textproduct: Central Illinois

KEY MESSAGES

- Widespread rain will occur across central Illinois on Sunday. The latest NBM indicates an 80-90% chance of greater than 1 inch...with a 40-50% chance of more than 3 inches in the Illinois River Valley.

- There is a Slight Risk (level 2 of 5) for severe weather along and south of a Jacksonville to Charleston line on Sunday.

DISCUSSION

Issued at 158 PM CDT Fri Jun 19 2026

*** Heavy Rainfall on Sunday ***

A vigorous short-wave trough evident on 18z/1pm water vapor over western British Columbia will dig southeastward into the Northern Rockies...helping eject a separate wave spinning off the coast of northern California eastward over the next 24-48 hours. As the California wave crosses the Rockies into the Plains, a large cluster of convection will form across Nebraska/Kansas Saturday afternoon/evening...then will push eastward into central Illinois late Saturday night into Sunday. With a 40-50kt 850mb jet streak oriented from Oklahoma northeastward into central Illinois ahead of the approaching wave, copious atmospheric moisture will be advected into the region as precipitable water values increase to 2.00-2.50. Given strong forcing and a steady supply of moisture, widespread rainfall is expected across all of central and southeast Illinois. As has been previously noted, the exact placement of the heaviest rainfall axis is still somewhat in question: however, the 12z Jun 19 synoptic models have all generally nudged it slightly southward from previous runs. WPC has shifted the heaviest band from a Peoria to Pontiac line southward to along the I-72 corridor accordingly. Meanwhile the 12z NBM shows a high probability (80-90% chance) of greater than 1 inch across the board...with a 40-50% chance of more than 3 inches focused in the Illinois River Valley. If current trends persist, think the NBM will shift its highest probabilities a bit southward as well. As it stands now, think a broad swath of 1.50 to 2.50 will occur...with a band of potentially higher amounts along/near the I-72 corridor. Since the soil is saturated and water is still standing in several area fields, rainfall of this magnitude will lead to steep rises on creeks and streams and create pockets of flash flooding. As a result, a Flood Watch will be carefully considered with upcoming forecast updates.

*** Severe Weather Potential on Sunday ***

The Storm Prediction Center (SPC) has added a Slight Risk (level 2 of 5) for severe along/south of a Jacksonville to Charleston line for Sunday. Model solutions still exhibit a good deal of variability: however, the overall trend has been to shift the track of the surface low further south either across the heart of central Illinois or along the I-70 corridor. The 12z NAM is a notable outlier, featuring a further north track and a much deeper low. If this particular scenario pans out, central Illinois could be in store for another round of significant severe weather. Will continue to monitor future runs, but for now will side with the GFS/ECMWF consensus. An MCS will track across central Illinois Sunday morning through mid-afternoon, resulting in heavy rainfall and potential flooding concerns. This system will leave behind an outflow boundary that will serve as the focus for strong to severe convection during the late afternoon and evening. Given the southward low track trend, it appears the most likely location for the boundary and the subsequent severe risk will focus across central/southern Missouri into the Ohio River Valley. This could still potentially impact the southern KILX CWA within the Slight Risk area, but the most likely scenario would be further south across the Ozarks into far southern Illinois and western Kentucky where a strongly unstable (SBCAPEs 2500-3500J/kg) and moderately sheared (0-6km shear 30-40kt) environment will exist. Stay tuned to later forecasts for additional details.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 1214 PM CDT Fri Jun 19 2026

A modest WNW breeze of 7-10 kt and VFR conditions will continue the remainder of today. This evening and overnight, winds will go light and variable while widely scattered light showers or sprinkles overspread portions of central Illinois. Light northwest winds set up again mid to late Saturday morning.

ILX WATCHES/WARNINGS/ADVISORIES

None.