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

Hazardous Weather Conditions

Current conditions at

Marion - Williamson County Regional Airport (KMWA)

Lat: 37.77°NLon: 89.01°WElev: 486ft.

Fair

77°F

25°C

Humidity 83%
Wind Speed S 8 mph
Barometer 30.08 in
Dewpoint 72°F (22°C)
Visibility 10.00 mi
Heat Index78°F (26°C)
Last update 9 Sep 3:35 am CDT
Extended Forecast for

Johnston City IL

Heat Advisory September 9, 11:00am until September 9, 08:00pm
Click here for hazard details and duration
Heat Advisory

  • Overnight

    Overnight: Clear, with a low around 75. South southwest wind around 9 mph.

    Low: 75 °F

    Clear

  • Wednesday

    Wednesday: A 40 percent chance of showers and thunderstorms, mainly after 5pm. Sunny and hot, with a high near 100. Heat index values as high as 109. West southwest wind 8 to 13 mph, with gusts as high as 18 mph.

    High: 100 °F

    Slight Chance
    Showers then
    Chance
    T-storms

  • Wednesday Night

    Wednesday Night: A chance of showers and thunderstorms, then showers likely and possibly a thunderstorm after 1am. Mostly cloudy, with a low around 72. Southwest wind around 5 mph becoming calm in the evening. Chance of precipitation is 70%.

    Low: 72 °F

    Chance
    T-storms then
    Showers
    Likely

  • Thursday

    Thursday: Showers and thunderstorms before 3pm, then showers likely and possibly a thunderstorm between 3pm and 4pm, then a chance of showers and thunderstorms after 4pm. High near 87. Calm wind becoming north northwest 5 to 8 mph in the morning. Chance of precipitation is 90%.

    High: 87 °F

    Showers then
    Showers
    Likely

  • Thursday Night

    Thursday Night: A 30 percent chance of showers and thunderstorms before 1am. Mostly cloudy, with a low around 66. Light north northeast wind.

    Low: 66 °F

    Chance
    Showers

  • Friday

    Friday: A chance of showers and thunderstorms between 1pm and 4pm, then a chance of showers after 4pm. Partly sunny, with a high near 87. Light and variable wind. Chance of precipitation is 30%.

    High: 87 °F

    Partly Sunny
    then Chance
    Showers

  • Friday Night

    Friday Night: Partly cloudy, with a low around 67. Calm wind.

    Low: 67 °F

    Partly Cloudy

  • Saturday

    Saturday: A slight chance of showers and thunderstorms after 1pm. Mostly sunny, with a high near 93. Calm wind becoming south southwest around 6 mph in the morning.

    High: 93 °F

    Mostly Sunny
    then Slight
    Chance
    T-storms

  • Saturday Night

    Saturday Night: A chance of showers and thunderstorms, mainly before 1am. Partly cloudy, with a low around 69. Calm wind.

    Low: 69 °F

    Chance
    Showers

Detailed Forecast

Overnight
Clear, with a low around 75. South southwest wind around 9 mph.
Wednesday
A 40 percent chance of showers and thunderstorms, mainly after 5pm. Sunny and hot, with a high near 100. Heat index values as high as 109. West southwest wind 8 to 13 mph, with gusts as high as 18 mph.
Wednesday Night
A chance of showers and thunderstorms, then showers likely and possibly a thunderstorm after 1am. Mostly cloudy, with a low around 72. Southwest wind around 5 mph becoming calm in the evening. Chance of precipitation is 70%.
Thursday
Showers and thunderstorms before 3pm, then showers likely and possibly a thunderstorm between 3pm and 4pm, then a chance of showers and thunderstorms after 4pm. High near 87. Calm wind becoming north northwest 5 to 8 mph in the morning. Chance of precipitation is 90%.
Thursday Night
A 30 percent chance of showers and thunderstorms before 1am. Mostly cloudy, with a low around 66. Light north northeast wind.
Friday
A chance of showers and thunderstorms between 1pm and 4pm, then a chance of showers after 4pm. Partly sunny, with a high near 87. Light and variable wind. Chance of precipitation is 30%.
Friday Night
Partly cloudy, with a low around 67. Calm wind.
Saturday
A slight chance of showers and thunderstorms after 1pm. Mostly sunny, with a high near 93. Calm wind becoming south southwest around 6 mph in the morning.
Saturday Night
A chance of showers and thunderstorms, mainly before 1am. Partly cloudy, with a low around 69. Calm wind.
Sunday
A slight chance of showers and thunderstorms after 1pm. Mostly sunny, with a high near 92. Calm wind becoming south southwest 5 to 8 mph in the afternoon.
Sunday Night
Mostly clear, with a low around 70. South wind 3 to 6 mph.
Monday
Sunny, with a high near 94. South southwest wind 6 to 13 mph.
Monday Night
Mostly clear, with a low around 71. South wind around 7 mph.
Tuesday
A chance of showers and thunderstorms. Sunny, with a high near 92. Southwest wind 7 to 10 mph.
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Forecast Area
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ABOUT THIS FORECAST

 
Point Forecast:
Johnston City IL
 37.82°N 88.91°W
Last Update:
3:21 am CDT Sep 9, 2026
Forecast Valid:
3am CDT Sep 9, 2026-6pm CDT Sep 15, 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