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

Areas of Dangerous Heat and Heavy Rain with Possible Flooding into this Weekend

Hot temperatures and high humidity are forecast to continue across the mid-Mississippi Valley into this weekend with heat advisories in effect. Heavy to excessive rainfall occurring at times through Sunday could bring areas of flooding to parts of the upper Midwest, central Great Lakes, southern New England and Virginia/North Carolina tidewater region. Read More >

Hazardous Weather Conditions

Current conditions at

St. Louis Downtown Airport (KCPS)

Lat: 38.56°NLon: 90.15°WElev: 410ft.

Fair

74°F

23°C

Humidity 94%
Wind Speed Calm
Barometer 30.14 in (1020.0 mb)
Dewpoint 72°F (22°C)
Visibility 10.00 mi
Last update 18 Sep 2:53 am CDT
Extended Forecast for

Swansea IL

Heat Advisory September 18, 03:45am until September 19, 08:00pm
Click here for hazard details and duration
Heat Advisory
  •  
    Heat Advisory September 18, 03:45am until September 19, 08:00pm

    NOW until 8:00pm Sat

    Heat Advisory

  • Overnight

    Low: 73 °F

    Mostly Clear

  • Friday

    Friday: A slight chance of showers between 2pm and 4pm, then a slight chance of showers and thunderstorms after 4pm. Sunny, with a high near 96. Heat index values as high as 107. Calm wind becoming north around 5 mph. Chance of precipitation is 20%.

    High: 96 °F

    Sunny then
    Slight Chance
    T-storms

  • Friday Night

    Friday Night: A 20 percent chance of showers and thunderstorms before 11pm. Partly cloudy, with a low around 72. Light and variable wind becoming east around 6 mph in the evening.

    Low: 72 °F

    Slight Chance
    T-storms then
    Partly Cloudy

  • Saturday

    Saturday: Increasing clouds, with a high near 96. Heat index values as high as 101. South wind 5 to 7 mph becoming west in the afternoon.

    High: 96 °F

    Increasing
    Clouds

  • Saturday Night

    Saturday Night: Partly cloudy, with a low around 73. Calm wind becoming south around 5 mph after midnight.

    Low: 73 °F

    Partly Cloudy

  • Sunday

    Sunday: A slight chance of showers between 1pm and 4pm, then a slight chance of showers and thunderstorms after 4pm. Mostly sunny, with a high near 93. Chance of precipitation is 20%.

    High: 93 °F

    Mostly Sunny
    then Slight
    Chance
    T-storms

  • Sunday Night

    Sunday Night: A 50 percent chance of showers and thunderstorms, mainly after 1am. Mostly cloudy, with a low around 68.

    Low: 68 °F

    Slight Chance
    T-storms then
    Chance
    T-storms

  • Monday

    Monday: Showers likely, with thunderstorms also possible after 1pm. Mostly cloudy, with a high near 83. Chance of precipitation is 70%.

    High: 83 °F

    Showers
    Likely

Detailed Forecast

Overnight
Mostly clear, with a low around 73. Calm wind.
Friday
A slight chance of showers between 2pm and 4pm, then a slight chance of showers and thunderstorms after 4pm. Sunny, with a high near 96. Heat index values as high as 107. Calm wind becoming north around 5 mph. Chance of precipitation is 20%.
Friday Night
A 20 percent chance of showers and thunderstorms before 11pm. Partly cloudy, with a low around 72. Light and variable wind becoming east around 6 mph in the evening.
Saturday
Increasing clouds, with a high near 96. Heat index values as high as 101. South wind 5 to 7 mph becoming west in the afternoon.
Saturday Night
Partly cloudy, with a low around 73. Calm wind becoming south around 5 mph after midnight.
Sunday
A slight chance of showers between 1pm and 4pm, then a slight chance of showers and thunderstorms after 4pm. Mostly sunny, with a high near 93. Chance of precipitation is 20%.
Sunday Night
A 50 percent chance of showers and thunderstorms, mainly after 1am. Mostly cloudy, with a low around 68.
Monday
Showers likely, with thunderstorms also possible after 1pm. Mostly cloudy, with a high near 83. Chance of precipitation is 70%.
Monday Night
A 30 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 61.
Tuesday
Partly sunny, with a high near 73.
Tuesday Night
Mostly cloudy, with a low around 55.
Wednesday
Mostly sunny, with a high near 75.
Wednesday Night
Partly cloudy, with a low around 55.
Thursday
Mostly sunny, with a high near 77.
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Forecast Area
Tiles ©ESRI

ABOUT THIS FORECAST

 
Point Forecast:
Swansea IL
 38.55°N 89.98°W (Elev. 551 ft)
Last Update:
3:01 am CDT Sep 18, 2026
Forecast Valid:
3am CDT Sep 18, 2026-6pm CDT Sep 24, 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