National Oceanic and Atmospheric Administration National Weather Service United States Department of Commerce
Current conditions at

St. Louis Downtown Airport (KCPS)

Lat: 38.56°NLon: 90.15°WElev: 410ft.

Partly Cloudy

83°F

28°C

Humidity 40%
Wind Speed Calm
Barometer 29.99 in (1015.2 mb)
Dewpoint 56°F (13°C)
Visibility 10.00 mi
Heat Index82°F (28°C)
Last update 19 Jun 5:53 pm CDT
Extended Forecast for

O'Fallon IL

  • Tonight

    Tonight: Mostly cloudy, with a low around 65. Calm wind.

    Low: 65 °F

    Mostly Cloudy

  • Saturday

    Saturday: A 20 percent chance of showers before 10am. Mostly sunny, with a high near 85. Calm wind becoming north around 5 mph.

    High: 85 °F

    Slight Chance
    Showers then
    Mostly Sunny

  • Saturday Night

    Saturday Night: A slight chance of showers between 1am and 5am, then a chance of showers and thunderstorms after 5am. Mostly cloudy, with a low around 68. Calm wind becoming east around 5 mph after midnight. Chance of precipitation is 30%.

    Low: 68 °F

    Partly Cloudy
    then Chance
    Showers

  • Sunday

    Sunday: Showers and thunderstorms, mainly after 7am. High near 82. Southeast wind 6 to 15 mph becoming southwest in the afternoon. Winds could gust as high as 24 mph. Chance of precipitation is 90%.

    High: 82 °F

    T-storms

  • Sunday Night

    Sunday Night: Showers and thunderstorms, mainly before 1am. Low around 67. Southwest wind 9 to 11 mph becoming northwest after midnight. Chance of precipitation is 90%.

    Low: 67 °F

    T-storms

  • Monday

    Monday: A 20 percent chance of showers and thunderstorms before 1pm. Partly sunny, with a high near 78.

    High: 78 °F

    Slight Chance
    T-storms

  • Monday Night

    Monday Night: Partly cloudy, with a low around 62.

    Low: 62 °F

    Partly Cloudy

  • Tuesday

    Tuesday: Mostly sunny, with a high near 80.

    High: 80 °F

    Mostly Sunny

  • Tuesday Night

    Tuesday Night: A 20 percent chance of showers after 1am. Partly cloudy, with a low around 63.

    Low: 63 °F

    Partly Cloudy
    then Slight
    Chance
    Showers

Detailed Forecast

Tonight
Mostly cloudy, with a low around 65. Calm wind.
Saturday
A 20 percent chance of showers before 10am. Mostly sunny, with a high near 85. Calm wind becoming north around 5 mph.
Saturday Night
A slight chance of showers between 1am and 5am, then a chance of showers and thunderstorms after 5am. Mostly cloudy, with a low around 68. Calm wind becoming east around 5 mph after midnight. Chance of precipitation is 30%.
Sunday
Showers and thunderstorms, mainly after 7am. High near 82. Southeast wind 6 to 15 mph becoming southwest in the afternoon. Winds could gust as high as 24 mph. Chance of precipitation is 90%.
Sunday Night
Showers and thunderstorms, mainly before 1am. Low around 67. Southwest wind 9 to 11 mph becoming northwest after midnight. Chance of precipitation is 90%.
Monday
A 20 percent chance of showers and thunderstorms before 1pm. Partly sunny, with a high near 78.
Monday Night
Partly cloudy, with a low around 62.
Tuesday
Mostly sunny, with a high near 80.
Tuesday Night
A 20 percent chance of showers after 1am. Partly cloudy, with a low around 63.
Wednesday
Mostly sunny, with a high near 82.
Wednesday Night
Mostly clear, with a low around 63.
Thursday
A 20 percent chance of showers and thunderstorms. Mostly sunny, with a high near 81.
Thursday Night
A 30 percent chance of showers and thunderstorms. Partly cloudy, with a low around 64.
Friday
A 30 percent chance of showers and thunderstorms. Mostly sunny, with a high near 82.
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Forecast Area
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ABOUT THIS FORECAST

 
Point Forecast:
O'Fallon IL
 38.59°N 89.95°W (Elev. 545 ft)
Last Update:
6:01 pm CDT Jun 19, 2026
Forecast Valid:
6pm CDT Jun 19, 2026-6pm CDT Jun 26, 2026
 
Forecast Discussion
 
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Additional Resources

Radar & Satellite Image

Link to Local Radar Data Link to Satellite Data

Hourly Weather Forecast

National Digital Forecast Database

National Digital Forecast Database Maximum Temperature Forecast

High Temperature

National Digital Forecast Database Weather Element Forecast

Chance of Precipitation