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

Marion - Williamson County Regional Airport (KMWA)

Lat: 37.77°NLon: 89.01°WElev: 486ft.

Partly Cloudy

84°F

29°C

Humidity 45%
Wind Speed S 6 mph
Barometer 29.95 in
Dewpoint 61°F (16°C)
Visibility 10.00 mi
Heat Index84°F (29°C)
Last update 20 Jun 3:45 pm CDT
Extended Forecast for

Simpson IL

  • This Afternoon

    This Afternoon: Sunny, with a high near 87. Calm wind.

    High: 87 °F

    Sunny

  • Tonight

    Tonight: Mostly clear, with a low around 65. Calm wind.

    Low: 65 °F

    Mostly Clear

  • Sunday

    Sunday: Showers and thunderstorms likely, mainly before 4pm, then showers likely and possibly a thunderstorm after 5pm. Increasing clouds, with a high near 88. Light south southeast wind becoming south southwest 8 to 13 mph in the morning. Winds could gust as high as 25 mph. Chance of precipitation is 60%.

    High: 88 °F

    Showers
    Likely

  • Sunday Night

    Sunday Night: Showers and thunderstorms before 2am, then showers and possibly a thunderstorm, mainly after 2am. Low around 71. South southwest wind 8 to 11 mph, with gusts as high as 23 mph. Chance of precipitation is 90%.

    Low: 71 °F

    T-storms

  • Monday

    Monday: Showers likely and possibly a thunderstorm before 1pm, then a chance of showers and thunderstorms after 1pm. Mostly cloudy, with a high near 82. Southwest wind around 8 mph becoming northwest in the afternoon. Chance of precipitation is 70%.

    High: 82 °F

    Showers
    Likely

  • Monday Night

    Monday Night: A slight chance of showers and thunderstorms before 7pm, then a slight chance of showers between 7pm and 1am. Partly cloudy, with a low around 62. North northwest wind around 6 mph becoming calm in the evening. Chance of precipitation is 20%.

    Low: 62 °F

    Slight Chance
    T-storms then
    Slight Chance
    Showers

  • Tuesday

    Tuesday: Mostly sunny, with a high near 83. Light northeast wind.

    High: 83 °F

    Mostly Sunny

  • Tuesday Night

    Tuesday Night: A slight chance of showers. Mostly clear, with a low around 63. Calm wind.

    Low: 63 °F

    Slight Chance
    Showers

  • Wednesday

    Wednesday: A slight chance of showers and thunderstorms after 1pm. Mostly sunny, with a high near 85. Light and variable wind.

    High: 85 °F

    Sunny then
    Slight Chance
    T-storms

Detailed Forecast

This Afternoon
Sunny, with a high near 87. Calm wind.
Tonight
Mostly clear, with a low around 65. Calm wind.
Sunday
Showers and thunderstorms likely, mainly before 4pm, then showers likely and possibly a thunderstorm after 5pm. Increasing clouds, with a high near 88. Light south southeast wind becoming south southwest 8 to 13 mph in the morning. Winds could gust as high as 25 mph. Chance of precipitation is 60%.
Sunday Night
Showers and thunderstorms before 2am, then showers and possibly a thunderstorm, mainly after 2am. Low around 71. South southwest wind 8 to 11 mph, with gusts as high as 23 mph. Chance of precipitation is 90%.
Monday
Showers likely and possibly a thunderstorm before 1pm, then a chance of showers and thunderstorms after 1pm. Mostly cloudy, with a high near 82. Southwest wind around 8 mph becoming northwest in the afternoon. Chance of precipitation is 70%.
Monday Night
A slight chance of showers and thunderstorms before 7pm, then a slight chance of showers between 7pm and 1am. Partly cloudy, with a low around 62. North northwest wind around 6 mph becoming calm in the evening. Chance of precipitation is 20%.
Tuesday
Mostly sunny, with a high near 83. Light northeast wind.
Tuesday Night
A slight chance of showers. Mostly clear, with a low around 63. Calm wind.
Wednesday
A slight chance of showers and thunderstorms after 1pm. Mostly sunny, with a high near 85. Light and variable wind.
Wednesday Night
Partly cloudy, with a low around 64. Calm wind.
Thursday
Mostly sunny, with a high near 84. Calm wind becoming west southwest around 5 mph in the afternoon.
Thursday Night
A slight chance of showers and thunderstorms. Mostly clear, with a low around 63. Calm wind.
Friday
A chance of showers and thunderstorms. Mostly sunny, with a high near 85. Light and variable wind.
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ABOUT THIS FORECAST

 
Point Forecast:
Simpson IL
 37.46°N 88.77°W
Last Update:
2:11 pm CDT Jun 20, 2026
Forecast Valid:
4pm CDT Jun 20, 2026-6pm CDT Jun 26, 2026
 
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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