textproduct: Central Illinois

KEY MESSAGES

- Widespread heat continues through Thursday, though increasing cloud cover keeps the chance of heat index values exceeding 100 degrees at around 20 percent south of Interstate 72.

- Two rounds of severe thunderstorms will move across central Illinois this afternoon through tonight, bringing a primary hazard of damaging winds alongside localized tornado, large hail, and flooding threats.

- A cold front brings another round of severe storms Thursday evening and overnight, where damaging straight-line winds remain the main concern.

UPDATE

Issued at 359 PM CDT Wed Jun 10 2026

*** 21z Mesoscale Update ***

Strong to severe storms continue near the I-55 corridor as of this writing. RAP-based mesoA suggest storms are moving into an environment of gradually decreasing shear (25 kts or less along and east of the I-57 corridor). However, the thermodynamic profile remains supportive of sproadic severe gusts, with DCAPE values over 1000 J/kg all the way east to the IL/IN border. The expectation is storms persist, occasionally producing severe gusts, but the frequency/coverage of severe gusts should gradually diminish into the late afternoon.

Further west, satellite imagery shows outflow boundary from our ongoing convective complex draped from Macoupin Co (IL) to Randolph Co (MO), with additional storms firing along and south of this boundary. The suspected next wave of severe storms has fired across S IA/N MO, however, in the wake of the expansive cirrus shield associated with our ongoing storms, there is a lack of a cumulus field over NE MO/SE IA. There may not be sufficient recovery time for a robust, sfc-based severe threat with these storms as they progress east, and this suspicion is supported by WoFS which shows storms persisting eastward but becoming elevated. The severe threat into our area this evening is questionable. WoFS is starting to exhibit increasing confidence for a hydro threat, with a strong, multi-member signal for 2"+ rainfall totals as these S IA/N MO storms approach the ILX CWA closer to 00-01z (7-8 PM).

DISCUSSION

Issued at 1246 PM CDT Wed Jun 10 2026

Short Term Forecast: Heat and Severe Potential

Today and tomorrow will feature widespread temperatures in the 90s, with heat indices climbing into the upper 90s to lower 100s. Confidence in meeting Heat Advisory criteria (max heat index near 105F) remains low; LREF probabilities for heat indices exceeding 100F generally hold around 20 percent for areas south of I-72. Primary limiting factors for higher heat readings will be increasing cloud cover and precip chances along with convective debris, particularly on Thursday for the latter.

Thunderstorms are ongoing early this afternoon across portions of eastern Iowa and northeastern Missouri, with additional development expected to our west later this evening. Out ahead of the initial convective line, temperatures pushing 90 degrees and dew points in the low to mid-70s are supporting roughly 1500-2000 J/kg of weakly capped MLCAPE across central Illinois. Instability will further increase through mid-afternoon, peaking near 2500 J/kg. Effective bulk shear values will increase to around 30kt with the arrival of storms, sufficient to support an organized severe threat.

This initial line of storms is expected to lift northeast, likely staying near or just north of the I-72 corridor. While low-level flow is currently veered with unimpressive SRH values, this is forecast to increase ahead of the second line of storms. DCAPE values around 900-1200 J/kg, coupled with increasingly steep low-level lapse rates, will support a wind threat with the first wave of convection. Round two will see strengthened kinematic fields as storms congeal into a line and spread ESE across central Illinois late this evening. Damaging winds will remain the primary threat, though interactions with remnant outflow boundaries and increasing low-level winds associated with a strengthening low-level jet will support a localized tornado threat this evening. This threat will slowly subside with waning diurnal instability as the system moves east overnight.

In addition to the severe potential, multiple rounds of storms-- including the possibility for backbuilding and training--pose a localized flooding threat. Corfidi vectors ahead of the second line of storms drop below 10 kt and become oriented out of the northeast, suggesting potential for backbuilding along the southern periphery of the QLCS. While the severe threat should diminish overnight, the hydro threat may linger well into or through the overnight hours.

Thursday and Extended Period A robust shortwave trough is expected to lift into the Upper Midwest on Thursday, driving a cold front through central Illinois 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 remains seasonably strong Thursday. 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 exit quickly, 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, resulting in a much more comfortable air mass.

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 THURSDAY/

Issued at 1141 AM CDT Wed Jun 10 2026

Two rounds of thunderstorms, potentially severe, are expected to impact central Illinois through the period. The first is ongoing across eastern IA and northeast MO this hour and will move east across portions of central IL mainly north of the I-72 corridor this afternoon. The second line of storms will move across the region late this evening. Outside of the influence of storms, expect a moderate SSW breeze to prevail with gusts to around 20-25 kt during much of the daytime hours.

ILX WATCHES/WARNINGS/ADVISORIES

Flood Watch through Thursday morning for ILZ027>031-036>038- 040>043-047>051.