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

Thunderstorms and Heavy Rainfall in the Southeast, Montana, and Iowa; Lowell Begins to Impact Hawaii

Strong thunderstorms with damaging winds and heavy rain are expected across portions of the Southeast. Thunderstorms may produce large hail across portions of Montana. Heavy rainfall could produce flash flooding across Iowa and vulnerable areas in Utah. Lowell will bring heavy rain, dangerous swells and rip currents to portions of Hawaii. Sweltering heat persists across the South-Central US. Read More >

Current conditions at

St. Louis Downtown Airport (KCPS)

Lat: 38.56°NLon: 90.15°WElev: 410ft.

A Few Clouds

89°F

32°C

Humidity 52%
Wind Speed N 3 mph
Barometer 29.95 in (1013.8 mb)
Dewpoint 69°F (21°C)
Visibility 10.00 mi
Heat Index94°F (34°C)
Last update 6 Sep 3:53 pm CDT
Extended Forecast for

O'Fallon IL

  • Tonight

    Tonight: Mostly clear, with a low around 65. East wind 6 to 11 mph.

    Low: 65 °F

    Mostly Clear

  • Labor Day

    Labor Day: Sunny, with a high near 90. East wind 5 to 8 mph.

    High: 90 °F

    Sunny

  • Monday Night

    Monday Night: Partly cloudy, with a low around 65. East wind around 6 mph becoming calm after midnight.

    Low: 65 °F

    Partly Cloudy

  • Tuesday

    Tuesday: Mostly sunny, with a high near 96. Calm wind becoming south around 6 mph in the morning.

    High: 96 °F

    Mostly Sunny

  • Tuesday Night

    Tuesday Night: Mostly clear, with a low around 73. South wind 5 to 10 mph.

    Low: 73 °F

    Mostly Clear

  • Wednesday

    Wednesday: Mostly sunny and hot, with a high near 98.

    High: 98 °F

    Hot

  • Wednesday Night

    Wednesday Night: Showers and possibly a thunderstorm. Low around 70. Chance of precipitation is 80%.

    Low: 70 °F

    Showers

  • Thursday

    Thursday: A 50 percent chance of showers and thunderstorms before 1pm. Mostly cloudy, with a high near 85.

    High: 85 °F

    Chance
    Showers

  • Thursday Night

    Thursday Night: A 20 percent chance of showers before 1am. Partly cloudy, with a low around 64.

    Low: 64 °F

    Slight Chance
    Showers

Detailed Forecast

Tonight
Mostly clear, with a low around 65. East wind 6 to 11 mph.
Labor Day
Sunny, with a high near 90. East wind 5 to 8 mph.
Monday Night
Partly cloudy, with a low around 65. East wind around 6 mph becoming calm after midnight.
Tuesday
Mostly sunny, with a high near 96. Calm wind becoming south around 6 mph in the morning.
Tuesday Night
Mostly clear, with a low around 73. South wind 5 to 10 mph.
Wednesday
Mostly sunny and hot, with a high near 98.
Wednesday Night
Showers and possibly a thunderstorm. Low around 70. Chance of precipitation is 80%.
Thursday
A 50 percent chance of showers and thunderstorms before 1pm. Mostly cloudy, with a high near 85.
Thursday Night
A 20 percent chance of showers before 1am. Partly cloudy, with a low around 64.
Friday
Sunny, with a high near 87.
Friday Night
A 30 percent chance of showers and thunderstorms. Mostly clear, with a low around 65.
Saturday
A 30 percent chance of showers. Mostly sunny, with a high near 91.
Saturday Night
A 30 percent chance of showers and thunderstorms. Mostly clear, with a low around 68.
Sunday
A 30 percent chance of showers and thunderstorms. Mostly sunny, with a high near 89.
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Forecast Area
Tiles ©ESRI

ABOUT THIS FORECAST

 
Point Forecast:
O'Fallon IL
 38.59°N 89.89°W (Elev. 541 ft)
Last Update:
2:26 pm CDT Sep 6, 2026
Forecast Valid:
3pm CDT Sep 6, 2026-6pm CDT Sep 13, 2026
 
Forecast Discussion
 
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Additional Resources

Radar & Satellite Image

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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