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

Dangerous Heat over the South-Central and Southwest U.S. Through Next Week

Dangerous heat persists across the Desert Southwest through this weekend and across the Southern Plains and Lower Mississippi Valley through at least the middle of next week. Numerous daily record high temperatures are expected through at least Tuesday for much of Texas and Oklahoma as well as portions of Louisiana, New Mexico, and Arizona. Read More >

Current conditions at

St. Louis Downtown Airport (KCPS)

Lat: 38.56°NLon: 90.15°WElev: 410ft.

Partly Cloudy

73°F

23°C

Humidity 76%
Wind Speed N 6 mph
Barometer 30.05 in (1017.2 mb)
Dewpoint 65°F (18°C)
Visibility 10.00 mi
Last update 23 Aug 12:53 am CDT
Extended Forecast for

O'Fallon IL

  • Overnight

    Overnight: Mostly clear, with a low around 64. Light north wind.

    Low: 64 °F

    Mostly Clear

  • Sunday

    Sunday: Increasing clouds, with a high near 82. Northwest wind 3 to 8 mph.

    High: 82 °F

    Increasing
    Clouds

  • Sunday Night

    Sunday Night: Mostly cloudy, then gradually becoming mostly clear, with a low around 61. North wind around 5 mph becoming calm in the evening.

    Low: 61 °F

    Decreasing
    Clouds

  • Monday

    Monday: Increasing clouds, with a high near 82. Calm wind becoming southeast around 5 mph in the afternoon.

    High: 82 °F

    Increasing
    Clouds

  • Monday Night

    Monday Night: Partly cloudy, with a low around 64. East wind around 5 mph becoming calm in the evening.

    Low: 64 °F

    Partly Cloudy

  • Tuesday

    Tuesday: Mostly sunny, with a high near 84.

    High: 84 °F

    Mostly Sunny

  • Tuesday Night

    Tuesday Night: Partly cloudy, with a low around 68.

    Low: 68 °F

    Partly Cloudy

  • Wednesday

    Wednesday: Mostly sunny, with a high near 88.

    High: 88 °F

    Mostly Sunny

  • Wednesday Night

    Wednesday Night: A 20 percent chance of showers and thunderstorms before 1am. Mostly clear, with a low around 69.

    Low: 69 °F

    Slight Chance
    T-storms

Detailed Forecast

Overnight
Mostly clear, with a low around 64. Light north wind.
Sunday
Increasing clouds, with a high near 82. Northwest wind 3 to 8 mph.
Sunday Night
Mostly cloudy, then gradually becoming mostly clear, with a low around 61. North wind around 5 mph becoming calm in the evening.
Monday
Increasing clouds, with a high near 82. Calm wind becoming southeast around 5 mph in the afternoon.
Monday Night
Partly cloudy, with a low around 64. East wind around 5 mph becoming calm in the evening.
Tuesday
Mostly sunny, with a high near 84.
Tuesday Night
Partly cloudy, with a low around 68.
Wednesday
Mostly sunny, with a high near 88.
Wednesday Night
A 20 percent chance of showers and thunderstorms before 1am. Mostly clear, with a low around 69.
Thursday
Sunny, with a high near 87.
Thursday Night
Mostly clear, with a low around 66.
Friday
Sunny, with a high near 85.
Friday Night
A 20 percent chance of showers. Partly cloudy, with a low around 66.
Saturday
A 20 percent chance of showers. Mostly sunny, with a high near 86.
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Forecast Area
Tiles ©ESRI

ABOUT THIS FORECAST

 
Point Forecast:
O'Fallon IL
 38.59°N 89.92°W (Elev. 551 ft)
Last Update:
1:26 am CDT Aug 23, 2026
Forecast Valid:
1am CDT Aug 23, 2026-6pm CDT Aug 29, 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