textproduct: Central Illinois

KEY MESSAGES

- Scattered Severe Storms This Evening: Scattered thunderstorms will move through central Illinois this evening. The primary threat is localized damaging wind gusts from collapsing storms, along with downpours capable of producing 1 to 2 inches of rainfall.

- Wildfire Smoke Sunday: Smoke from Canadian wildfires will filter southwest across the area overnight, creating hazy skies through the day Sunday. Those sensitive to pollution should take precautions.

- Severe Weather Risk Late Monday: There is growing confidence in a more organized severe weather threat late Monday and Monday night. Severe storms capable of damaging winds and locally heavy rain are expected to sweep southeast into the region.

- Dry and Cooler Late Week: A strong high-pressure system brings a return to quiet weather from Wednesday through Friday. Expect dry conditions with comfortable, slightly below-normal temperatures in the low to mid-80s.

UPDATE

Issued at 723 PM CDT Sat Jul 18 2026

Cold front has roughly reached a Macomb-Hoopeston line early this evening. Radar currently shows a line of convection continuing to organize from just north of Quincy to Decatur, with another cluster of storms near Champaign and Danville. Severe activity thus far has been minimal, however downdraft CAPE's around 1000 J/kg (per our evening balloon sounding) along the line continue to point to localized strong wind gusts. Heavy rains are occurring with the stronger storms as well, as precipitable waters are in the 2 inch vicinity this hour. With weak shear, the storms overall should see a diminishing trend as we get closer to sunset. Most of the forecast area should be dry by midnight, though areas south of I-70 may see storms linger for another hour or two beyond that.

Regarding the incoming smoke, 21z/4pm runs of the HRRR and RRFS continue to support the earlier thinking of smoke beginning to spread into areas north of I-74 as early as 3 am, reaching a Macomb-Effingham line by around 7 am. RRFS visibility plots suggest 3-5 mile visibilities are plausible on Sunday. Air Quality Alert was issued earlier per Illinois EPA guidance.

DISCUSSION

Issued at 138 PM CDT Sat Jul 18 2026

Short Term Forecast & Convection Today... A west-east oriented frontal boundary currently resides near the I-80 corridor in northern Illinois and is making a slow southward progression into central Illinois. Ahead of this front, a warm and humid air mass remains in place with temperatures in the upper 80s to low 90s and dew points in the low to mid 70s. RAP guidance indicates MLCAPE values will peak in the 2500-3000 J/kg range this afternoon, though deep-layer shear remains modest at 20-25 kt. Given the lack of robust forcing and sub-optimal shear profiles, expect convective coverage to remain scattered, with some storm clustering likely. The primary hazard with this activity will be damaging wind gusts from collapsing cores. Additionally, with modest storm motions of 20-25 mph to the southeast, locally heavy rainfall is possible. HREF LPMM guidance highlights localized swaths of 1-2 inches of rain, which the ground should be able to handle given current 3-hour flash flood guidance generally running between 2 and 3 inches. Activity should wane after sunset, though lingering storms may persist into the overnight hours across portions of east-central and southeast Illinois.

Sunday Air Quality... Canadian and Upper Midwest wildfire activity continues to produce a significant smoke plume across portions of the Great Lakes and Upper Midwest this afternoon. Near-surface smoke guidance from the HRRR suggests this plume will filter southwest across central Illinois behind the cold front overnight tonight, lingering through the day Sunday. This smoke, combined with a post-frontal airmass, will likely inhibit insolation Sunday, resulting in temperatures slightly below normal, with highs topping out in the mid-80s. Slow improvement is expected through the day Monday as the front lifts back north across the region with south/southwest winds overspreading the area helping to clear out the smoke.

Monday Severe Weather Potential... The front is expected to lift back north across the region on Monday, allowing south-to-southwest flow to re-establish, pushing temperatures back into the upper 80s to lower 90s. With dew points surging into the mid-to-upper 70s, strong instability will develop, with MLCAPE values peaking around 3000 J/kg Monday afternoon and evening. As a shortwave trough digs across the Upper Midwest, deep-layer shear is forecast to increase significantly to 40-50 kt, creating a favorable parameter space for organized severe thunderstorms. Storms should initiate over the upper Midwest Monday afternoon, with a strengthening low- level jet supporting maintenance and propagation southeast along the instability gradient into central Illinois by late evening and overnight. This period warrants close monitoring for severe weather potential.

Extended Period... By Tuesday, storms are expected to clear the area along a trailing cold front. The remainder of the work week, from Wednesday onward, will feature dry conditions and slightly below-normal temperatures as a strong Canadian High settles across the Midwest. Highs are expected to remain in the low to mid-80s with no notable precipitation chances through the latter half of the week.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 610 PM CDT Sat Jul 18 2026

Main concern for thunder activity will be through about 03-04z, as a cold front pushes south. Based on the boundary position at 23z, KPIA threat for any more thunder is low, and KBMI will see the threat wane by 00z. MVFR or brief IFR visibilities are possible with the stronger storms.

As the cold front pushes further south, widespread smoke is expected to spread into central Illinois by daybreak, and persist through the day. Based on upstream observations across Wisconsin, will include a scattered 3500 foot layer of smoke. Visibility is a little harder to gauge as the smoke may dilute somewhat from the current upstream values, but will go with 5SM at all sites for now.

ILX WATCHES/WARNINGS/ADVISORIES

Air Quality Alert from midnight tonight to midnight CDT Sunday night for ILZ027>031-036>038-040>057-061>063-066>068-071>073.