Area Forecast Discussion

KEY MESSAGES

- Windy and much warmer conditions are on tap for Tuesday. There is a 40-80% chance of southwesterly wind gusts exceeding 30mph, which will push afternoon high temperatures into the middle to upper 70s.

- A storm system will spread widespread showers and thunderstorms into central Illinois Thursday night into Friday. At this time, it appears the risk for severe weather will remain low (less than a 15% chance).

DISCUSSION

Issued at 241 PM CDT Mon Apr 20 2026

*** Windy and Warmer on Tuesday ***

A sprawling ridge of high pressure extending from Hudson Bay to the Gulf Coast will shift eastward over the next 24 hours, allowing a warm/southerly return flow to develop across the Midwest. Models continue to show a 40-50kt low-level jet developing within the WAA regime from central/northern Missouri into the Southern Great Lakes tonight into Tuesday morning. As diurnal mixing commences, some of this higher momentum air will be drawn down to the surface by around 14z/9am as per the latest HRRR/RAP. The 12z HREF shows a 40-80% chance of gusts over 30mph along/north of a Litchfield to Danville line...with a 20-30% chance of gusts over 35mph for a couple hours prior to midday. The strong southwesterly winds in conjunction with partly to mostly sunny skies will help push afternoon highs well into the 70s.

*** Showers and a Few Thunderstorms Tuesday Night ***

A weak cold front is progged to drop southward into the region Tuesday night. The southward momentum of the boundary will be greatest across Ohio/Indiana, with the trailing front only slowly sinking southward further west across Illinois. As a result of the strongest frontal forcing, most models suggest the greatest areal coverage of convection will be further E/NE across central/northern Indiana. Given current set-up, have carried 30 PoPs along/west of the Illinois River...increasing to 50 PoPs along/northeast of a Bloomington to Champaign line. Moisture-pooling ahead of the front will be limited, with surface dewpoints only reaching the middle to upper 50s and resulting SBCAPEs generally less than 1500J/kg. While this is sufficient fuel for thunder, weak 0-6km bulk shear of 30kt or less will prevent organized storm development.

*** Higher Risk for Thunderstorms Thursday Night into Friday ***

After a period of warm/dry weather Wednesday and Thursday, the next significant storm system will push into the region by the end of the week. While minor timing discrepancies exist, both the 12z GFS and ECMWF suggest the associated cold front will swing through central Illinois around midday Friday. Favorable instability/shear parameters will be in place ahead of the system across the Plains late Thursday, resulting in a 15-30% chance for severe weather along/west of a Des Moines, Iowa to Tulsa, Oklahoma line. Some of this activity will spill eastward into central Illinois in a weakening state Thursday night into Friday morning. Diurnal de-stabilization will be greatest from the Ozarks southward into the lower Mississippi River Valley by Friday afternoon/evening. So while the local severe weather risk is non-zero on Friday, the highest probabilities (15-30% chance) will be focused from southern Missouri southward to Louisiana/east Texas.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 612 PM CDT Mon Apr 20 2026

A low level jet is expected to ramp up west of the Mississippi River this evening, shifting into central Illinois in the 06-08z time frame. However, conditions would be more borderline across eastern Illinois. Once the jet begins to mix to the surface Tuesday morning, expect south/southwest winds to gust from 25-30 knots through the afternoon. As a weak cold front drops south into the area, scattered showers and thunderstorms are expected to develop toward the end of the period. Right now, will only include a PROB30 at KPIA, with storm arrival at KBMI looking to be after 00z.

ILX WATCHES / WARNINGS / ADVISORIES

None.