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O'Fallon Weather Forecast
| TONIGHT | LABOR DAY | MONDAY NIGHT | TUESDAY | TUESDAY NIGHT | WEDNESDAY | WEDNESDAY NIGHT | THURSDAY | THURSDAY NIGHT | FRIDAY | FRIDAY NIGHT | SATURDAY |
 |  |  | | |  |  | |  | | | |
| Partly Cloudy | Sunny | Mostly Clear | Mostly Sunny | Mostly Clear | Chance of T-Storm | Chance of T-Storm | Chance of T-Storm | Chance of Showers | Sunny | Chance of T-Storm | Chance of T-Storm |
| 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 | Hi: 90°FHi: 32°C |
| POP: 20% | POP: 80% | POP: 50% | POP: 20% | POP: 30% | POP: 30% |
POP = Probability of Precipitation.
Weather Outlook Updated: 938 PM CDT Sun Sep 06 2026 
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Issued: 625 PM CDT Sun Sep 6 2026
Key Messages
- Less humid air is in store for Labor Day before a (brief) return to well-above normal temperatures Tuesday through Wednesday.
Aviation
/00Z TAFS THROUGH 06Z TUESDAY/... Issued at 619 PM CDT Sun Sep 6 2026
VFR flight conditions and light easterly flow is expected to prevail through Monday. Some river valley fog is possible before sunrise, mainly across the eastern Ozarks. The probability of fog is low though (less than 30 percent) due to drier air moving into the area and high clouds blo...