Area Forecast Discussion

KEY MESSAGES

- Another very warm and humid day expected over central and southeast IL, with heat indices peaking from 95-105 this afternoon.

- Thunderstorms will diminish east of the IL river early this morning. Another round of thunderstorms will spread southeast across the area late this afternoon and evening, and diminish late evening and overnight. There is a slight to enhanced risk of severe storms for damaging wind gusts, large hail, isolated tornadoes and localized flash flooding.

- More showers and thunderstorms are likely Saturday night with a marginal risk of severe storms and excessive rainfall over central IL.

DISCUSSION

Issued at 345 AM CDT Thu Jun 11 2026

Showers and thunderstorms were se of the IL river to along I-70 and tracking eastward. The severe threat has waned as outflow was pushing se of storm complex and instability weaker. But still getting reports of moderate to heavy rains with thunderstorms, with the heaviest rains were pushing se of a Champaign to Shelbyville line. We are getting recent reports of some flooding on west side of Decatur. The Flood Watch from Sangamon to Logan to DeWitt to McLean counties until 7 am will likely be able to cancel early especially nw counties. This MCS was supported by sw low level jet up to 35-40 kts earlier but is starting to weaken. Latest CAMs show convection pushing into southeast IL next few hours and diminishing by mid morning. Upstream a new MCS with convection was developing over south central and se Nebraska. Should then be a lull in convection part of today with areas nw of the IL river having chance of convection by mid or late afternoon. Breezy SW winds 15-25 mph and gusts 25-35 mph this afternoon (strongest nw CWA) to bring very warm conditions again today. Highs in the lower 90s from I-72 south where heat indices peak in the lower 100s this afternoon. Highs 85-90F north of I-72, with afternoon heat indices in the mid to upper 90s. HREF has a 50-80% chance of heat indices over 100F this afternoon along and sw of a Springfield to Terre Haute line.

Another band of strong to severe convection to move se over the IL river valley by late afternoon and over rest of CWA during this evening, and diminish late evening and overnight. SPC Day1 outlook has enhanced risk of severe storms from Danville to Litchfield nw and slight risk se of there. Damaging winds is biggest severe threat with 30-45% risk of damaging winds in enhanced risk area and also in Level 1 for winds potentially over 75 mph. Areas nw of I-55 are in level 1 for hail larger than 2 inch diameter. There is a level 1 for EF2 tornadoes north of I-72 with 10% or greater risk of tornadoes over the IL river valley. Very unstable air mass by afternoon with MLCAPES 3-4k j/kg while 0-6 km Bulk shear values 25-45 kts by late afternoon, highest nw of I-55. The lowest 1 km wind shear values are 15-25 kts, so the kinematic environment remains strong today. WPC also has marginal to slight chance of excessive rainfall this afternoon and evening, with the slight risk from I-72 north and 25% chance of exceeding Flash Flood Guidance over Knox, Stark and Marshall counties.

After cold frontal passage during this evening and early overnight, expect convection chances to diminish behind the front with decreasing clouds during overnight from nw to se and a fair amount of sunshine Friday as weak high pressure settles into the mid MS and lower Ohio river valleys. Expect cooler and much less humid air arriving on WNW winds. Seasonable highs Friday in the lower 80s with dewpoints mixing down into the upper 50s/lower 60s. Cooler lows Fri night in the lower 60s with fair weather.

A short wave trof to pivot east/se through the area by Saturday night with associated surface cold front pushing se over IL. SW breezes Saturday warms temps into the mid 80s while dewpoints rise back into the 60s. Will see more unstable air mass moving up from MO into central/sw IL, with the most unstable air over MO and southern IA where SPC has slight risk of severe storms late Sat afternoon and Sat evening. Deep layer wind shear also present. There is a marginal risk of severe storms over central IL Sat night. WPC ERO has marginal risk of excessive rainfall over central IL Sat night. A chance of showers/thunderstorms may linger in southeast IL Sunday morning, otherwise dry, cooler and less humid air returns on Sunday. Highs Sunday in the mid 70s in central IL and 75-80F in southeast IL.

Extended forecast models and their ensembles continues to show a broad mid/upper level trof over the Midwest, Great Lakes and Ohio river valley from Sunday through the middle of next week. There are northern stream short waves that pass through this trof at times and could bring chances of showers and isolated thunderstorms to central IL around Tue and again Wed afternoon into Thu. Highs Monday in the mid to upper 70s are upper 70s/lower 80s Tue/Wed.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 612 AM CDT Thu Jun 11 2026

An area of IFR ceilings has developed where skies cleared out earlier, with the moist ground from recent heavy rain. Main impacts have been west of a KPIA-KIJX line, but have started to show some breakup with sunrise. Think this should be gone before 14z.

Southwest winds will increase today and gust from 20-30 knots by about midday, lingering until passage of a cold front this evening. This front will bring a line of severe convection with it, with a short period of IFR visibilities in the heavier rain. The main period of concern for the terminals is from 23-03z. Once the front passes, winds shift to the west, and gradually diminish after midnight.

ILX WATCHES / WARNINGS / ADVISORIES

None.