textproduct: Central Illinois

KEY MESSAGES

- Hot and humid weather with peak afternoon heat index readings of 100 to 110 will continue through Friday, and will likely reach 100 to 105 on Saturday afternoon, highest in southeast IL.

- A low risk for severe weather exists both Friday and Saturday. The highest probability (15-30% chance) for scattered damaging wind gusts will focus along/north of a Peoria to Pontiac line Friday afternoon and evening.

- There is a Marginal Risk (5-15% chance) for excessive rainfall with some of the thunderstorms this weekend...particularly on Saturday.

DISCUSSION

Issued at 400 AM CDT Thu Jul 2 2026

**** Heat and Humidity ****

Typical summertime heat and humidity will continue into the first part of the holiday weekend. Heat index readings will peak at 105-110 degrees along/south of the I-72 corridor both today and Friday. After that, increasing cloud cover and thunderstorm chances will lead to a gradual easing of the heat over the weekend. As upper ridging shifts westward and re-establishes over the Desert Southwest, weak W/NW flow across the Midwest will help drop air temperatures back to seasonal normals in the middle to upper 80s Sunday through Wednesday.

**** Low Severe Weather Risk Friday and Saturday ****

As the upper flow pattern becomes zonal, a series of short-wave troughs will trigger several rounds of convection across parts of the region Friday through Sunday. With surface dewpoints remaining in the middle to upper 70s, SBCAPE values will exceed 3000J/kg both Friday and Saturday afternoons. While the atmosphere will be moist and strongly unstable, deep-layer shear will be largely absent as evidenced by NAM 0-6km bulk shear values of just 20-25kt. A short-wave and/or MCV is expected to track from South Dakota/Nebraska into the southern Great Lakes on Friday, enhancing shear values across Wisconsin and northern Illinois where severe probabilities have been increased to 15-30%. North-central Illinois will be on the southern fringe of the better shear, so am expecting minimal widespread storm organization. Several CAMs including the 00z RRFS show a cluster of thunderstorms forming in advance of the MCV across eastern Iowa/northwestern Illinois toward midday Friday, then tracking eastward through the Chicago area during the afternoon. Some of these cells will likely develop further south into the highly unstable airmass across central Illinois...posing a risk for a few damaging wind gusts with the strongest storms along/north of the I-72 corridor. Further north from the Peoria area northward, the risk for severe is a bit higher...but still limited by the overall lack of shear. An outflow boundary will settle southward on Saturday, leading to a higher probability (40-70% chance) of showers and thunderstorms across all of central Illinois. A Marginal Risk (level 1 of 5) for severe weather exists as a few of the cells may be capable of damaging wind gusts. Scattered thunderstorms will continue mainly east of the I-55 corridor on Sunday: however, decreasing instability will lead to an even lower severe risk at that time.

While the holiday weekend will not be a complete wash-out, central Illinois residents should keep a close eye on the forecast and be aware that some outdoor activities may be impacted.

**** Pockets of Heavy Rainfall This Weekend ****

With surface dewpoints hovering in the middle to upper 70s and precipitable water values increasing to 1.75-2.25, thunderstorms will be efficient rain-producers this weekend. In addition, slow storm movement will allow some of the stronger cells to drop heavy rainfall. While not all locations will get heavy rain, a few spots may experience excessive rainfall rates that lead to localized flash flooding. As a result, WPC has highlighted all of central and southeast Illinois with a Marginal Risk (5-15% chance) of excessive rainfall on Saturday.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1235 PM CDT Thu Jul 2 2026

VFR conditions will prevail through much of the 18Z TAF period for the central IL airports. Scattered to occasionally broken diurnal cumulus clouds (broken ceilings more likely along I-74) with bases of 2-4k ft this afternoon will likely redevelop after 15Z/10 am Friday. Latest CAMs show bands of showers and thunderstorms developing and moving over northern/nw IL during this evening and getting close to PIA between 05-09Z where VCTS added. Will need to watch if this convection gets as far se as BMI overnight after 08Z/3 am. SW winds near 10 kts with few gusts 15-20 kts this afternoon at PIA and BMI, to be south at 4-8 kts after sunset and SW at 7-10 kts after 15Z/10 am Friday.

ILX WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until midnight CDT tonight for ILZ027>031- 036>038-041. Extreme Heat Warning until 7 PM CDT Friday for ILZ040-042>057- 061>063-066>068-071>073.