textproduct: Central Illinois

KEY MESSAGES

- Another round of thunderstorms will impact central Illinois Saturday night. There is a Slight Risk (level 2 of 5) for severe weather along and southwest of a Peoria to Mattoon line...with the primary risk being damaging wind gusts.

DISCUSSION

Issued at 126 PM CDT Fri Jun 12 2026

High pressure will ensure a mild/dry night across central Illinois as overnight low temperatures drop into the upper 50s and lower 60s. Skies will initially be clear this evening: however, an increase in mid/high clouds will be noted late. A short-wave trough tracking out of the central Rockies will interact with a 40-45kt nocturnal 850mb jet to trigger clusters of convection across Kansas into central/southern Missouri after midnight. As this activity shifts eastward, it will be encountering a drier and more subsident airmass across Illinois and will therefore be decreasing in intensity and areal coverage. While some models suggest completely dry conditions, others such as the HRRR and 12km NAM indicate at least scattered showers/thunder reaching south-central Illinois Saturday morning. Have therefore opted to carry slight chance PoPs (20%) along/south of a Macomb to Mattoon line from morning through mid-afternoon.

A cold front currently upstream across the Northern Plains will settle southward...bringing a better chance for showers and thunderstorms by Saturday evening. While moisture return will initially be limited, the NAM is indicating a narrow band of 70+ dewpoints immediately along and ahead of the boundary across southern Iowa/northern Missouri. With MUCAPE in excess of 3000J/kg and 0-6km shear of 35-45kt, a broken line of convection will develop along the front to the N/NW of the KILX CWA by late afternoon. These storms will then drop southeastward into the area during the evening, accompanied by an attendant scattered damaging wind risk. MUCAPE values rapidly decrease after sunset, so the exact eastward/southward extent of the severe risk is uncertain. The updated Day 2 Convective Outlook from SPC has subsequently pulled the risk to the southwest, dropping locations along and east of a Peoria to Mattoon line back into the Marginal Risk (level 1 of 5) category. Based on current trends showing the greatest instability and strongest LLJ further southwest across the Ozarks, this seems reasonable. Am therefore expecting a broken line of thunderstorms with scattered damaging wind gusts to spill into the Illinois River Valley as far east as the I-55 corridor during the mid to late evening...followed by a weakening of the storms as they push into east-central and southeast Illinois overnight.

Once the cold front passes, high pressure will build in from the Northern Plains and a period of cool and dry weather is expected for Sunday and Monday with highs only in the lower to middle 70s. After that, the next chance for precipitation will begin to come into the picture perhaps as early as Tuesday: however, most indications suggest the primary chance for showers/thunder in the extended holding off until late Wednesday into Thursday.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

Issued at 650 PM CDT Fri Jun 12 2026

A couple of weather features could bring showers and thunderstorms late in the 00Z TAF period, starting with a disturbance moving out of MO vicinity Saturday morning and keeping low chances for scattered shra/tsra at KSPI/KDEC after 14Z. The next feature will be a broken line of tsra approaching from NW near 00Z Sunday. Have incorporated VCSH at KSPI/DEC after 14Z/15Z, and PROB30 for tsra at KPIA after 23Z. Cloud cover will be gradually increasing, but VFR conditions expected outside any tsra. Winds W-SW 5-10 kts this evening, becoming light and variable after around 03Z, then SSW 10-15 kts with a few higher gusts after 14Z.

ILX WATCHES/WARNINGS/ADVISORIES

None.