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 Downtown Airport (KCPS)

Lat: 38.56°NLon: 90.15°WElev: 410ft.

Fair

95°F

35°C

Humidity 51%
Wind Speed E 5 mph
Barometer 30.08 in (1018.1 mb)
Dewpoint 74°F (23°C)
Visibility 10.00 mi
Heat Index106°F (41°C)
Last update 18 Sep 1:53 pm CDT
Extended Forecast for

Waterloo IL

Heat Advisory September 18, 02:28pm until September 19, 08:00pm
Click here for hazard details and duration
Heat Advisory
  •  
    Heat Advisory September 18, 02:28pm until September 19, 08:00pm

    NOW until 8:00pm Sat

    Heat Advisory

  • This Afternoon

    High: 97 °F

    Chance
    T-storms

  • Tonight

    Tonight: A 20 percent chance of showers and thunderstorms before 10pm. Mostly clear, with a low around 71. Light and variable wind.

    Low: 71 °F

    Slight Chance
    T-storms then
    Mostly Clear

  • Saturday

    Saturday: Increasing clouds and hot, with a high near 97. Heat index values as high as 101. Southwest wind 3 to 6 mph.

    High: 97 °F

    Hot

  • Saturday Night

    Saturday Night: Mostly cloudy, then gradually becoming mostly clear, with a low around 72. Calm wind becoming south around 5 mph in the evening.

    Low: 72 °F

    Decreasing
    Clouds

  • Sunday

    Sunday: Mostly sunny, with a high near 93. Southwest wind around 6 mph becoming northwest in the afternoon.

    High: 93 °F

    Mostly Sunny

  • Sunday Night

    Sunday Night: A 50 percent chance of showers and thunderstorms, mainly after 1am. Mostly cloudy, with a low around 67.

    Low: 67 °F

    Slight Chance
    T-storms then
    Chance
    Showers

  • Monday

    Monday: Showers likely, with thunderstorms also possible after 1pm. Mostly cloudy, with a high near 81. Chance of precipitation is 70%.

    High: 81 °F

    Showers
    Likely

  • Monday Night

    Monday Night: A slight chance of showers and thunderstorms. Mostly cloudy, with a low around 60. Chance of precipitation is 20%.

    Low: 60 °F

    Slight Chance
    T-storms

Detailed Forecast

This Afternoon
A 30 percent chance of showers and thunderstorms, mainly after 5pm. Sunny and hot, with a high near 97. Heat index values as high as 106. Calm wind.
Tonight
A 20 percent chance of showers and thunderstorms before 10pm. Mostly clear, with a low around 71. Light and variable wind.
Saturday
Increasing clouds and hot, with a high near 97. Heat index values as high as 101. Southwest wind 3 to 6 mph.
Saturday Night
Mostly cloudy, then gradually becoming mostly clear, with a low around 72. Calm wind becoming south around 5 mph in the evening.
Sunday
Mostly sunny, with a high near 93. Southwest wind around 6 mph becoming northwest in the afternoon.
Sunday Night
A 50 percent chance of showers and thunderstorms, mainly after 1am. Mostly cloudy, with a low around 67.
Monday
Showers likely, with thunderstorms also possible after 1pm. Mostly cloudy, with a high near 81. Chance of precipitation is 70%.
Monday Night
A slight chance of showers and thunderstorms. Mostly cloudy, with a low around 60. Chance of precipitation is 20%.
Tuesday
Mostly cloudy, with a high near 71.
Tuesday Night
Mostly cloudy, with a low around 54.
Wednesday
Mostly sunny, with a high near 74.
Wednesday Night
Partly cloudy, with a low around 54.
Thursday
Mostly sunny, with a high near 75.
Basemap Options
Click map to change the forecast location
Loading map...
Forecast Area
Tiles ©ESRI

ABOUT THIS FORECAST

 
Point Forecast:
Waterloo IL
 38.33°N 90.16°W (Elev. 600 ft)
Last Update:
2:01 pm CDT Sep 18, 2026
Forecast Valid:
2pm CDT Sep 18, 2026-6pm CDT Sep 24, 2026
 
Forecast Discussion
 
Get as KML Get as XML

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