textproduct: Central Illinois

KEY MESSAGES

- A dangerous severe weather outbreak is projected for for central IL on Wednesday, featuring tornadoes, damaging straight line winds, and large hail.

- Heavy rainfall rates will create a risk of localized flash flooding on Wednesday, particularly for areas near and north of I-74.

- Strong, non-convective gradient winds are anticipated Wednesday afternoon, with widespread southwest gusts near 45 mph, particularly for areas near and south of I-72.

UPDATE

Issued at 905 PM CDT Tue Jun 16 2026

A corridor of MLCAPE values 500-100 J/KG and 50 kt bulk shear continues south of I-70, with isolated storms along a zone of convergence associated with a cold front. This supports a continued threat of isolated severe storms, and a Severe Thunderstorm Watch continues until 10 PM. Otherwise, the storm activity should move out of the area in the next few hours, with the next chances for storms to arrive in the Illinois River Valley after sunrise.

DISCUSSION

Issued at 235 PM CDT Tue Jun 16 2026

Isolated severe storms east of I-57 this afternoon...

A vigorous mid-level shortwave is currently pivoting into the east central WI, with a trailing cold front pushing east of the IL River at 18z. Ahead of the front dewpoints are climbing to around 60F over eastern IL, contributing the MLCAPEs around 500 J/kg. Steady cooling aloft south of the upper wave, combined with deep layer shear around 50 kt, should allow for isolated to scattered storm development east of I-57 this afternoon. Thermodynamic profiles support an environment favorable for low- topped supercells capable of hail greater than 1" diameter and isolated damaging wind gusts. This activity should push south near I-70 by early evening in a weakening mode as the upper support pulls farther northeast.

Moderate risk of severe weather Wednesday...

A strong mid-level shortwave will track into the Upper Mississippi Valley, associated with and unseasonably strong 990 mb surface low. Mass field response south of the low is impressive, with ECMWF EFI highlighting an event at the top of mid June climatology in several kinematic and moisture fields. A 50-60 kt 850 mb low- level jet will aggressively transport deep moisture into central and southeast Illinois overnight and into Wednesday morning. Precipitable water values are forecast to climb toward 2.0 inches, creating a high-efficiency environment for torrential rainfall. Strong low and deep layer shear will promote well organized and long lived storms capable of strong, long-track tornadoes, destructive straight line winds, and large hail.

The first round of convective activity is projected to move into the region from the west during the morning hours, roughly between 7 AM and 1 PM. CAMs suggest this activity will primarily affect areas north of the I-72 corridor. High rain rates accompanying this round, combined with antecedent soil moisture, create a distinct threat for localized flash flooding. Training storm cells are likely, particularly near and north of I-74, prompting the issuance of a Flash Flood Watch for these locations. In addition to the flash flood threat, the morning round of storms looks to mainly be elevated but supported by strong effective shear. Consequently, these storms will primarily carry a risk for large hail. If storms can become rooted to the surface, there is a non-zero risk for damaging winds and a few tornadoes. The morning activity is significant not only for its immediate hazards but also for its potential to deposit an outflow boundary/effective warm front across the region, which will play a crucial role in the evolution of the atmosphere ahead of the primary afternoon severe weather event.

The atmosphere is primed for a significant severe weather event Wed afternoon. Behind the morning convective activity, rapid destabilization is projected, with MLCAPE values likely surging into the 2500-3500 J/kg range and dewpoints reaching the lower 70s south of the boundary. This instability, combined with impressive bulk shear values (60-75 knots), creates a highly favorable environment for high-end severe storms. SPCs Day 2 Outlook highlights a Moderate Risk (Level 4/5) for our area, reflecting the high confidence in an outbreak of all severe hazards. Discrete supercells are projected to initiate mid-to- late afternoon along a strong cold front pushing into central IL. These storms will pose an immediate threat for large hail, potentially exceeding 2 inches in diameter, and the development of strong (EF3+), long-tracked tornadoes. Shear vectors oriented favorably off the boundary will likely promote discrete cells persisting for several hours. Given the strong mid-level flow, storm motion will be fast at 50-60 mph to the east, or southeast for right movers. Eventually, cold pool interactions will foster upscale growth of these supercells into a linear structure during the evening. This line will favor destructive, straight-line wind gusts for east central and SE IL, with line- embedded mesovortex tornadoes possible.

Looking at possible failure modes for widespread/intense severe...while parameters are lining up well, forecast soundings exhibit mid level winds at 70-90 kt. Local studies have noted in past events when mid level winds exceed 80 kt, updrafts have difficulty persisting and can get tilted/blown downstream before growing tall enough to produce significant severe weather. Will have to see if this has any impact on coverage or intensity of this event.

Aside from the storm related hazards, an out of season gradient wind event appears likely Wednesday afternoon driven by the deep surface low just to our north. High-res guidance shows southwesterly 45 mph wind gusts becoming likely, particularly near and south of I-72. A Wind Advisory has been issued for these areas from 1 PM to 7 PM. Crop canopy looks to be fairly closed at this point, though any fields that remain open/recently worked will carry a blowing dust risk.

Calmer, more stable conditions arrive Thursday and Friday as the system departs and high pressure builds across the region. Temperatures will remain seasonable, generally in the mid 70s to low 80s.

By Saturday night and into the start of next week, the upper- level pattern transitions into a zonal flow, reintroducing active weather. The GFS and ECMWF show some divergence regarding the specific timing of shortwave impulses, resulting in lower confidence for exact precipitation timing. However, an unsettled pattern is the most likely outcome, with the CPC 6-10 day outlook suggesting a trend toward below-normal temperatures and above-normal precipitation. AI/ML severe products show some low probabilities for severe working back into the Midwest on Sunday.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 558 PM CDT Tue Jun 16 2026

Cold front has slipped south of the central IL terminals. WNW winds gusting at 20-25 kt will quickly subside around 01z, with light/variable winds being common overnight. Southeast winds will pick up after sunrise, gusting near 25 kt into midday. As deep surface low pressure tracks to our north, winds veer southwest for the afternoon, and gust 30-40 kt in a tightening pressure gradient. Two rounds of scattered TSRA appear likely on Wed, one mid to late morning, and another mid to late afternoon. Variable/gusty winds and brief IFR conditions will accompany the storms if a terminal is impacted.

ILX WATCHES/WARNINGS/ADVISORIES

Flood Watch from 7 AM CDT Wednesday through Wednesday evening for ILZ027>031-036>038. Wind Advisory from 1 PM to 7 PM CDT Wednesday for ILZ040>057- 061>063-066>068-071>073.