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

Dangerous Heat and Heavy Rainfall into the Weekend

Hot temperatures and high humidity are forecast to continue across the mid-Mississippi Valley into this weekend. Heat Advisories remain in effect. Heavy to excessive rainfall occurring at times through the weekend could bring areas of flooding to parts of the northern Rockies, upper Midwest, central Great Lakes, and southern New England. Read More >

Hazardous Weather Conditions

Current conditions at

St. Louis, Spirit Of St. Louis Airport (KSUS)

Lat: 38.66°NLon: 90.66°WElev: 463ft.

Fair with Haze

85°F

29°C

Humidity 53%
Wind Speed SW 13 mph
Barometer 29.97 in (1013.9 mb)
Dewpoint 66°F (19°C)
Visibility 6.00 mi
Heat Index87°F (31°C)
Last update 19 Sep 9:54 am CDT
Extended Forecast for

O'Fallon MO

Heat Advisory September 19, 10:08am until September 19, 08:00pm
Click here for hazard details and duration
Heat Advisory
  •  
    Heat Advisory September 19, 10:08am until September 19, 08:00pm

    NOW until 8:00pm Sat

    Heat Advisory

  • Today

    High: 96 °F

    Partly Sunny

  • Tonight

    Tonight: Partly cloudy, with a low around 72. Calm wind becoming southwest around 5 mph after midnight.

    Low: 72 °F

    Partly Cloudy

  • Sunday

    Sunday: A chance of showers before noon, then a slight chance of showers and thunderstorms after 4pm. Partly sunny, with a high near 90. Calm wind becoming northwest around 5 mph in the afternoon. Chance of precipitation is 40%.

    High: 90 °F

    Chance
    Showers then
    Slight Chance
    T-storms

  • Sunday Night

    Sunday Night: A chance of showers and thunderstorms, then showers likely and possibly a thunderstorm after 1am. Mostly cloudy, with a low around 66. Northeast wind 5 to 7 mph. Chance of precipitation is 70%.

    Low: 66 °F

    Chance
    T-storms then
    Showers
    Likely

  • Monday

    Monday: Showers likely and possibly a thunderstorm before 10am, then showers likely between 10am and 1pm, then a chance of showers and thunderstorms after 1pm. Mostly cloudy, with a high near 75. Northeast wind 6 to 9 mph. Chance of precipitation is 60%.

    High: 75 °F

    Showers
    Likely

  • Monday Night

    Monday Night: A 20 percent chance of showers. Mostly cloudy, with a low around 58.

    Low: 58 °F

    Slight Chance
    Showers

  • Tuesday

    Tuesday: Mostly cloudy, with a high near 69.

    High: 69 °F

    Mostly Cloudy

  • Tuesday Night

    Tuesday Night: Mostly cloudy, with a low around 53.

    Low: 53 °F

    Mostly Cloudy

Detailed Forecast

Today
Partly sunny, with a high near 96. Heat index values as high as 100. West wind around 7 mph.
Tonight
Partly cloudy, with a low around 72. Calm wind becoming southwest around 5 mph after midnight.
Sunday
A chance of showers before noon, then a slight chance of showers and thunderstorms after 4pm. Partly sunny, with a high near 90. Calm wind becoming northwest around 5 mph in the afternoon. Chance of precipitation is 40%.
Sunday Night
A chance of showers and thunderstorms, then showers likely and possibly a thunderstorm after 1am. Mostly cloudy, with a low around 66. Northeast wind 5 to 7 mph. Chance of precipitation is 70%.
Monday
Showers likely and possibly a thunderstorm before 10am, then showers likely between 10am and 1pm, then a chance of showers and thunderstorms after 1pm. Mostly cloudy, with a high near 75. Northeast wind 6 to 9 mph. Chance of precipitation is 60%.
Monday Night
A 20 percent chance of showers. Mostly cloudy, with a low around 58.
Tuesday
Mostly cloudy, with a high near 69.
Tuesday Night
Mostly cloudy, with a low around 53.
Wednesday
Mostly sunny, with a high near 72.
Wednesday Night
Partly cloudy, with a low around 54.
Thursday
Mostly sunny, with a high near 74.
Thursday Night
Mostly cloudy, with a low around 57.
Friday
Partly sunny, with a high near 76.
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Forecast Area
Tiles ©ESRI

ABOUT THIS FORECAST

 
Point Forecast:
O'Fallon MO
 38.79°N 90.74°W (Elev. 597 ft)
Last Update:
7:56 am CDT Sep 19, 2026
Forecast Valid:
10am CDT Sep 19, 2026-6pm CDT Sep 25, 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