textproduct: Central Illinois

KEY MESSAGES

- Improving Air Quality: Wildfire smoke from Canada will cause hazy conditions and reduced air quality across central Illinois today. Southerly winds are expected to clear the plume northeastward by this evening, bringing noticeable relief.

- Severe Storms Tonight: There remains moderate confidence for a severe weather threat primarily after midnight tonight. An organized line of storms is expected to move southeastward, with a primary threat of damaging downburst winds.

- Lingering Storm Threat Tuesday in Southeast IL: A slowing cold front keeps a lower confidence threat of storms in southeast Illinois through Tuesday afternoon. Quieter, cooler, and more comfortable weather arrives statewide by Wednesday.

DISCUSSION

Issued at 240 AM CDT Mon Jul 20 2026

Smoke and Air Quality...

Wildfire smoke will linger for another day across central IL, however relief is on the horizon. A warm frontal boundary will lift northward through the region today, causing a wind shift to the S-SW. This transition will facilitate the clearing of the plume, pushing it northeastward and allowing for improving air quality conditions across the area by this evening.

Severe Weather Outlook: Today and Tonight

Several CAMs are propagating the ongoing complex of storms in west-central Minnesota into our NW CWA by early afternoon. There is support for that scenario as bulk shear values climb toward 35KT this afternoon. However, the consensus of high resolution models have that complex diminishing before reaching the IL River Valley. So the chances of severe weather with that initial storm system appear low. The primary focus for severe storms with the Day 1 outlook will be after midnight tonight. Forecast soundings indicate robust destabilization, with MLCAPE values peaking near 2500 J/kg. This instability will coincide with a potent jet stream impulse digging into the Upper Midwest, driving a significant increase in deep-layer shear. Projections of 40-50kt of 0-6km bulk shear suggest a favorable environment for organized convective systems.

Convective initiation is anticipated over the Upper Midwest by this afternoon, driven by an approaching shortwave trough. The storm mode should transition into a more organized cluster or line as it propagates southeastward during the mid-to-late evening. A strengthening low-level jet will be critical in sustaining this activity as it traverses the instability gradient across central Illinois. Given the overlap of instability and shear, this period remains the primary window of concern for severe thunderstorms, and we will continue to monitor the mesoscale evolution closely.

Storm Chances and Severe Potential: Tuesday

A slowing trend in the cold frontal movement will set the stage for lingering severe weather potential on Tuesday. There are indications of a flare-up of storms in the post frontal airmass across SE IL, but high uncertainty remains on coverage of those storms. A more limited shear and instability profile than Monday night should limit severe potential somewhat. That complex of storms should push southeast of our CWA by late Tuesday.

Extended Forecast: Wednesday through the Weekend

A welcome shift toward quieter, more seasonal weather arrives mid- week. Beginning Wednesday, a sprawling Canadian high-pressure system will settle into the Midwest, ushering in a drier airmass and providing relief from the recent heat. Expect comfortable temperatures topping out in the low to mid-80s, with a dry forecast prevailing through the remainder of the work week. As the surface ridge axis drifts to our east next weekend, a gradual warming trend will commence, bringing a return of warmer southerly flow.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 544 AM CDT Mon Jul 20 2026

Smoky conditions will persist this morning, with visibility as low as 3SM to 4SM at all TAF sites. However, improvement is likely this afternoon as winds shift to southwest behind a northward moving warm front. That should push the smoke to the northeast. A storm complex in SE MN at 10Z this morning is projected to hold together until it reaches near PIA toward 17Z. Model consensus shows the storm dissipating quickly as it crosses the Illinois River. After that, some scattered mid clouds will occur this afternoon with a few CU. More widespread coverage of storms is projected for between 06z and 12z overnight, as a squall line advances from NW to SE across central IL. A few strong downburst winds are possible with that complex, especially toward PIA and BMI. Winds will shift from SW to W after the overnight storms depart to the south.

ILX WATCHES/WARNINGS/ADVISORIES

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