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O'Fallon Weather Forecast
| THIS AFTERNOON | TONIGHT | LABOR DAY | MONDAY NIGHT | TUESDAY | TUESDAY NIGHT | WEDNESDAY | WEDNESDAY NIGHT | THURSDAY | THURSDAY NIGHT | FRIDAY | FRIDAY NIGHT |
 |  | | | |  |  |  | |  | | |
| Sunny | Partly Cloudy | Sunny | Partly Cloudy | Mostly Sunny | Mostly Clear | Chance of T-Storm | Chance of T-Storm | Chance of T-Storm | Chance of Showers | Sunny | Chance of T-Storm |
| Hi: 90°FHi: 32°C | Lo: 65°FLo: 18°C | Hi: 90°FHi: 32°C | Lo: 65°FLo: 18°C | Hi: 95°FHi: 35°C | Lo: 71°FLo: 22°C | Hi: 99°FHi: 37°C | Lo: 69°FLo: 21°C | Hi: 85°FHi: 29°C | Lo: 61°FLo: 16°C | Hi: 85°FHi: 29°C | Lo: 65°FLo: 18°C |
| POP: 20% | POP: 80% | POP: 50% | POP: 20% | POP: 30% |
POP = Probability of Precipitation.
Weather Outlook Updated: 127 PM CDT Sun Sep 06 2026 
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Issued: 1225 PM CDT Sun Sep 6 2026
Key Messages
- Another day of heat index values around 100 F is forecast for central and southeastern MO, but cooler temperatures and lower humidity will arrive elsewhere today, becoming areawide by Monday.
- Heat and near-record breaking temperatures will briefly return Tuesday into Wednesday.
Aviation
/18Z TAFS THROUGH 00Z TUESDAY/... Issued at 1222 PM CDT Sun Sep 6 2026
The NW-SE oriented stratus is quickly scattering as low-level dry air is advecting in from the northeast. VFR conditions are expecte...