textproduct: Central Illinois

KEY MESSAGES

- A weakening line of storms will move through central Illinois this morning, bringing a low (less than 15% chance) risk of damaging winds or hail.

- Additional storms may develop near Interstate 70 around midday, threatening the area with damaging winds, large hail, and torrential rainfall.

- Saturated ground from recent heavy rains creates a lingering flash flood risk near Interstate 70, though the chance of exceeding flooding rainfall rates is low (20% or less).

DISCUSSION

Issued at 318 AM CDT Tue May 19 2026

Remnants of a linear MCS persist over west-central Illinois early this morning. While the activity has generally remained sub-severe, the mesoscale environment remains capable of producing occasional damaging wind gusts. Sustenance of the current ragged convective line is being supported by approximately 30-35 kts of effective layer shear, driven by a 50-60 kt low-level jet (LLJ) core veering in ahead of the system.

Thermodynamic profiles ahead of the line are characterized by modest MUCAPE near 1500 J/kg, supported by favorable mid-level lapse rates exceeding 7 C/km, suggesting that isolated large hail cannot be entirely discounted. The potential for localized downbursts remains a focus as DCAPE values over 1000 J/kg combined with localized evaporative cooling and mid-level dry air could occasionally breach the morning inversion. Conversely, the tornado risk is considered minimal due to marginal low- level shear and an unfavorable storm-relative vector orientation. Nevertheless, convection should continue through the late morning as it nears the I-55 corridor, though it is expected to weaken as the primary mid-level shortwave moves north of I-80 and the LLJ recedes.

Regarding precipitation, rainfall rates have remained modest. MRMS data indicates one-hour rates generally at or below one inch, a trend supported by high-resolution guidance as the line continues its gradual decay through the morning hours.

Convective redevelopment is expected to remain suppressed north of Interstate 72 for the rest of the day, consistent with the stabilization caused by this mornings convective debris. The area near and south of I-70 presents the main concern for later today due to a higher potential for destabilization. Morning convective outflows are not expected to reach this southern region until approximately Noon (17z). HREF data indicates about 2000 J/kg of SBCAPE in this vicinity, which, when combined with a subtle mid-level shortwave, could increase effective-layer shear to near 30 kts. These conditions may briefly reinvigorate convective outflows, potentially resulting in damaging winds, large hail, and torrential rainfall.

A heavy rainfall potential is particularly concerning given the wet antecedent conditions, with recent observations of 3-4 inches of rain across portions of Effingham, Clay, and Jasper counties. Flash flood guidance indicates that rainfall exceeding 1.25 inches per hour today could trigger widespread flooding. While current HREF guidance suggests a low probability (20% or less) of reaching these rates, the risk remains a focal point due to the saturated ground.

Scattered showers may linger across southeast Illinois through Wednesday morning, with increased baroclinicity/frontogenesis behind the departed cold front. Rainfall amounts would be light should this occur, and the chances will be fleeting as a drier, cooler continental air mass settles over the Midwest.

Precipitation is expected to return by Friday following a brief period of seasonably cool conditions. As surface high pressure shifts to the east, a robust mid-level shortwave is forecast to track into the central United States. This pattern, characterized by a steady stream of Gulf moisture and a series of minor impulses originating from the Southern Plains, will keep central Illinois susceptible to multiple rounds of scattered showers. While weak kinematic profiles should largely mitigate the risk of severe weather, a gradual increase in instability over the weekend may support the development of scattered thunderstorms.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 554 AM CDT Tue May 19 2026

Scattered showers persist this morning with transient MVFR/IFR cigs. A tempo group has been added to account for this activity amid an otherwise VFR pattern. Winds will veer from southwest to north throughout this TAF period as a cold front pushes through the central Illinois terminals. Thinking most thunderstorm activity will stay south of the terminals through this evening, so any prob30 groups mentioned this afternoon ahead of the front currently exclude tsra mention.

Clouds will lift and break late tonight as a drier, cooler airmass settles over the Midwest.

ILX WATCHES/WARNINGS/ADVISORIES

None.