textproduct: Central Illinois

KEY MESSAGES

- Slow moving thunderstorms will bring a localized risk of 2-3 inches of heavy rain to portions of central Illinois this afternoon through tonight. A few stronger storms could also produce isolated damaging wind gusts.

- Severe thunderstorms will impact the region Wednesday afternoon through Thursday night. Damaging straight-line winds are the primary hazard, but there remains a lesser threat of hail and an isolated tornado.

- High temperatures in the 90s will drive heat index values into the upper 90s and lower 100s Wednesday and Thursday. There is a 20 to 30 percent chance for heat index values in excess of 100.

DISCUSSION

Issued at 110 PM CDT Tue Jun 9 2026

Near-Term Outlook: Unsettled Pattern... The forecast area is locked into an unsettled weather pattern, featuring nearly daily opportunities for shower and thunderstorm development through the upcoming weekend. This afternoon, a remnant Mesoscale Convective Vortex (MCV) is tracking eastward near the I-72 corridor. Convection is currently intensifying within the warm advection wing just north of the MCVs track. SPC mesoanalysis reveals uncapped MLCAPE values of 1500-2500 J/kg ahead of this feature; however, effective shear remains modest at 20-25 kt. While weak shear may limit organized storm longevity, localized gusty winds and slow-moving or training convective elements present a threat for rainfall swaths of 2-3 inches. Farther south, near and south of I-70, a remnant outflow boundary is initiating isolated activity within an axis of higher instability, posing a limited severe threat primarily driven by damaging wind potential.

As we move into tonight, southwest flow aloft will reestablish across the region, supported by a strengthening low-level jet in the mid-Missouri Valley. While the most robust instability remains focused to our west, the gradient extends into portions of central Illinois, driving a warm air advection-driven chance for showers and storms that should shift northeast of the forecast area by daybreak Wednesday.

Mid-Week Heat and Severe Potential... Wednesday and Thursday will feature widespread temperatures in the 90s, with heat indices climbing into the upper 90s to lower 100s. At this time, confidence in meeting Heat Advisory criteria (max heat index near 105F) remains low, with LREF probabilities for heat indices exceeding 100F generally holding in the 20-30 percent range for areas south of I-70 on Wednesday and south of a Rushville to Terre Haute line on Thursday. The primary limiting factors for higher heat readings will be clouds and lingering convective debris.

By Wednesday afternoon, central Illinois will reside firmly within the warm sector as a warm front surges northward into Wisconsin, accompanied by breezy south to southwest winds. While modest capping and displacement from the primary forcing should maintain a largely dry first half of the day, we are monitoring two waves of potential thunderstorm development originating in Iowa and Missouri. These complexes may grow upscale and traverse portions of central Illinois from mid-afternoon through late evening. With MLCAPE values projected to exceed 2000 J/kg, deep- layer shear will be sufficient to support severe storms. Linear storm modes suggest wind will be the primary hazard, though the environment remains supportive of hail and the potential for an isolated tornado.

Late-Week Transition and Weekend Outlook... A robust shortwave trough is expected to lift into the Upper Midwest on Thursday, finally driving a cold front through central Illinois by Thursday evening and overnight. Ahead of this boundary, the GFS suggests a broad, unstable warm sector with MLCAPE values exceeding 3000 J/kg. Coupled with deep-layer shear of 25-35 kt and 0-1km shear of 15-25 kt, the kinematic environment is seasonably strong. While pre-frontal discrete activity with all severe hazards is possible, the primary concern remains straight-line winds as convective elements congeal into a line along and ahead of the front.

Lingering showers and storms over southeast Illinois on Friday morning will quickly exit, giving way to clearing skies as high pressure builds into the region. This will provide a brief return to more seasonal conditions, with highs in the lower to mid-80s and dew points mixing down into the upper 50s.

For the weekend and into early next week, the pattern turns more zonal aloft while a low-level baroclinic zone wobbles over the region. This setup maintains additional chances for showers and thunderstorms, though specifics regarding timing and coverage remain uncertain at this forecast range.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1221 PM CDT Tue Jun 9 2026

MVFR ceilings have developed late this morning and early afternoon, but anticipate these clouds will lift to VFR around the time the 18Z TAFs go into effect. Late this evening and overnight, a warm front lifting across the region will be the focus for scattered thunderstorms. Anticipated lower coverage and low confidence in the exact location of storm initiation precludes more than a prob30 mention at this time. SSW winds will prevail through the period outside the influence of any storms. Gusts to around 20 kt will develop by late morning Wednesday.

ILX WATCHES/WARNINGS/ADVISORIES

None.