textproduct: Central Illinois

KEY MESSAGES

- Wildfire Smoke and Poor Air Quality Today: Thick wildfire smoke will bring widespread hazy skies and degraded air quality through midnight tonight. Visibility will be diminished as air quality reaches to unhealthy levels for sensitive groups.

- Severe Weather Risk Monday Night: While the higher threat for severe storms will be northwest of central Illinois, areas north of I-72 will have a threat for damaging downburst winds and locally heavy rainfall Monday evening.

- Dry and Cooler Late Week: A strong high-pressure system will bring a return to quiet weather from Wednesday through Friday. Expect dry conditions with comfortable, slightly below-normal temperatures in the upper 70s to lower 80s.

DISCUSSION

Issued at 252 AM CDT Sun Jul 19 2026

Synopsis... The surface cold front responsible for last evenings convective activity has progressed southward to near the I-72 corridor as of 06z (1 AM CDT). While post-frontal airmass modification has been sluggish initially, a robust Canadian high-pressure system will build southward over the Upper Midwest today. This feature will effectively drive the boundary south of the forecast area, delivering a temporary period of cooler, but noticeably hazy conditions. The primary near-term concern centers around a significant plume of near-surface wildfire smoke accompanying this high. Looking ahead, the frontal boundary will lift back northward as a warm front on Monday, setting the stage for a volatile thermodynamic environment and a growing threat for organized severe weather late Monday into Monday night. Quieter, cooler, and highly comfortable conditions return by mid-to-late week.

Today and Tonight: Wildfire Smoke & Air Quality Impacts. The main story for today is the incoming surge of vertically integrated and near-surface smoke originating from Canadian wildfires. Upstream observations across northern Illinois have already noted visibility restrictions dropping into the 2 to 5-mile range.

High-resolution smoke transport modeling (HRRR and RRFS) bring this thick smoke plume southwestward across central Illinois through the morning and afternoon hours. While some discrepancies exist regarding concentrations with the HRRR exhibiting a lower impacts compared to the more aggressive RRFS. Our forecast leans toward a more pessimistic, smoke-laden outcome. This aligns closely with recent upstream trends. Expect widespread hazy skies and degraded air quality capable of reaching Unhealthy for Sensitive Groups (USG) thresholds. Consequently, the Air Quality Alert remains in effect for the entire CWA through midnight tonight.

Otherwise, expect a dry day with high temperatures held in the low to mid-80s due to a mix of weak cold advection and solar attenuation from the smoke layer. Smoke concentrations should gradually decrease overnight as the surface high slides eastward.

Monday Severe Weather Potential... On Monday, the upstream pattern shifts rapidly as a potent shortwave trough ejects across the Northern Plains, forcing the stalled surface front to lift back northward as a warm front. Deep southerly to south-westerly flow will re-establish in its wake, transporting a highly unstable airmass characterized by upper 80s to lower 90s surface temperatures and pooling dewpoints in the low 70s.

Confidence is steadily increasing in a multi-hazard severe weather episode late Monday afternoon into Monday night, with a higher potential in NW IL and points NW of there. As a strong cold front approaches from the northwest, intense destabilization combined with 3545 knots of mid-level westerly flow will provide sufficient deep-layer shear to organize convection. Initial discrete or semi-discrete development along and ahead of the front west of Illinois will likely upscale into a forward-propagating mesoscale convective system (MCS) or squall line as it sweeps southeastward into our region.

Primary Hazards: Damaging straight-line winds look to be the predominant threat given steep low-level lapse rates and high DCAPE potential. However, large hail and a few tornadoes cannot be ruled out, particularly with any initial discrete structures or along the QLCS.

Heavy Rainfall: Precipitable Water (PWAT) values climbing near or above 2.0 inches will support highly efficient rainfall rates. Locally heavy rain could lead to localized flash flooding, especially in areas seeing repeated convective tracks.

By Wednesday, a sprawling, high-amplitude Canadian high- pressure system will anchor itself over the Great Lakes and Midwest regions. This will usher in an extended period of exceptionally quiet and comfortable weather. Deep north-to- northeasterly flow will reinforce a dry airmass, dropping dewpoints back into the more comfortable 50s. High temperatures from Wednesday through Friday will average slightly below normal, comfortably topping out in the upper 70s to mid-80s under mostly clear skies. This beautiful mid-summer stretch looks to persist well into the upcoming weekend before the high begins to shift eastward.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 627 AM CDT Sun Jul 19 2026

Smoke has moved into the area and will likely remain until Tuesday morning. Band of broken to overcast CU/SC remains over the central part affecting SPI, DEC, and CMI. However, do not believe this will last all day so scatter them out around 15z. BMI and CMI have dropped to 2sm, but believe this evening, they both will improve to 3sm. Though not at SPI yet, believe they will see vis drop very soon, so have PIA, SPI, and DEC at 3sm through the period. Winds will be easterly at 10kts or less through the day and then becoming light and variable this evening.

ILX WATCHES/WARNINGS/ADVISORIES

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