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

Hazardous Weather Conditions

Current conditions at

Decatur Airport (KDEC)

Lat: 39.83°NLon: 88.87°WElev: 670ft.

A Few Clouds

80°F

27°C

Humidity 85%
Wind Speed S 3 mph
Barometer 30.04 in (1016.6 mb)
Dewpoint 75°F (24°C)
Visibility 10.00 mi
Heat Index85°F (29°C)
Last update 15 Aug 7:54 pm CDT
Extended Forecast for

Illiopolis IL

  • Tonight

    Tonight: A 50 percent chance of showers and thunderstorms, mainly after 2am. Mostly cloudy, with a low around 75. South wind around 5 mph becoming light and variable.

    Low: 75 °F

    Slight Chance
    T-storms then
    Chance
    T-storms

  • Sunday

    Sunday: A 30 percent chance of showers and thunderstorms, mainly after 4pm. Partly sunny, with a high near 88. West northwest wind 6 to 9 mph.

    High: 88 °F

    Chance
    T-storms

  • Sunday Night

    Sunday Night: A 30 percent chance of showers and thunderstorms, mainly before 7pm. Partly cloudy, with a low around 68. North northwest wind 5 to 9 mph.

    Low: 68 °F

    Chance
    T-storms then
    Partly Cloudy

  • Monday

    Monday: Mostly sunny, with a high near 82. North northwest wind 6 to 9 mph.

    High: 82 °F

    Mostly Sunny

  • Monday Night

    Monday Night: Mostly clear, with a low around 63. North wind around 5 mph becoming calm in the evening.

    Low: 63 °F

    Mostly Clear

  • Tuesday

    Tuesday: Mostly sunny, with a high near 84. Calm wind becoming southwest around 5 mph in the afternoon.

    High: 84 °F

    Mostly Sunny

  • Tuesday Night

    Tuesday Night: A 50 percent chance of showers and thunderstorms after 1am. Partly cloudy, with a low around 68. South wind 3 to 7 mph.

    Low: 68 °F

    Partly Cloudy
    then Chance
    T-storms

  • Wednesday

    Wednesday: A chance of showers, with thunderstorms also possible after 1pm. Mostly cloudy, with a high near 82. Chance of precipitation is 50%.

    High: 82 °F

    Chance
    Showers then
    Chance
    T-storms

  • Wednesday Night

    Wednesday Night: Partly cloudy, with a low around 62.

    Low: 62 °F

    Partly Cloudy

Detailed Forecast

Tonight
A 50 percent chance of showers and thunderstorms, mainly after 2am. Mostly cloudy, with a low around 75. South wind around 5 mph becoming light and variable.
Sunday
A 30 percent chance of showers and thunderstorms, mainly after 4pm. Partly sunny, with a high near 88. West northwest wind 6 to 9 mph.
Sunday Night
A 30 percent chance of showers and thunderstorms, mainly before 7pm. Partly cloudy, with a low around 68. North northwest wind 5 to 9 mph.
Monday
Mostly sunny, with a high near 82. North northwest wind 6 to 9 mph.
Monday Night
Mostly clear, with a low around 63. North wind around 5 mph becoming calm in the evening.
Tuesday
Mostly sunny, with a high near 84. Calm wind becoming southwest around 5 mph in the afternoon.
Tuesday Night
A 50 percent chance of showers and thunderstorms after 1am. Partly cloudy, with a low around 68. South wind 3 to 7 mph.
Wednesday
A chance of showers, with thunderstorms also possible after 1pm. Mostly cloudy, with a high near 82. Chance of precipitation is 50%.
Wednesday Night
Partly cloudy, with a low around 62.
Thursday
Mostly sunny, with a high near 78.
Thursday Night
Partly cloudy, with a low around 60.
Friday
Mostly sunny, with a high near 79.
Friday Night
Partly cloudy, with a low around 61.
Saturday
Mostly sunny, with a high near 80.
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Forecast Area
Tiles ©ESRI

ABOUT THIS FORECAST

 
Point Forecast:
Illiopolis IL
 39.85°N 89.26°W (Elev. 607 ft)
Last Update:
8:06 pm CDT Aug 15, 2026
Forecast Valid:
8pm CDT Aug 15, 2026-6pm CDT Aug 22, 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