Area Forecast Discussion

KEY MESSAGES

- One last day with dangerous heat and humidity is forecast on Tuesday along/south of I-70.

- A few strong to severe storms are possible with damaging through late this evening in parts of south-central Illinois.

- Widespread heat relief is expected by Wednesday, with near normal temperatures through the end of the work week.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 239 PM CDT Mon Jul 27 2026

Dangerous heat and humidity remains the main story today with temperatures climbing well into the mid 90s as of 2 PM. A few spots today may touch the century mark. Dewpoints are still unseasonably high as well (~90th percentile), though are an improvement compared to yesterday. Heat index values are mostly in the 105-110F range, and may come up another couple of degrees later this afternoon.

Chances of showers and thunderstorms is the next concern through this evening. Ongoing severe convection near and just southeast of Chicago should continue to move south/southeast and stay away from our region. There have been some subtle signs at development farther west into western Illinois over the past 1-2 hours. GOES-19 also is showing a westward-propagating gravity wave, which could also impact convective initiation over the next 1-2 hours. IF storms can develop and strengthen, they may clip our south-central Illinois counties this evening. Damaging winds would be the main threat if any storms move into our region. Finally, there is some weaker elevated convection as far west as the Missouri River near the NE/IA border. These storms have been on/off nearly all day and have never been able to move much southeast due to strong capping. The expectation is for this cap to continue to help shield central/northeast Missouri from these storms making it into the area.

The synoptic cold front is expected to move southward slowly overnight tonight through Tuesday morning. This boundary may help serve the focus for a few isolated (weaker) thunderstorms with as a weak low-level jet strengthens overnight. A better chance (30%) of showers and a few storms comes late morning through the evening hours on Tuesday as a midlevel shortwave trough ejects out of the mid-Missouri Valley. This activity looks to be behind the synoptic cold front and elevated in nature. Strong to severe storms are therefore not likely as the threat for damaging winds with elevated convection is quite low and chances of severe hail making it to the surface also very low.

Dangerous heat/humidity remains a top concern on Tuesday, though the threat area will shift more to the south and out of areas north of I- 70. Lingering high dewpoints though north of the cold front will still make it feel like 100-105+ for those along/south of I-70. Where 105+ values are expected once again, continued the heat warning another day with an advisory to the north for locations where peak heat index values of 100-105F are forecast.

LONG TERM /WEDNESDAY THROUGH MONDAY/

Issued at 239 PM CDT Mon Jul 27 2026

Dry weather with near normal temperatures is forecast Wednesday through Thursday thanks in part due to a weak ridge of surface high pressure across the area. We are still looking for a good chance (50- 70%) of showers and thunderstorms from a potential MCS Thursday night - Friday night. Ensemble guidance has shifted a bit more toward a slower midlevel trough passage this weekend, with a minority (23%) of members from the LREF showing a cutoff midlevel low. This means a couple of things, but namely: 1) cooler daytime temperatures Friday through next weekend and 2) lingering rain chances.

AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1040 PM CDT Mon Jul 27 2026

VFR conditions are expected to continue overnight with a cold front dropping north to south across the region. By morning, most locations will see winds with a northerly component, becoming more NNE as the day goes on. Thunderstorms are finished for now, but the next round is expected to get going over western Missouri overnight tonight. Latest CAMs are consistent in keeping this activity just west of our region on Tuesday, but central Missouri TAF sites will be closest to this action and have the best chance of being affected. This chance is too low to include in the TAF at this time.

LSX WATCHES / WARNINGS / ADVISORIES

MO...Heat Advisory until 7 PM CDT Tuesday for MOZ041-047>052- 059>064. Extreme Heat Warning until 7 PM CDT Tuesday for MOZ065-072>075- 084-085-099. IL...Heat Advisory until 7 PM CDT Tuesday for ILZ064-069-070-100. Extreme Heat Warning until 7 PM CDT Tuesday for ILZ074-079-101- 102.