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

Decatur Airport (KDEC)

Lat: 39.83°NLon: 88.87°WElev: 670ft.

Overcast

54°F

12°C

Humidity 83%
Wind Speed NA
Barometer 30.17 in (1021.2 mb)
Dewpoint 49°F (9°C)
Visibility 10.00 mi
Last update 20 May 4:54 am CDT
Extended Forecast for

Illiopolis IL

  • Overnight

    Overnight: A 20 percent chance of showers. Cloudy, with a low around 53. North wind around 10 mph, with gusts as high as 20 mph.

    Low: 53 °F

    Slight Chance
    Showers

  • Wednesday

    Wednesday: Cloudy, then gradually becoming mostly sunny, with a high near 68. North northeast wind 9 to 11 mph, with gusts as high as 20 mph.

    High: 68 °F

    Decreasing
    Clouds

  • Wednesday Night

    Wednesday Night: Mostly clear, with a low around 47. Northeast wind 9 to 11 mph, with gusts as high as 24 mph.

    Low: 47 °F

    Mostly Clear

  • Thursday

    Thursday: Mostly sunny, with a high near 70. East wind 10 to 14 mph, with gusts as high as 22 mph.

    High: 70 °F

    Mostly Sunny

  • Thursday Night

    Thursday Night: A 30 percent chance of showers after 1am. Mostly cloudy, with a low around 53. East northeast wind 11 to 13 mph, with gusts as high as 20 mph.

    Low: 53 °F

    Mostly Cloudy
    then Chance
    Showers

  • Friday

    Friday: Showers, with thunderstorms also possible after 1pm. High near 68. East wind 11 to 14 mph, with gusts as high as 21 mph. Chance of precipitation is 80%. New rainfall amounts between a quarter and half of an inch possible.

    High: 68 °F

    Showers

  • Friday Night

    Friday Night: A 30 percent chance of showers before 1am. Mostly cloudy, with a low around 57. East northeast wind 6 to 10 mph becoming west after midnight. Winds could gust as high as 16 mph.

    Low: 57 °F

    Chance
    Showers

  • Saturday

    Saturday: Mostly cloudy, with a high near 77.

    High: 77 °F

    Mostly Cloudy

  • Saturday Night

    Saturday Night: Mostly cloudy, with a low around 59.

    Low: 59 °F

    Mostly Cloudy

Detailed Forecast

Overnight
A 20 percent chance of showers. Cloudy, with a low around 53. North wind around 10 mph, with gusts as high as 20 mph.
Wednesday
Cloudy, then gradually becoming mostly sunny, with a high near 68. North northeast wind 9 to 11 mph, with gusts as high as 20 mph.
Wednesday Night
Mostly clear, with a low around 47. Northeast wind 9 to 11 mph, with gusts as high as 24 mph.
Thursday
Mostly sunny, with a high near 70. East wind 10 to 14 mph, with gusts as high as 22 mph.
Thursday Night
A 30 percent chance of showers after 1am. Mostly cloudy, with a low around 53. East northeast wind 11 to 13 mph, with gusts as high as 20 mph.
Friday
Showers, with thunderstorms also possible after 1pm. High near 68. East wind 11 to 14 mph, with gusts as high as 21 mph. Chance of precipitation is 80%. New rainfall amounts between a quarter and half of an inch possible.
Friday Night
A 30 percent chance of showers before 1am. Mostly cloudy, with a low around 57. East northeast wind 6 to 10 mph becoming west after midnight. Winds could gust as high as 16 mph.
Saturday
Mostly cloudy, with a high near 77.
Saturday Night
Mostly cloudy, with a low around 59.
Sunday
A 40 percent chance of showers before 1pm. Mostly cloudy, with a high near 79.
Sunday Night
A chance of showers. Mostly cloudy, with a low around 60.
Memorial Day
A chance of showers. Mostly cloudy, with a high near 81.
Monday Night
Mostly cloudy, with a low around 62.
Tuesday
A chance of showers and thunderstorms. Partly sunny, with a high near 84.
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Forecast Area
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ABOUT THIS FORECAST

 
Point Forecast:
Illiopolis IL
 39.85°N 89.26°W (Elev. 607 ft)
Last Update:
4:44 am CDT May 20, 2026
Forecast Valid:
5am CDT May 20, 2026-6pm CDT May 26, 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