textproduct: Central Illinois

KEY MESSAGES

- There is a Slight Risk (level 2 of 5) of severe weather along and southwest of a Peoria to Mattoon line tonight...with the primary hazard being scattered damaging wind gusts.

- After a brief lull, strong to potentially severe thunderstorms return to the forecast by Wednesday.

DISCUSSION

Issued at 242 PM CDT Sat Jun 13 2026

19z/2pm surface analysis shows a cold front extending from Wisconsin southwestward to near Kansas City...while a stationary frontal boundary remains draped across the Ozarks into the Tennessee River Valley. Widely scattered convection is currently ongoing along and just south of the I-72 corridor. Meanwhile further northwest, a few cells have developed along and behind the advancing cold front over western Iowa. While CAMs have generally not handled the present convection very well today, there has been a clear trend toward less storm coverage with FROPA tonight. Regional mesoanalysis shows a weakly unstable/sheared environment across central Illinois this afternoon with MLCAPEs of 500-1000J/kg and 0-6km bulk shear of less than 30kt. RAP analysis indicates MLCAPEs rising to 2000-2500J/kg ahead of the cold front across eastern Iowa/northwestern Illinois after 23z/6pm as surface dewpoints reach the lower 70s. Scattered thunderstorms will develop within this instability axis, then gradually settle southeastward into central Illinois later this evening into the overnight hours. As has been seen by the past few model runs, instability will rapidly decrease after sunset...with the greatest instability tied to a 40-45kt 850mb jet further southwest across Missouri. As such, think a broken line of thunderstorms will track into the Illinois River Valley after 02z/9pm accompanied by scattered damaging wind gusts. As the line advances southeastward, it will quickly lose steam and the severe weather risk will decrease overnight. The latest Day 1 Convective Outlook from SPC highlights locations south of the stationary front across eastern Kansas into Missouri where the low-level jet will provide continued instability well after dark. Further northeast in central Illinois, a Slight Risk (level 2 of 5) remains in place along/southwest of a Peoria to Mattoon line to account for the low-end damaging wind risk later this evening.

Thunderstorms will quickly decrease in intensity and areal coverage overnight, with overcast conditions and a few lingering showers remaining by Sunday morning. Once the front pushes further to the east, the showers will end and skies will become partly to mostly sunny across the board by afternoon. As high pressure builds into the region, a period of cool/dry weather will be on tap Sunday afternoon through Monday night...with highs only in the lower to middle 70s and lows dipping into the lower to middle 50s.

As the high departs, a weak cold front is slated to push into the region on Tuesday. The boundary will have limited deep-layer moisture available, but will have sufficient forcing to warrant high chance to likely PoPs (40-60% chance) by peak heating Tuesday afternoon. Things get more interesting after that as the boundary stalls across the Ohio River Valley Tuesday night, then begins to return northward as a warm front on Wednesday. There is still a good deal of model spread at that time range, so the exact details are still unknown. However, both the 12z Jun 13 GFS and ECMWF show low pressure tracking along the warm front, resulting in a round of strong to severe convection most likely Wednesday afternoon/evening. The GFS is a bit further south with the boundary, but both models indicate a highly unstable/sheared environment capable of producing thunderstorms with all severe hazards possible. As such, SPC has highlighted a large swath of the Midwest including all of central/southeast Illinois with a 15-30% chance for severe. Stay tuned to later forecasts for additional details.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 619 PM CDT Sat Jun 13 2026

A broken line of thunderstorms associated with a cold front approaching from the northwest is expected to arrive in the area around 04Z-05Z and progress across the central IL terminals through 08Z-09Z. A few of these storms could have strong wind gusts to 50 kts, although more typical gusts would be 30-40 kts. Scattered showers and MVFR cigs look to trail this line of thunderstorms from around 12Z-15Z, then clearing skies are expected. Surface winds S 5-10 kts this evening, shifting to NW behind the thunderstorms around 08Z-09Z, increasing to around 15 kts with gusts 20-25 kts by around 18Z.

ILX WATCHES/WARNINGS/ADVISORIES

None.