area with very warm temperatures in upper 80s to around 90F and moist dewpoints in the low to mid 70s. Large hail and damaging wind gusts will exists with any storms that can become sustained in that thermodynamic environment from mid Tue afternoon into early Tue evening until sunset.

Mid/upper level ridge over IL on Wed and this to keep most of area dry much of the day Wed along with hot and humid conditions. Highs Wed in the lower 90s and dewpoints in the low to mid 70s to give afternoon heat indices in upper 90s and lower 100s (highest over the IL/MS river valleys). Will see breezier sw winds on Wed with gusts 20-30 mph especially Wed afternoon due to tightening pressure gradient.

Per SPC Day3 Outlook for Wed night, they have a slight risk of severe storms from the IL river nw and enhanced risk over nw parts of Knox and Stark counties. (Also have a Level 1 intensity of severe nw of the IL river). Here is SPC's discussion on this severe threat for Day 3 (Wed afternoon/Wed night)...A very moist boundary layer, characterized by boundary layer dewpoints in the upper 60s to mid 70s is forecast ahead of a cold front, which coupled with steep lapse rates, will contribute to moderate to strong instability Wed afternoon. Thunderstorms are expected to develop over IA and the lower MO Valley by mid to late Wed afternoon. The strongest deep layer shear is forecast across the upper MS Valley into upper Midwest, with decreasing bulk shear magnitudes with southward extent being offset by stronger instability. The CAPE/shear parameter space will favor organized storm modes including supercells and bowing structures. Large to very large hail will likely be the initial hazard, with the threat for damaging winds and tornadoes increasing as storms move into northwest IL, where stronger low level shear is forecast.

SPC Day4 Outlook has 15-30% risk of severe storms over CWA on Thu especially Thu aftn/evening. The highest risk is from Champaign to Litchfield northwest. We will likely be in a severe risk on Thursday (especially Thu afternoon/evening) as line of storms pushes se over central and southeast IL into a very unstable air mass with stronger wind shear present due to 50-70 kt mid level jet streak. Per SPC Day4 discussion...There is some model signal that a corridor of enhanced tornado potential could develop along and south of the surface low track from eastern IA and northern IL. That potential scenario will be dictated by the location of the effective surface boundary. High heat and humidity ahead of the storms especially se half of CWA where highs around 90F to lower 90s and afternoon heat indices peaking in the upper 90s to near 100F before the storms move in. Precipitatable water values remain high on Thu so heavy rains are a threat especially if training occurs. WPC Day5 ERO has marginal risk of excessive rainfall across IL on Thu/Thu night.

Quieter weather expected on Friday behind the cold front with just slight chance of convection southeast of I-70 Fri morning, with better chances of convection shifting se of CWA. The ECMWF, GEM and GFS models keep much of area dry Fri through Saturday though NBM and WPC have 20-40% pops Fri night and Saturday. Still fairly warm Fri/Sat with highs in the mid to upper 80s and a bit sticky with dewpoints in the 60s both days. Another cold front to push into central/se IL around Sunday and to bring a chance of showers and thunderstorms Sat night and Sunday, followed by cooler and less humid air early next week (highs upper 70s/lower 80s Sun/Mon June 14-15).

The Climate Prediction Center (CPC) 8-14 Day outlook for June 15-21st has a 35-45% chance of below normal temperatures over IL with 35-40% chance of above normal precipitation.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 1227 AM CDT Mon Jun 8 2026

While conditions start off VFR, evening ensemble guidance is in good agreement with a period of MVFR ceilings starting as early as 12z near KSPI/KDEC, and encompassing all of central Illinois much of the morning. A general rising in ceilings should take place around midday, mostly in the 3-4kft range. However, as low pressure passes by eastern Illinois this evening, chances of ceilings dropping back below 3000 feet from KDEC-KBMI east are around 40%.

Thunderstorm trends are a little more uncertain. In the short term, bulk of the thunder activity should be in western Illinois, with scattered showers and a few storms in central Illinois 12-18z. The afternoon hours should continue to see an overall increase in convection as daytime heating takes hold, and highest chances (TEMPO mentions vs. PROB30) are focused during this time period.

ILX WATCHES/WARNINGS/ADVISORIES

Flood Watch from 7 AM CDT this morning through late tonight for ILZ027>031-036>038-040>057-061>063-066>068-071>073.